LINQ to SQL Group Join

In LINQ to SQL, a Join clause with an into expression is called a Group join. In LINQ to SQL, the Group join produces a sequence of object elements based on the matching elements from both collections.

Syntax of LINQ to SQL Group Join

Following is the syntax of using LINQ to SQL Group Join to get data from multiple tables.

 

var result = from ed in db.EmployeeDetails
             join d in db.Departments on ed.DeptId equals d.DeptId into edept
             from dpem in edept
             select new
             {
               Name = ed.EmpName,
               Department = dpem.DeptName
             };

If you observe the above syntax, we joined “EmployeeDetails”, “Departments” tables to get required data by using group join.

Example of LINQ to SQL Group Join

Before we start implementing the LINQ to SQL group join example first, we need to create a database with required tables and map those tables to LINQ to SQL file (.dbml). If you don't know the process, don't worry; check this link create and map database tables to LINQ to SQL file (.dbml).

 

Once we create and map required tables to the .dbml file now, we will show data in our application for that Right-click on the application à select Add à New Item à Select Web Form à Give name as Default.aspx and click OK button.

 

Now open the Default.aspx page and write the code as shown below.

 

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Show Employee Details in Gridview</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:GridView ID="gvDetails" runat="server"></asp:GridView>
</div>
</form>
</body>
</html>

Now open the code behind file and write the code as shown below.

 

protected void Page_Load(object sender, EventArgs e)
{
  EmployeeDBDataContext db = new EmployeeDBDataContext();
  if (!Page.IsPostBack)
  {
    var result = from ed in db.EmployeeDetails
                 join d in db.Departments on ed.DeptId equals d.DeptId into edept
                 from dpem in edept
                 select new
                 {
                   Name = ed.EmpName,
                   Location = ed.Location,
                   Gender = ed.Gender,
                   Department = dpem.DeptName
                 };
    gvDetails.DataSource = result;
    gvDetails.DataBind();
  }
}

If you observe the above example, we are trying to get data from the “EmployeeDetails” and “Departments” table using Group join.

Result of LINQ to SQL Group Join

Following is the result of the LINQ to SQL group join example.

 

LINQ to SQL Group Join Queries with Examples

 

This is how we can use LINQ to SQL Group join in c# to get the required data from multiple tables based on our requirements.

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