LINQ - Quick Guide
LINQ - Overview
Developers across the world have always encountered problems in querying data because of the lack of a defined path and need to master a multiple of technologies like SQL, Web Services, XQuery, etc.
Introduced in Visual Studio 2008 and designed by Anders Hejlsberg, LINQ (Language Integrated Query) allows writing queries even without the knowledge of query languages like SQL, XML etc. LINQ queries can be written for diverse data types.
Example of a LINQ query
C#
using System;
using System.Linq;
class Program {
static void Main() {
string[] words = {"hello", "wonderful", "LINQ", "beautiful", "world"};
//Get only short words
var shortWords = from word in words where word.Length <= 5 select word;
//Print each word out
foreach (var word in shortWords) {
Console.WriteLine(word);
}
Console.ReadLine();
}
}
VB
Module Module1
Sub Main()
Dim words As String() = {"hello", "wonderful", "LINQ", "beautiful", "world"}
' Get only short words
Dim shortWords = From word In words _ Where word.Length <= 5 _ Select word
' Print each word out.
For Each word In shortWords
Console.WriteLine(word)
Next
Console.ReadLine()
End Sub
End Module
When the above code of C# or VB is compiled and executed, it produces the following result −
hello
LINQ
world
Syntax of LINQ
There are two syntaxes of LINQ. These are the following ones.
Lamda (Method) Syntax
var longWords = words.Where( w ⇒ w.length > 10);
Dim longWords = words.Where(Function(w) w.length > 10)
Query (Comprehension) Syntax
var longwords = from w in words where w.length > 10;
Dim longwords = from w in words where w.length > 10
Types of LINQ
The types of LINQ are mentioned below in brief.
- LINQ to Objects
- LINQ to XML(XLINQ)
- LINQ to DataSet
- LINQ to SQL (DLINQ)
- LINQ to Entities
Apart from the above, there is also a LINQ type named PLINQ which is Microsoft’s parallel LINQ.
LINQ Architecture in .NET
LINQ has a 3-layered architecture in which the uppermost layer consists of the language extensions and the bottom layer consists of data sources that are typically objects implementing IEnumerable <T> or IQueryable <T> generic interfaces. The architecture is shown below.
Query Expressions
Query expression is nothing but a LINQ query, expressed in a form similar to that of SQL with query operators like Select, Where and OrderBy. Query expressions usually start with the keyword "From".
To access standard LINQ query operators, the namespace System.Query should be imported by default. These expressions are written within a declarative query syntax which was C# 3.0.
Below is an example to show a complete query operation which consists of data source creation, query expression definition and query execution.
C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Operators {
class LINQQueryExpressions {
static void Main() {
// Specify the data source.
int[] scores = new int[] { 97, 92, 81, 60 };
// Define the query expression.
IEnumerable<int> scoreQuery = from score in scores where score > 80 select score;
// Execute the query.
foreach (int i in scoreQuery) {
Console.Write(i + " ");
}
Console.ReadLine();
}
}
}
When the above code is compiled and executed, it produces the following result −
97 92 81
Extension Methods
Introduced with .NET 3.5, Extension methods are declared in static classes only and allow inclusion of custom methods to objects to perform some precise query operations to extend a class without being an actual member of that class. These can be overloaded also.
In a nutshell, extension methods are used to translate query expressions into traditional method calls (object-oriented).
Difference between LINQ and Stored Procedure
There is an array of differences existing between LINQ and Stored procedures. These differences are mentioned below.
Stored procedures are much faster than a LINQ query as they follow an expected execution plan.
It is easy to avoid run-time errors while executing a LINQ query than in comparison to a stored procedure as the former has Visual Studio’s Intellisense support as well as full-type checking during compile-time.
LINQ allows debugging by making use of .NET debugger which is not in case of stored procedures.
LINQ offers support for multiple databases in contrast to stored procedures, where it is essential to re-write the code for diverse types of databases.
Deployment of LINQ based solution is easy and simple in comparison to deployment of a set of stored procedures.
Need For LINQ
Prior to LINQ, it was essential to learn C#, SQL, and various APIs that bind together the both to form a complete application. Since, these data sources and programming languages face an impedance mismatch; a need of short coding is felt.
Below is an example of how many diverse techniques were used by the developers while querying a data before the advent of LINQ.
SqlConnection sqlConnection = new SqlConnection(connectString);
SqlConnection.Open();
System.Data.SqlClient.SqlCommand sqlCommand = new SqlCommand();
sqlCommand.Connection = sqlConnection;
sqlCommand.CommandText = "Select * from Customer";
return sqlCommand.ExecuteReader (CommandBehavior.CloseConnection)
Interestingly, out of the featured code lines, query gets defined only by the last two. Using LINQ, the same data query can be written in a readable color-coded form like the following one mentioned below that too in a very less time.
Northwind db = new Northwind(@"C:\Data\Northwnd.mdf");
var query = from c in db.Customers select c;
Advantages of LINQ
LINQ offers a host of advantages and among them the foremost is its powerful expressiveness which enables developers to express declaratively. Some of the other advantages of LINQ are given below.
LINQ offers syntax highlighting that proves helpful to find out mistakes during design time.
LINQ offers IntelliSense which means writing more accurate queries easily.
Writing codes is quite faster in LINQ and thus development time also gets reduced significantly.
LINQ makes easy debugging due to its integration in the C# language.
Viewing relationship between two tables is easy with LINQ due to its hierarchical feature and this enables composing queries joining multiple tables in less time.
LINQ allows usage of a single LINQ syntax while querying many diverse data sources and this is mainly because of its unitive foundation.
LINQ is extensible that means it is possible to use knowledge of LINQ to querying new data source types.
LINQ offers the facility of joining several data sources in a single query as well as breaking complex problems into a set of short queries easy to debug.
LINQ offers easy transformation for conversion of one data type to another like transforming SQL data to XML data.
LINQ - Environment Setup
Before starting with LINQ programs, it is best to first understand the nuances of setting up a LINQ environment. LINQ needs a .NET framework, a revolutionary platform to have a diverse kind of applications. A LINQ query can be written either in C# or Visual Basic conveniently.
Microsoft offers tools for both of these languages i.e. C# and Visual Basic by means of Visual Studio. Our examples are all compiled and written in Visual Studio 2010. However, Visual Basic 2013 edition is also available for use. It is the latest version and has many similarities with Visual Studio 2012.
Getting Visual Studio 2010 Installed on Windows 7
Visual Studio can be installed either from an installation media like a DVD. Administrator credentials are required to install Visual Basic 2010 on your system successfully. It is vital to disconnect all removable USB from the system prior to installation otherwise the installation may get failed. Some of the hardware requirements essential to have for installation are the following ones.
Hardware Requirements
- 1.6 GHz or more
- 1 GB RAM
- 3 GB(Available hard-disk space)
- 5400 RPM hard-disk drive
- DirectX 9 compatible video card
- DVD-ROM drive
Installation Steps
Step 1 − First after inserting the DVD with Visual Studio 2010 Package, click on Install or run program from your media appearing in a pop-up box on the screen.
Step 2 − Now set up for Visual Studio will appear on the screen. Choose Install Microsoft Visual Studio 2010.
Step 3 − As soon as you will click, it the process will get initiated and a set up window will appear on your screen. After completion of loading of the installation components which will take some time, click on Next button to move to the next step.
Step 4 − This is the last step of installation and a start page will appear in which simply choose "I have read and accept the license terms" and click on Next button.
Step 5 − Now select features to install from the options page appearing on your screen. You can either choose Full or Custom option. If you have less disk space than required shown in the disk space requirements, then go for Custom.
Step 6 − When you choose Custom option, the following window will appear. Select the features that you want to install and click Update or else go to step 7. However, it is recommended not to go with the custom option as in future, you may need the features you have chosen to not have.
Step 7 − Soon a pop up window will be shown and the installation will start which may take a long time. Remember, this is for installing all the components.
Step 8 − Finally, you will be able to view a message in a window that the installation has been completed successfully. Click Finish.
Writing C# Program using LINQ in Visual Studio 2010
Start Visual Studio 2010 Ultimate edition and choose File followed by New Project from the menu.
A new project dialog box will appear on your screen.
Now choose Visual C# as a category under installed templates and next choose Console Application template as shown in figure below.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace HelloWorld {
class Program {
static void Main(string[] args) {
Console.WriteLine("Hello World")
Console.ReadKey();
}
}
}
Writing VB Program using LINQ in Visual Studio 2010
Start Visual Studio 2010 Ultimate edition and choose File followed by New Project from the menu.
A new project dialog box will appear on your screen.
Now chose Visual Basic as a category under installed templates and next choose Console Application template.
Give a name to your project in the bottom name box and press OK.
You will get a screen with Module1.vb. Start writing your VB code here using LINQ.
Module Module1
Sub Main()
Console.WriteLine("Hello World")
Console.ReadLine()
End Sub
End Module
When the above code of C# or VB is cimpiled and run, it produces the following result −
Hello World
LINQ - Query Operators
A set of extension methods forming a query pattern is known as LINQ Standard Query Operators. As building blocks of LINQ query expressions, these operators offer a range of query capabilities like filtering, sorting, projection, aggregation, etc.
LINQ standard query operators can be categorized into the following ones on the basis of their functionality.
- Filtering Operators
- Join Operators
- Projection Operations
- Sorting Operators
- Grouping Operators
- Conversions
- Concatenation
- Aggregation
- Quantifier Operations
- Partition Operations
- Generation Operations
- Set Operations
- Equality
- Element Operators
Filtering Operators
Filtering is an operation to restrict the result set such that it has only selected elements satisfying a particular condition.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| where |
Filter values based on a predicate function |
where |
Where |
| OfType |
Filter values based on their ability to be as a specified type |
Not Applicable |
Not Applicable |
Join Operators
Joining refers to an operation in which data sources with difficult to follow relationships with each other in a direct way are targeted.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| Join |
The operator join two sequences on basis of matching keys |
join … in … on … equals … |
From x In …, y In … Where x.a = y.a |
| GroupJoin |
Join two sequences and group the matching elements |
join … in … on … equals … into … |
Group Join … In … On … |
Projection Operations
Projection is an operation in which an object is transformed into an altogether new form with only specific properties.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| Select |
The operator projects values on basis of a transform function |
select |
Select |
| SelectMany |
The operator project the sequences of values which are based on a transform function as well as flattens them into a single sequence |
Use multiple from clauses |
Use multiple From clauses |
Sorting Operators
A sorting operation allows ordering the elements of a sequence on basis of a single or more attributes.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| OrderBy |
The operator sort values in an ascending order |
orderby |
Order By |
| OrderByDescending |
The operator sort values in a descending order |
orderby ... descending |
Order By ... Descending |
| ThenBy |
Executes a secondary sorting in an ascending order |
orderby …, … |
Order By …, … |
| ThenByDescending |
Executes a secondary sorting in a descending order |
orderby …, … descending |
Order By …, … Descending |
| Reverse |
Performs a reversal of the order of the elements in a collection |
Not Applicable |
Not Applicable |
Grouping Operators
The operators put data into some groups based on a common shared attribute.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| GroupBy |
Organize a sequence of items in groups and return them as an IEnumerable collection of type IGrouping<key, element> |
group … by -or- group … by … into … |
Group … By … Into … |
| ToLookup |
Execute a grouping operation in which a sequence of key pairs are returned |
Not Applicable |
Not Applicable |
Conversions
The operators change the type of input objects and are used in a diverse range of applications.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| AsEnumerable |
Returns the input typed as IEnumerable<T> |
Not Applicable |
Not Applicable |
| AsQueryable |
A (generic) IEnumerable is converted to a (generic) IQueryable |
Not Applicable |
Not Applicable |
| Cast |
Performs casting of elements of a collection to a specified type |
Use an explicitly typed range variable. Eg:from string str in words |
From … As … |
| OfType |
Filters values on basis of their , depending on their capability to be cast to a particular type |
Not Applicable |
Not Applicable |
| ToArray |
Forces query execution and does conversion of a collection to an array |
Not Applicable |
Not Applicable |
| ToDictionary |
On basis of a key selector function set elements into a Dictionary<TKey, TValue> and forces execution of a LINQ query |
Not Applicable |
Not Applicable |
| ToList |
Forces execution of a query by converting a collection to a List<T> |
Not Applicable |
Not Applicable |
| ToLookup |
Forces execution of a query and put elements into a Lookup<TKey, TElement> on basis of a key selector function |
Not Applicable |
Not Applicable |
Concatenation
Performs concatenation of two sequences and is quite similar to the Union operator in terms of its operation except of the fact that this does not remove duplicates.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| Concat |
Two sequences are concatenated for the formation of a single one sequence. |
Not Applicable |
Not Applicable |
Aggregation
Performs any type of desired aggregation and allows creating custom aggregations in LINQ.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| Aggregate |
Operates on the values of a collection to perform custom aggregation operation |
Not Applicable |
Not Applicable |
| Average |
Average value of a collection of values is calculated |
Not Applicable |
Aggregate … In … Into Average() |
| Count |
Counts the elements satisfying a predicate function within collection |
Not Applicable |
Aggregate … In … Into Count() |
| LonCount |
Counts the elements satisfying a predicate function within a huge collection |
Not Applicable |
Aggregate … In … Into LongCount() |
| Max |
Find out the maximum value within a collection |
Not Applicable |
Aggregate … In … Into Max() |
| Min |
Find out the minimum value existing within a collection |
Not Applicable |
Aggregate … In … Into Min() |
| Sum |
Find out the sum of a values within a collection |
Not Applicable |
Aggregate … In … Into Sum() |
Quantifier Operations
These operators return a Boolean value i.e. True or False when some or all elements within a sequence satisfy a specific condition.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| All |
Returns a value ‘True’ if all elements of a sequence satisfy a predicate condition |
Not Applicable |
Aggregate … In … Into All(…) |
| Any |
Determines by searching a sequence that whether any element of the same satisfy a specified condition |
Not Applicable |
Aggregate … In … Into Any() |
| Contains |
Returns a ‘True’ value if finds that a specific element is there in a sequence if the sequence doe not contains that specific element , ‘false’ value is returned |
Not Applicable |
Not Applicable |
Partition Operators
Divide an input sequence into two separate sections without rearranging the elements of the sequence and then returning one of them.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| Skip |
Skips some specified number of elements within a sequence and returns the remaining ones |
Not Applicable |
Skip |
| SkipWhile |
Same as that of Skip with the only exception that number of elements to skip are specified by a Boolean condition |
Not Applicable |
Skip While |
| Take |
Take a specified number of elements from a sequence and skip the remaining ones |
Not Applicable |
Take |
| TakeWhile |
Same as that of Take except the fact that number of elements to take are specified by a Boolean condition |
Not Applicable |
Take While |
Generation Operations
A new sequence of values is created by generational operators.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| DefaultIfEmpty |
When applied to an empty sequence, generate a default element within a sequence |
Not Applicable |
Not Applicable |
| Empty |
Returns an empty sequence of values and is the most simplest generational operator |
Not Applicable |
Not Applicable |
| Range |
Generates a collection having a sequence of integers or numbers |
Not Applicable |
Not Applicable |
| Repeat |
Generates a sequence containing repeated values of a specific length |
Not Applicable |
Not Applicable |
Set Operations
There are four operators for the set operations, each yielding a result based on different criteria.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| Distinct |
Results a list of unique values from a collection by filtering duplicate data if any |
Not Applicable |
Distinct |
| Except |
Compares the values of two collections and return the ones from one collection who are not in the other collection |
Not Applicable |
Not Applicable |
| Intersect |
Returns the set of values found t be identical in two separate collections |
Not Applicable |
Not Applicable |
| Union |
Combines content of two different collections into a single list that too without any duplicate content |
Not Applicable |
Not Applicable |
Equality
Compares two sentences (enumerable ) and determine are they an exact match or not.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| SequenceEqual |
Results a Boolean value if two sequences are found to be identical to each other |
Not Applicable |
Not Applicable |
Element Operators
Except the DefaultIfEmpty, all the rest eight standard query element operators return a single element from a collection.
Show Examples
| Operator |
Description |
C# Query Expression Syntax |
VB Query Expression Syntax |
| ElementAt |
Returns an element present within a specific index in a collection |
Not Applicable |
Not Applicable |
| ElementAtOrDefault |
Same as ElementAt except of the fact that it also returns a default value in case the specific index is out of range |
Not Applicable |
Not Applicable |
| First |
Retrieves the first element within a collection or the first element satisfying a specific condition |
Not Applicable |
Not Applicable |
| FirstOrDefault |
Same as First except the fact that it also returns a default value in case there is no existence of such elements |
Not Applicable |
Not Applicable |
| Last |
Retrieves the last element present in a collection or the last element satisfying a specific condition |
Not Applicable |
Not Applicable |
| LastOrDefault |
Same as Last except the fact that it also returns a default value in case there is no existence of any such element |
Not Applicable |
Not Applicable |
| Single |
Returns the lone element of a collection or the lone element that satisfy a certain condition |
Not Applicable |
Not Applicable |
| SingleOrDefault |
Same as Single except that it also returns a default value if there is no existence of any such lone element |
Not Applicable |
Not Applicable |
| DefaultIfEmpty |
Returns a default value if the collection or list is empty or null |
Not Applicable |
Not Applicable |
LINQ - SQL
LINQ to SQL offers an infrastructure (run-time) for the management of relational data as objects. It is a component of version 3.5 of the .NET Framework and ably does the translation of language-integrated queries of the object model into SQL. These queries are then sent to the database for the purpose of execution. After obtaining the results from the database, LINQ to SQL again translates them to objects.
Introduction of LINQ To SQL
For most ASP.NET developers, LINQ to SQL (also known as DLINQ) is an electrifying part of Language Integrated Query as this allows querying data in SQL server database by using usual LINQ expressions. It also allows to update, delete, and insert data, but the only drawback from which it suffers is its limitation to the SQL server database. However, there are many benefits of LINQ to SQL over ADO.NET like reduced complexity, few lines of coding and many more.
Below is a diagram showing the execution architecture of LINQ to SQL.
How to Use LINQ to SQL?
Step 1 − Make a new “Data Connection” with database server. View &arrar; Server Explorer &arrar; Data Connections &arrar; Add Connection
Step 2 − Add LINQ To SQL class file
Step 3 − Select tables from database and drag and drop into the new LINQ to SQL class file.
Step 4 − Added tables to class file.
Querying with LINQ to SQL
The rules for executing a query with LINQ to SQL is similar to that of a standard LINQ query i.e. query is executed either deferred or immediate. There are various components that play a role in execution of a query with LINQ to SQL and these are the following ones.
LINQ to SQL API − requests query execution on behalf of an application and sent it to LINQ to SQL Provider.
LINQ to SQL Provider − converts query to Transact SQL(T-SQL) and sends the new query to the ADO Provider for execution.
ADO Provider − After execution of the query, send the results in the form of a DataReader to LINQ to SQL Provider which in turn converts it into a form of user object.
It should be noted that before executing a LINQ to SQL query, it is vital to connect to the data source via DataContext class.
Insert, Update and Delete using LINQ To SQL
Add OR Insert
C#
using System;
using System.Linq;
namespace LINQtoSQL {
class LinqToSQLCRUD {
static void Main(string[] args) {
string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString();
LinqToSQLDataContext db = new LinqToSQLDataContext(connectString);
//Create new Employee
Employee newEmployee = new Employee();
newEmployee.Name = "Michael";
newEmployee.Email = "yourname@companyname.com";
newEmployee.ContactNo = "343434343";
newEmployee.DepartmentId = 3;
newEmployee.Address = "Michael - USA";
//Add new Employee to database
db.Employees.InsertOnSubmit(newEmployee);
//Save changes to Database.
db.SubmitChanges();
//Get new Inserted Employee
Employee insertedEmployee = db.Employees.FirstOrDefault(e ⇒e.Name.Equals("Michael"));
Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3}, Address = {4}",
insertedEmployee.EmployeeId, insertedEmployee.Name, insertedEmployee.Email,
insertedEmployee.ContactNo, insertedEmployee.Address);
Console.WriteLine("\nPress any key to continue.");
Console.ReadKey();
}
}
}
VB
Module Module1
Sub Main()
Dim connectString As String = System.Configuration.ConfigurationManager.ConnectionStrings("LinqToSQLDBConnectionString").ToString()
Dim db As New LinqToSQLDataContext(connectString)
Dim newEmployee As New Employee()
newEmployee.Name = "Michael"
newEmployee.Email = "yourname@companyname.com"
newEmployee.ContactNo = "343434343"
newEmployee.DepartmentId = 3
newEmployee.Address = "Michael - USA"
db.Employees.InsertOnSubmit(newEmployee)
db.SubmitChanges()
Dim insertedEmployee As Employee = db.Employees.FirstOrDefault(Function(e) e.Name.Equals("Michael"))
Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3},
Address = {4}", insertedEmployee.EmployeeId, insertedEmployee.Name,
insertedEmployee.Email, insertedEmployee.ContactNo, insertedEmployee.Address)
Console.WriteLine(vbLf & "Press any key to continue.")
Console.ReadKey()
End Sub
End Module
When the above code of C# or VB is compiled and run, it produces the following result −
Emplyee ID = 4, Name = Michael, Email = yourname@companyname.com, ContactNo =
343434343, Address = Michael - USA
Press any key to continue.
Update
C#
using System;
using System.Linq;
namespace LINQtoSQL {
class LinqToSQLCRUD {
static void Main(string[] args) {
string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString();
LinqToSQLDataContext db = new LinqToSQLDataContext(connectString);
//Get Employee for update
Employee employee = db.Employees.FirstOrDefault(e =>e.Name.Equals("Michael"));
employee.Name = "George Michael";
employee.Email = "yourname@companyname.com";
employee.ContactNo = "99999999";
employee.DepartmentId = 2;
employee.Address = "Michael George - UK";
//Save changes to Database.
db.SubmitChanges();
//Get Updated Employee
Employee updatedEmployee = db.Employees.FirstOrDefault(e ⇒e.Name.Equals("George Michael"));
Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3}, Address = {4}",
updatedEmployee.EmployeeId, updatedEmployee.Name, updatedEmployee.Email,
updatedEmployee.ContactNo, updatedEmployee.Address);
Console.WriteLine("\nPress any key to continue.");
Console.ReadKey();
}
}
}
VB
Module Module1
Sub Main()
Dim connectString As String = System.Configuration.ConfigurationManager.ConnectionStrings("LinqToSQLDBConnectionString").ToString()
Dim db As New LinqToSQLDataContext(connectString)
Dim employee As Employee = db.Employees.FirstOrDefault(Function(e) e.Name.Equals("Michael"))
employee.Name = "George Michael"
employee.Email = "yourname@companyname.com"
employee.ContactNo = "99999999"
employee.DepartmentId = 2
employee.Address = "Michael George - UK"
db.SubmitChanges()
Dim updatedEmployee As Employee = db.Employees.FirstOrDefault(Function(e) e.Name.Equals("George Michael"))
Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3},
Address = {4}", updatedEmployee.EmployeeId, updatedEmployee.Name,
updatedEmployee.Email, updatedEmployee.ContactNo, updatedEmployee.Address)
Console.WriteLine(vbLf & "Press any key to continue.")
Console.ReadKey()
End Sub
End Module
When the above code of C# or Vb is compiled and run, it produces the following result −
Emplyee ID = 4, Name = George Michael, Email = yourname@companyname.com, ContactNo =
999999999, Address = Michael George - UK
Press any key to continue.
Delete
C#
using System;
using System.Linq;
namespace LINQtoSQL {
class LinqToSQLCRUD {
static void Main(string[] args) {
string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString();
LinqToSQLDataContext db = newLinqToSQLDataContext(connectString);
//Get Employee to Delete
Employee deleteEmployee = db.Employees.FirstOrDefault(e ⇒e.Name.Equals("George Michael"));
//Delete Employee
db.Employees.DeleteOnSubmit(deleteEmployee);
//Save changes to Database.
db.SubmitChanges();
//Get All Employee from Database
var employeeList = db.Employees;
foreach (Employee employee in employeeList) {
Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3}",
employee.EmployeeId, employee.Name, employee.Email, employee.ContactNo);
}
Console.WriteLine("\nPress any key to continue.");
Console.ReadKey();
}
}
}
VB
Module Module1
Sub Main()
Dim connectString As String = System.Configuration.ConfigurationManager.ConnectionStrings("LinqToSQLDBConnectionString").ToString()
Dim db As New LinqToSQLDataContext(connectString)
Dim deleteEmployee As Employee = db.Employees.FirstOrDefault(Function(e) e.Name.Equals("George Michael"))
db.Employees.DeleteOnSubmit(deleteEmployee)
db.SubmitChanges()
Dim employeeList = db.Employees
For Each employee As Employee In employeeList
Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3}",
employee.EmployeeId, employee.Name, employee.Email, employee.ContactNo)
Next
Console.WriteLine(vbLf & "Press any key to continue.")
Console.ReadKey()
End Sub
End Module
When the above code of C# or VB is compiled and run, it produces the following result −
Emplyee ID = 1, Name = William, Email = abc@gy.co, ContactNo = 999999999
Emplyee ID = 2, Name = Miley, Email = amp@esds.sds, ContactNo = 999999999
Emplyee ID = 3, Name = Benjamin, Email = asdsad@asdsa.dsd, ContactNo =
Press any key to continue.
LINQ - Objects
LINQ to Objects offers usage of any LINQ query supporting IEnumerable<T>for accessing in-memory data collections without any need of LINQ provider (API) as in case of LINQ to SQL or LINQ to XML.
Introduction of LINQ to Objects
Queries in LINQ to Objects return variables of type usually IEnumerable<T> only. In short, LINQ to Objects offers a fresh approach to collections as earlier, it was vital to write long coding (foreach loops of much complexity) for retrieval of data from a collection which is now replaced by writing declarative code which clearly describes the desired data that is required to retrieve.
There are also many advantages of LINQ to Objects over traditional foreach loops like more readability, powerful filtering, capability of grouping, enhanced ordering with minimal application coding. Such LINQ queries are also more compact in nature and are portable to any other data sources without any modification or with just a little modification.
Below is a simple LINQ to Objects example −
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace LINQtoObjects {
class Program {
static void Main(string[] args) {
string[] tools = { "Tablesaw", "Bandsaw", "Planer", "Jointer", "Drill", "Sander" };
var list = from t in tools select t;
StringBuilder sb = new StringBuilder();
foreach (string s in list) {
sb.Append(s + Environment.NewLine);
}
Console.WriteLine(sb.ToString(), "Tools");
Console.ReadLine();
}
}
}
In the example, an array of strings (tools) is used as the collection of objects to be queried using LINQ to Objects.
Objects query is:
var list = from t in tools select t;
When the above code is compiled and executed, it produces the following result −
Tablesaw
Bandsaw
Planer
Jointer
Drill
Sander
Querying in Memory Collections Using LINQ to Objects
C#
using System;
using System.Collections.Generic;
using System.Linq;
namespace LINQtoObjects {
class Department {
public int DepartmentId { get; set; }
public string Name { get; set; }
}
class LinqToObjects {
static void Main(string[] args) {
List<Department> departments = new List<Department>();
departments.Add(new Department { DepartmentId = 1, Name = "Account" });
departments.Add(new Department { DepartmentId = 2, Name = "Sales" });
departments.Add(new Department { DepartmentId = 3, Name = "Marketing" });
var departmentList = from d in departments
select d;
foreach (var dept in departmentList) {
Console.WriteLine("Department Id = {0} , Department Name = {1}",
dept.DepartmentId, dept.Name);
}
Console.WriteLine("\nPress any key to continue.");
Console.ReadKey();
}
}
}
VB
Imports System.Collections.Generic
Imports System.Linq
Module Module1
Sub Main(ByVal args As String())
Dim account As New Department With {.Name = "Account", .DepartmentId = 1}
Dim sales As New Department With {.Name = "Sales", .DepartmentId = 2}
Dim marketing As New Department With {.Name = "Marketing", .DepartmentId = 3}
Dim departments As New System.Collections.Generic.List(Of Department)(New Department() {account, sales, marketing})
Dim departmentList = From d In departments
For Each dept In departmentList
Console.WriteLine("Department Id = {0} , Department Name = {1}", dept.DepartmentId, dept.Name)
Next
Console.WriteLine(vbLf & "Press any key to continue.")
Console.ReadKey()
End Sub
Class Department
Public Property Name As String
Public Property DepartmentId As Integer
End Class
End Module
When the above code of C# or VB is compiled and executed, it produces the following result −
Department Id = 1, Department Name = Account
Department Id = 2, Department Name = Sales
Department Id = 3, Department Name = Marketing
Press any key to continue.
LINQ - Dataset
A Dataset offers an extremely useful data representation in memory and is used for a diverse range of data based applications. LINQ to Dataset as one of the technology of LINQ to ADO.NET facilitates performing queries on the data of a Dataset in a hassle-free manner and enhance productivity.
Introduction of LINQ To Dataset
LINQ to Dataset has made the task of querying simple for the developers. They don’t need to write queries in a specific query language instead the same can be written in programming language. LINQ to Dataset is also usable for querying where data is consolidated from multiple data sources. This also does not need any LINQ provider just like LINQ to SQL and LINQ to XML for accessing data from in memory collections.
Below is a simple example of a LINQ to Dataset query in which a data source is first obtained and then the dataset is filled with two data tables. A relationship is established between both the tables and a LINQ query is created against both tables by the means of join clause. Finally, foreach loop is used to display the desired results.
C#
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LINQtoDataset {
class Program {
static void Main(string[] args) {
string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString();
string sqlSelect = "SELECT * FROM Department;" + "SELECT * FROM Employee;";
// Create the data adapter to retrieve data from the database
SqlDataAdapter da = new SqlDataAdapter(sqlSelect, connectString);
// Create table mappings
da.TableMappings.Add("Table", "Department");
da.TableMappings.Add("Table1", "Employee");
// Create and fill the DataSet
DataSet ds = new DataSet();
da.Fill(ds);
DataRelation dr = ds.Relations.Add("FK_Employee_Department",
ds.Tables["Department"].Columns["DepartmentId"],
ds.Tables["Employee"].Columns["DepartmentId"]);
DataTable department = ds.Tables["Department"];
DataTable employee = ds.Tables["Employee"];
var query = from d in department.AsEnumerable()
join e in employee.AsEnumerable()
on d.Field<int>("DepartmentId") equals
e.Field<int>("DepartmentId")
select new {
EmployeeId = e.Field<int>("EmployeeId"),
Name = e.Field<string>("Name"),
DepartmentId = d.Field<int>("DepartmentId"),
DepartmentName = d.Field<string>("Name")
};
foreach (var q in query) {
Console.WriteLine("Employee Id = {0} , Name = {1} , Department Name = {2}",
q.EmployeeId, q.Name, q.DepartmentName);
}
Console.WriteLine("\nPress any key to continue.");
Console.ReadKey();
}
}
}
VB
Imports System.Data.SqlClient
Imports System.Linq
Module LinqToDataSet
Sub Main()
Dim connectString As String = System.Configuration.ConfigurationManager.ConnectionStrings("LinqToSQLDBConnectionString").ToString()
Dim sqlSelect As String = "SELECT * FROM Department;" + "SELECT * FROM Employee;"
Dim sqlCnn As SqlConnection = New SqlConnection(connectString)
sqlCnn.Open()
Dim da As New SqlDataAdapter
da.SelectCommand = New SqlCommand(sqlSelect, sqlCnn)
da.TableMappings.Add("Table", "Department")
da.TableMappings.Add("Table1", "Employee")
Dim ds As New DataSet()
da.Fill(ds)
Dim dr As DataRelation = ds.Relations.Add("FK_Employee_Department", ds.Tables("Department").Columns("DepartmentId"), ds.Tables("Employee").Columns("DepartmentId"))
Dim department As DataTable = ds.Tables("Department")
Dim employee As DataTable = ds.Tables("Employee")
Dim query = From d In department.AsEnumerable()
Join e In employee.AsEnumerable() On d.Field(Of Integer)("DepartmentId") Equals
e.Field(Of Integer)("DepartmentId")
Select New Person With { _
.EmployeeId = e.Field(Of Integer)("EmployeeId"),
.EmployeeName = e.Field(Of String)("Name"),
.DepartmentId = d.Field(Of Integer)("DepartmentId"),
.DepartmentName = d.Field(Of String)("Name")
}
For Each e In query
Console.WriteLine("Employee Id = {0} , Name = {1} , Department Name = {2}", e.EmployeeId, e.EmployeeName, e.DepartmentName)
Next
Console.WriteLine(vbLf & "Press any key to continue.")
Console.ReadKey()
End Sub
Class Person
Public Property EmployeeId As Integer
Public Property EmployeeName As String
Public Property DepartmentId As Integer
Public Property DepartmentName As String
End Class
End Module
When the above code of C# or VB is compiled and executed, it produces the following result −
Employee Id = 1, Name = William, Department Name = Account
Employee Id = 2, Name = Benjamin, Department Name = Account
Employee Id = 3, Name = Miley, Department Name = Sales
Press any key to continue.
Querying Dataset using LinQ to Dataset
Before beginning querying a Dataset using LINQ to Dataset, it is vital to load data to a Dataset and this is done by either using DataAdapter class or by LINQ to SQL. Formulation of queries using LINQ to Dataset is quite similar to formulating queries by using LINQ alongside other LINQ enabled data sources.
Single-Table Query
In the following single-table query, all online orders are collected from the SalesOrderHeaderTtable and then order ID, Order date as well as order number are displayed as output.
C#
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqToDataset {
class SingleTable {
static void Main(string[] args) {
string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString();
string sqlSelect = "SELECT * FROM Department;";
// Create the data adapter to retrieve data from the database
SqlDataAdapter da = new SqlDataAdapter(sqlSelect, connectString);
// Create table mappings
da.TableMappings.Add("Table", "Department");
// Create and fill the DataSet
DataSet ds = new DataSet();
da.Fill(ds);
DataTable department = ds.Tables["Department"];
var query = from d in department.AsEnumerable()
select new {
DepartmentId = d.Field<int>("DepartmentId"),
DepartmentName = d.Field<string>("Name")
};
foreach (var q in query) {
Console.WriteLine("Department Id = {0} , Name = {1}",
q.DepartmentId, q.DepartmentName);
}
Console.WriteLine("\nPress any key to continue.");
Console.ReadKey();
}
}
}
VB
Imports System.Data.SqlClient
Imports System.Linq
Module LinqToDataSet
Sub Main()
Dim connectString As String = System.Configuration.ConfigurationManager.ConnectionStrings("LinqToSQLDBConnectionString").ToString()
Dim sqlSelect As String = "SELECT * FROM Department;"
Dim sqlCnn As SqlConnection = New SqlConnection(connectString)
sqlCnn.Open()
Dim da As New SqlDataAdapter
da.SelectCommand = New SqlCommand(sqlSelect, sqlCnn)
da.TableMappings.Add("Table", "Department")
Dim ds As New DataSet()
da.Fill(ds)
Dim department As DataTable = ds.Tables("Department")
Dim query = From d In department.AsEnumerable()
Select New DepartmentDetail With {
.DepartmentId = d.Field(Of Integer)("DepartmentId"),
.DepartmentName = d.Field(Of String)("Name")
}
For Each e In query
Console.WriteLine("Department Id = {0} , Name = {1}", e.DepartmentId, e.DepartmentName)
Next
Console.WriteLine(vbLf & "Press any key to continue.")
Console.ReadKey()
End Sub
Public Class DepartmentDetail
Public Property DepartmentId As Integer
Public Property DepartmentName As String
End Class
End Module
When the above code of C# or VB is compiled and executed, it produces the following result −
Department Id = 1, Name = Account
Department Id = 2, Name = Sales
Department Id = 3, Name = Pre-Sales
Department Id = 4, Name = Marketing
Press any key to continue.
LINQ - XML
LINQ to XML offers easy accessibility to all LINQ functionalities like standard query operators, programming interface, etc. Integrated in the .NET framework, LINQ to XML also makes the best use of .NET framework functionalities like debugging, compile-time checking, strong typing and many more to say.
Introduction of LINQ to XML
While using LINQ to XML, loading XML documents into memory is easy and more easier is querying and document modification. It is also possible to save XML documents existing in memory to disk and to serialize them. It eliminates the need for a developer to learn the XML query language which is somewhat complex.
LINQ to XML has its power in the System.Xml.Linq namespace. This has all the 19 necessary classes to work with XML. These classes are the following ones.
- XAttribute
- XCData
- XComment
- XContainer
- XDeclaration
- XDocument
- XDocumentType
- XElement
- XName
- XNamespace
- XNode
- XNodeDocumentOrderComparer
- XNodeEqualityComparer
- XObject
- XObjectChange
- XObjectChangeEventArgs
- XObjectEventHandler
- XProcessingInstruction
- XText
Read an XML File using LINQ
C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;
namespace LINQtoXML {
class ExampleOfXML {
static void Main(string[] args) {
string myXML = @"<Departments>
<Department>Account</Department>
<Department>Sales</Department>
<Department>Pre-Sales</Department>
<Department>Marketing</Department>
</Departments>";
XDocument xdoc = new XDocument();
xdoc = XDocument.Parse(myXML);
var result = xdoc.Element("Departments").Descendants();
foreach (XElement item in result) {
Console.WriteLine("Department Name - " + item.Value);
}
Console.WriteLine("\nPress any key to continue.");
Console.ReadKey();
}
}
}
VB
Imports System.Collections.Generic
Imports System.Linq
Imports System.Xml.Linq
Module Module1
Sub Main(ByVal args As String())
Dim myXML As String = "<Departments>" & vbCr & vbLf &
"<Department>Account</Department>" & vbCr & vbLf &
"<Department>Sales</Department>" & vbCr & vbLf &
"<Department>Pre-Sales</Department>" & vbCr & vbLf &
"<Department>Marketing</Department>" & vbCr & vbLf &
"</Departments>"
Dim xdoc As New XDocument()
xdoc = XDocument.Parse(myXML)
Dim result = xdoc.Element("Departments").Descendants()
For Each item As XElement In result
Console.WriteLine("Department Name - " + item.Value)
Next
Console.WriteLine(vbLf & "Press any key to continue.")
Console.ReadKey()
End Sub
End Module
When the above code of C# or VB is compiled and executed, it produces the following result −
Department Name - Account
Department Name - Sales
Department Name - Pre-Sales
Department Name - Marketing
Press any key to continue.
Add New Node
C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;
namespace LINQtoXML {
class ExampleOfXML {
static void Main(string[] args) {
string myXML = @"<Departments>
<Department>Account</Department>
<Department>Sales</Department>
<Department>Pre-Sales</Department>
<Department>Marketing</Department>
</Departments>";
XDocument xdoc = new XDocument();
xdoc = XDocument.Parse(myXML);
//Add new Element
xdoc.Element("Departments").Add(new XElement("Department", "Finance"));
//Add new Element at First
xdoc.Element("Departments").AddFirst(new XElement("Department", "Support"));
var result = xdoc.Element("Departments").Descendants();
foreach (XElement item in result) {
Console.WriteLine("Department Name - " + item.Value);
}
Console.WriteLine("\nPress any key to continue.");
Console.ReadKey();
}
}
}
VB
Imports System.Collections.Generic
Imports System.Linq
Imports System.Xml.Linq
Module Module1
Sub Main(ByVal args As String())
Dim myXML As String = "<Departments>" & vbCr & vbLf &
"<Department>Account</Department>" & vbCr & vbLf &
"<Department>Sales</Department>" & vbCr & vbLf &
"<Department>Pre-Sales</Department>" & vbCr & vbLf &
"<Department>Marketing</Department>" & vbCr & vbLf &
"</Departments>"
Dim xdoc As New XDocument()
xdoc = XDocument.Parse(myXML)
xdoc.Element("Departments").Add(New XElement("Department", "Finance"))
xdoc.Element("Departments").AddFirst(New XElement("Department", "Support"))
Dim result = xdoc.Element("Departments").Descendants()
For Each item As XElement In result
Console.WriteLine("Department Name - " + item.Value)
Next
Console.WriteLine(vbLf & "Press any key to continue.")
Console.ReadKey()
End Sub
End Module
When the above code of C# or VB is compiled and executed, it produces the following result −
Department Name - Support
Department Name - Account
Department Name - Sales
Department Name - Pre-Sales
Department Name - Marketing
Department Name - Finance
Press any key to continue.
Deleting Particular Node
C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;
namespace LINQtoXML {
class ExampleOfXML {
static void Main(string[] args) {
string myXML = @"<Departments>
<Department>Support</Department>
<Department>Account</Department>
<Department>Sales</Department>
<Department>Pre-Sales</Department>
<Department>Marketing</Department>
<Department>Finance</Department>
</Departments>";
XDocument xdoc = new XDocument();
xdoc = XDocument.Parse(myXML);
//Remove Sales Department
xdoc.Descendants().Where(s =>s.Value == "Sales").Remove();
var result = xdoc.Element("Departments").Descendants();
foreach (XElement item in result) {
Console.WriteLine("Department Name - " + item.Value);
}
Console.WriteLine("\nPress any key to continue.");
Console.ReadKey();
}
}
}
VB
Imports System.Collections.Generic
Imports System.Linq
Imports System.Xml.Linq
Module Module1
Sub Main(args As String())
Dim myXML As String = "<Departments>" & vbCr & vbLf &
"<Department>Support</Department>" & vbCr & vbLf &
"<Department>Account</Department>" & vbCr & vbLf &
"<Department>Sales</Department>" & vbCr & vbLf &
"<Department>Pre-Sales</Department>" & vbCr & vbLf &
"<Department>Marketing</Department>" & vbCr & vbLf &
"<Department>Finance</Department>" & vbCr & vbLf &
"</Departments>"
Dim xdoc As New XDocument()
xdoc = XDocument.Parse(myXML)
xdoc.Descendants().Where(Function(s) s.Value = "Sales").Remove()
Dim result = xdoc.Element("Departments").Descendants()
For Each item As XElement In result
Console.WriteLine("Department Name - " + item.Value)
Next
Console.WriteLine(vbLf & "Press any key to continue.")
Console.ReadKey()
End Sub
End Module
When the above code of C# or VB is compiled and executed, it produces the following result −
Department Name - Support
Department Name - Account
Department Name - Pre-Sales
Department Name - Marketing
Department Name - Finance
Press any key to continue.
LINQ - Entities
A part of the ADO.NET Entity Framework, LINQ to Entities is more flexible than LINQ to SQL, but is not much popular because of its complexity and lack of key features. However, it does not have the limitations of LINQ to SQL that allows data query only in SQL server database as LINQ to Entities facilitates data query in a large number of data providers like Oracle, MySQL, etc.
Moreover, it has got a major support from ASP.Net in the sense that users can make use of a data source control for executing a query via LINQ to Entities and facilitates binding of the results without any need of extra coding.
LINQ to Entities has for these advantages become the standard mechanism for the usage of LINQ on databases nowadays. It is also possible with LINQ to Entities to change queried data details and committing a batch update easily. What is the most intriguing fact about LINQ to Entities is that it has same syntax like that of SQL and even has the same group of standard query operators like Join, Select, OrderBy, etc.
LINQ to Entities Query Creation and Execution Process
Construction of an ObjectQuery instance out of an ObjectContext (Entity Connection)
Composing a query either in C# or Visual Basic (VB) by using the newly constructed instance
Conversion of standard query operators of LINQ as well as LINQ expressions into command trees
Executing the query passing any exceptions encountered to the client directly
Returning to the client all the query results
ObjectContext is here the primary class that enables interaction with Entity Data Model or in other words acts as a bridge that connects LINQ to the database. Command trees are here query representation with compatibility with the Entity framework.
The Entity Framework, on the other hand, is actually Object Relational Mapper abbreviated generally as ORM by the developers that does the generation of business objects as well as entities as per the database tables and facilitates various basic operations like create, update, delete and read. The following illustration shows the entity framework and its components.
Example of ADD, UPDATE, and DELETE using LINQ with Entity Model
First add Entity Model by following below steps.
Step 1 − Right click on project and click add new item will open window as per below. Select ADO.NET Entity Data Model and specify name and click on Add.
Step 2 − Select Generate from database.
Step 3 − Choose Database Connection from the drop-down menu.
Step 4 − Select all the tables.
Now write the following code.
using DataAccess;
using System;
using System.Linq;
namespace LINQTOSQLConsoleApp {
public class LinqToEntityModel {
static void Main(string[] args) {
using (LinqToSQLDBEntities context = new LinqToSQLDBEntities()) {
//Get the List of Departments from Database
var departmentList = from d in context.Departments
select d;
foreach (var dept in departmentList) {
Console.WriteLine("Department Id = {0} , Department Name = {1}",
dept.DepartmentId, dept.Name);
}
//Add new Department
DataAccess.Department department = new DataAccess.Department();
department.Name = "Support";
context.Departments.Add(department);
context.SaveChanges();
Console.WriteLine("Department Name = Support is inserted in Database");
//Update existing Department
DataAccess.Department updateDepartment = context.Departments.FirstOrDefault(d ⇒d.DepartmentId == 1);
updateDepartment.Name = "Account updated";
context.SaveChanges();
Console.WriteLine("Department Name = Account is updated in Database");
//Delete existing Department
DataAccess.Department deleteDepartment = context.Departments.FirstOrDefault(d ⇒d.DepartmentId == 3);
context.Departments.Remove(deleteDepartment);
context.SaveChanges();
Console.WriteLine("Department Name = Pre-Sales is deleted in Database");
//Get the Updated List of Departments from Database
departmentList = from d in context.Departments
select d;
foreach (var dept in departmentList) {
Console.WriteLine("Department Id = {0} , Department Name = {1}",
dept.DepartmentId, dept.Name);
}
}
Console.WriteLine("\nPress any key to continue.");
Console.ReadKey();
}
}
}
When the above code is compiled and executed, it produces the following result −
LINQ - Lambda Expressions
The term ‘Lambda expression’ has derived its name from ‘lambda’ calculus which in turn is a mathematical notation applied for defining functions. Lambda expressions as a LINQ equation’s executable part translate logic in a way at run time so it can pass on to the data source conveniently. However, lambda expressions are not just limited to find application in LINQ only.
These expressions are expressed by the following syntax −
(Input parameters) ⇒ Expression or statement block
Here is an example of a lambda expression −
y ⇒ y * y
The above expression specifies a parameter named y and that value of y is squared. However, it is not possible to execute a lambda expression in this form. Example of a lambda expression in C# is shown below.
C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace lambdaexample {
class Program {
delegate int del(int i);
static void Main(string[] args) {
del myDelegate = y ⇒ y * y;
int j = myDelegate(5);
Console.WriteLine(j);
Console.ReadLine();
}
}
}
VB
Module Module1
Private Delegate Function del(ByVal i As Integer) As Integer
Sub Main(ByVal args As String())
Dim myDelegate As del = Function(y) y * y
Dim j As Integer = myDelegate(5)
Console.WriteLine(j)
Console.ReadLine()
End Sub
End Module
When the above code of C# or VB is compiled and executed, it produces the following result −
25
Expression Lambda
As the expression in the syntax of lambda expression shown above is on the right hand side, these are also known as expression lambda.
Async Lambdas
The lambda expression created by incorporating asynchronous processing by the use of async keyword is known as async lambdas. Below is an example of async lambda.
Func<Task<string>> getWordAsync = async()⇒ “hello”;
Lambda in Standard Query Operators
A lambda expression within a query operator is evaluated by the same upon demand and continually works on each of the elements in the input sequence and not the whole sequence. Developers are allowed by Lambda expression to feed their own logic into the standard query operators. In the below example, the developer has used the ‘Where’ operator to reclaim the odd values from given list by making use of a lambda expression.
C#
//Get the average of the odd Fibonacci numbers in the series...
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace lambdaexample {
class Program {
static void Main(string[] args) {
int[] fibNum = { 1, 1, 2, 3, 5, 8, 13, 21, 34 };
double averageValue = fibNum.Where(num ⇒ num % 2 == 1).Average();
Console.WriteLine(averageValue);
Console.ReadLine();
}
}
}
VB
Module Module1
Sub Main()
Dim fibNum As Integer() = {1, 1, 2, 3, 5, 8, 13, 21, 34}
Dim averageValue As Double = fibNum.Where(Function(num) num Mod 2 = 1).Average()
Console.WriteLine(averageValue)
Console.ReadLine()
End Sub
End Module
When the above code is compiled and executed, it produces the following result −
7.33333333333333
Type Inference in Lambda
In C#, type inference is used conveniently in a variety of situations and that too without specifying the types explicitly. However in case of a lambda expression, type inference will work only when each type has been specified as the compiler must be satisfied. Let’s consider the following example.
delegate int Transformer (int i);
Here the compiler employ the type inference to draw upon the fact that x is an integer and this is done by examining the parameter type of the Transformer.
Variable Scope in Lambda Expression
There are some rules while using variable scope in a lambda expression like variables that are initiated within a lambda expression are not meant to be visible in an outer method. There is also a rule that a captured variable is not to be garbage collected unless the delegate referencing the same becomes eligible for the act of garbage collection. Moreover, there is a rule that prohibits a return statement within a lambda expression to cause return of an enclosing method.
Here is an example to demonstrate variable scope in lambda expression.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace lambdaexample {
class Program {
delegate bool D();
delegate bool D2(int i);
class Test {
D del;
D2 del2;
public void TestMethod(int input) {
int j = 0;
// Initialize the delegates with lambda expressions.
// Note access to 2 outer variables.
// del will be invoked within this method.
del = () ⇒ { j = 10; return j > input; };
// del2 will be invoked after TestMethod goes out of scope.
del2 = (x) ⇒ { return x == j; };
// Demonstrate value of j:
// The delegate has not been invoked yet.
Console.WriteLine("j = {0}", j); // Invoke the delegate.
bool boolResult = del();
Console.WriteLine("j = {0}. b = {1}", j, boolResult);
}
static void Main() {
Test test = new Test();
test.TestMethod(5);
// Prove that del2 still has a copy of
// local variable j from TestMethod.
bool result = test.del2(10);
Console.WriteLine(result);
Console.ReadKey();
}
}
}
}
When the above code is compiled and executed, it produces the following result −
j = 0
j = 10. b = True
True
Expression Tree
Lambda expressions are used in Expression Tree construction extensively. An expression tree give away code in a data structure resembling a tree in which every node is itself an expression like a method call or can be a binary operation like x<y. Below is an example of usage of lambda expression for constructing an expression tree.
Statement Lambda
There is also statement lambdas consisting of two or three statements, but are not used in construction of expression trees. A return statement must be written in a statement lambda.
Syntax of statement lambda
(params)⇒ {statements}
Example of a statement lambda
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
namespace lambdaexample {
class Program {
static void Main(string[] args) {
int[] source = new[] { 3, 8, 4, 6, 1, 7, 9, 2, 4, 8 };
foreach (int i in source.Where(x ⇒
{
if (x <= 3)
return true;
else if (x >= 7)
return true;
return false;
}
))
Console.WriteLine(i);
Console.ReadLine();
}
}
}
When the above code is compiled and executed, it produces the following result −
3
8
1
7
9
2
8
Lambdas are employed as arguments in LINQ queries based on methods and never allowed to have a place on the left side of operators like is or as just like anonymous methods. Although, Lambda expressions are much alike anonymous methods, these are not at all restricted to be used as delegates only.
Points to remember while using lambda expressions
A lambda expression can return a value and may have parameters.
Parameters can be defined in a myriad of ways with a lambda expression.
If there is single statement in a lambda expression, there is no need of curly brackets whereas if there are multiple statements, curly brackets as well as return value are essential to write.
With lambda expressions, it is possible to access variables present outside of the lambda expression block by a feature known as closure. Use of closure should be done cautiously to avoid any problem.
It is impossible to execute any unsafe code inside any lambda expression.
Lambda expressions are not meant to be used on the operator’s left side.
LINQ - ASP.Net
As a set of .NET framework extensions, LINQ is the preferred mechanism for data access by ASP.NET developers. ASP.NET 3.5 has a built-in tool LINQDataSource control that enables usage of LINQ easily in ASP.NET. ASP.NET uses the above-mentioned control as a data source. Real life projects mostly encompass websites or windows applications and so to understand better the concept of LINQ with ASP.NET, let’s start with creating a ASP.NET website that make use of the LINQ features.
For this, it is essential to get installed Visual Studio and .NET framework on your system. Once you have opened Visual Studio, go to File → New → Website. A pop up window will open as shown in below figure.
Now, under the templates in the left hand side, there will be two language options to create the website. Choose Visual C# and select ASP.NET Empty Web Site.
Select the folder where you want to save new website on your system. Then press OK and soon Solution Explorer appears on your screen containing all the web files. Right click on Default.aspx in the Solution Explorer and choose View in Browser to view the default ASP.NET website in the browser. Soon your new ASP.NET website will open in the web browser, as shown in the following screenshot.
.aspx is in fact the major file extension used in ASP.NET websites. Visual Studio by default creates all the necessary pages for a basic website like Home page and About Us page where you can place your content conveniently. The code for the website is generated automatically here and can be viewed too.
LINQDataSource Control
It is possible to UPDATE, INSERT and DELETE data in the pages of ASP.NET website with the help of LINQDataSource control. There is absolutely no need for specification of SQL commands as LINQDataSource control employs dynamically created commands for such operations.
The control enables a user to make use of LINQ in an ASP.NET web page conveniently by property setting in the markup text. LINQDataSource is very similar to that of controls like SqlDataSource as well as ObjectDataSource as it can be used in binding other ASP.NET controls present on a page to a data source. So, we must have a database to explain the various functions invoked by the LINQDataSource Control.
Before going to start explanation of the control usage in ASP.NET web page form, it is essential to open the Microsoft Visual Studio Toolbox and drag and drop LINQDataSource control to .aspx page of ASP.NET website like below figure.
The next step is to configure LINQDataSource by selecting all the columns for the employee record.
Now add a GridView Control to the .aspx page and configure it like shown in below figure. The GridView control is powerful and offers flexibility to work with the data. Soon after configuring the control, it will appear in the browser.
The coding that can be viewed now on your screen for the .aspx page will be −
<!DOCTYPE html>
<html>
<head runat = "server">
<title></title>
</head>
<body>
<form id = "form1" runat = "server">
<div>
<asp:GridView ID = "GridView1" runat = "server" AutoGenerateColumns = "False"
DataKeyNames = "ContactID" DataSourceID = "LINQDataSource1">
<Columns>
<asp:BoundField DataField = "ContactID" HeaderText = "ContactID"
InsertVisible = "False" ReadOnly="True" SortExpression = "ContactID" />
<asp:CheckBoxField DataField = "NameStyle" HeaderText = "NameStyle"
SortExpression = "NameStyle" />
<asp:BoundField DataField = "Title" HeaderText = "Title" SortExpression = "Title" />
<asp:BoundField DataField = "FirstName" HeaderText = "FirstName"
SortExpression="FirstName" />
<asp:BoundField DataField = "MiddleName" HeaderText = "MiddleName"
SortExpression = "MiddleName" />
<asp:BoundField DataField = "LastName" HeaderText = "LastName"
SortExpression = "LastName" />
<asp:BoundField DataField = "Suffix" HeaderText = "Suffix"
SortExpression = "Suffix" />
<asp:BoundField DataField = "EmailAddress" HeaderText = "EmailAddress"
SortExpression = "EmailAddress" />
</Columns>
</asp:GridView>
<br />
</div>
<asp:LINQDataSource ID = "LINQDataSource1" runat = "server"
ContextTypeName = "LINQWebApp1.AdventureWorksDataContext" EntityTypeName = ""
TableName = "Contacts">
</asp:LINQDataSource>
</form>
</body>
</html>
Here it should be noted that it is vital to set the property ContextTypeName to that of the class representing the database. For example, here it is given as LINQWebApp1.AdventureWorksDataContext as this action will make the needed connection between LINQDataSource and the database.
INSERT, UPDATE, and DELETE data in ASP.NET Page using LINQ
After completing all the above steps rigorously, choose the LINQDataSource Tasks from the LINQDataSource Control and choose all the three boxes for enable insert, enable update and enable delete from the same, as shown in the following screenshot.
Soon the declarative markup will get displayed on your screen as the following one.
<asp:LINQDataSource
ContextTypeName = "LINQWebApp1.AdventureWorksDataContext"
TableName = "Contacts"
EnableUpdate = "true"
EnableInsert = "true"
EnableDelete = "true"
ID = "LINQDataSource1"
runat = "server">
</asp:LINQDataSource>
Now since there are multiple rows and columns, it is better to add another control on your .aspx form named as Detail View or Master control below the Grid View control to display only the details of a selected row of the grid. Choose the Detail View Tasks from the Detail View control and select the check boxes as shown below.
Now, just save the changes and press Ctrl + F5 to view the page in your browser where it is now possible to delete, update, insert any record on the detail view control.
