IEnumerable vs IQueryable in LINQ

     How to write code via IEnumerable and IQueryable and what the differences are between them. IEnumerable and IQueryable are used for data manipulation in LINQ from the database and collections. For getting the data from the database, I have created a table named "Employee" that has some data and looks like:

Then creating the Data Context class (.dbml class) in your project that converts the database table named "Employee" as a class.
Now I will tell you the functionality and some basic differences between IEnumerable and IQueryable using the object of the Data Context class..

IEnumerable Code



SQL statement after execution of above query

After the execution of line number 18, the SQL statement will look like the following until the end:

IQueryable Code



SQL statement after execution of the preceding query

After the execution of line number 22, the SQL statement will look like:

But after the execution of line number 23, SQL statement will add the Top for the filtering.

In both syntaxes I am accessing the data from the Employee table and then taking only 3 rows from that data. 

Differences

IEnumerable

1. IEnumerable exists in the System.Collections namespace.
    
2. IEnumerable is suitable for querying data from in-memory collections like List, Array and so on.
    
3. While querying data from the database, IEnumerable executes "select query" on the server-side, loads data in-memory on the client-side and then filters the data. 
    
   
4. IEnumerable is beneficial for LINQ to Object and LINQ to XML queries.

IQueryable

1. IQueryable exists in the System.Linq Namespace.
   
   
    
2. IQueryable is suitable for querying data from out-memory (like remote database, service) collections. 
3. While querying data from a database, IQueryable executes a "select query" on server-side with all filters.
   
   
   
4. IQueryable is beneficial for LINQ to SQL queries.

Simple SELECT, INSERT, UPDATE and DELETE Using LINQ to SQL

Language-INtegrated Query (LINQ) is a Microsoft .NET Framework component that adds native data querying capabilities to .NET languages. In other words LINQ has the power of querying on any source of data (Collection of objects, database tables or XML Files). We can easily retrieve data from any object that implements the IEnumerable<T> interface and any provider that implements the IQueryable<T> interface.

Microsoft basically divides LINQ into the following three areas:

• LINQ to Object : Queries performed against in-memory data
• LINQ to ADO.Net
• LINQ to SQL (formerly DLinq) : Queries performed against the relation database; only Microsoft SQL Server is supported.
• LINQ to DataSet : Supports queries by using ADO.NET data sets and data tables.
• LINQ to Entities : Microsoft ORM solution
• LINQ to XML (formerly XLinq) : Queries performed against the XML source.

LINQ to SQL

LINQ to SQL translates our actions to SQL and submits the changes to the database. Here we will perform Select, Insert, Update and Delete operations on a COURSE table.

Step 1: Create a COURSE Table in the database

CREATE TABLE COURSE

{

    course_id int identity(1,1) primary key,

    course_name navarchar(50) not null,

    course_desc nvarchar(255,

    modified_date date

}

Step 2: Create a ContextData file using the Object Relational Designer:

Create a new item, select the LINQ to SQL classes (as shown in the following figure) and name it Operation.dbml.

After clicking the Add button the ContextData file is created. Now we should drag all the tables onto the left-hand side of the designer and save (as shown in the following figure). This will create all the mappings and settings for each table and their entities.

For .dbml files the database connection string is defined in the web.config file as:

<connectionStrings>

    <add name="nageshConnectionString" connectionString="Data Source=.\sqlexpress;Initial Catalog=nagesh;Persist Security Info=True;User ID=sa;Password=nagesh"

      providerName="System.Data.SqlClient" />

  </connectionStrings>

We can use a connection string from the web.config file or we can pass a connection string as a parameter in the constructor of the DataContext class to create an object of the DataContext class.

The SELECT Operation

private void GetCourses()
{
      //create DataContext object
      OperationDataContext OdContext = new OperationDataContext();
      var courseTable = from course in OdContext.GetTable<COURSE>() select course;
      //grdCourse is gridview id
      grdCourse.DataSource = courseTable;
      grdCourse.DataBind();
}

The INSERT Operation

private void AddNewCourse()
{
      //Data maping object to our database
      OperationDataContext OdContext = new OperationDataContext();
      COURSE objCourse = new COURSE();
      objCourse.course_name = "B.Tech";
      objCourse.course_desc = "Bachelor Of Technology";
      objCourse.modified_date = DateTime.Now;
      //Adds an entity in a pending insert state to this System.Data.Linq.Table<TEntity>and parameter is the entity which to be added
      OdContext.COURSEs.InsertOnSubmit(objCourse);
      // executes the appropriate commands to implement the changes to the database
      OdContext.SubmitChanges();
}

The Update Operation

private void UpdateCourse()
{
      OperationDataContext OdContext = new OperationDataContext();
      //Get Single course which need to update
      COURSE objCourse = OdContext.COURSEs.Single(course => course.course_name == "B.Tech");
      //Field which will be update
      objCourse.course_desc = "Bachelor of Technology";
      // executes the appropriate commands to implement the changes to the database
      OdContext.SubmitChanges();
 }

The DELETE Operation

private void DeleteCourse()
{
      OperationDataContext OdContext = new OperationDataContext();
      //Get Single course which need to Delete
      COURSE objCourse = OdContext.COURSEs.Single(course => course.course_name == "B.Tech");
      //Puts an entity from this table into a pending delete state and parameter is the entity which to be deleted.
      OdContext.COURSEs.DeleteOnSubmit(objCourse);
      // executes the appropriate commands to implement the changes to the database
      OdContext.SubmitChanges();
}

Conculsion

To perform select, insert, update and delete operations we create a table and create a data context class; in other words a dbml file. In this file designer view we drag and drop the COURSE table from the Server Explorer. This data context class is an Object and table mapping and we perform the operation on the object and database updated according to the action using the submitChanges() method.