Thursday, May 10, 2012

LINQ to SQL – Join 2 Tables


LINQ to SQL – Join 2 Tables

Before writing a LINQ to SQL query, we first need to create a DataContext using the LINQ to SQL Classes template, to know more on how to create the DataContext refer to the post LINQ to SQL Sample

Once the DataContext is created we can query the Object model using LINQ queries, let us consider the Employee table which has the following structure.


In practical situations we will have to join more than one table to get the details for reporting. Assume we have the following data in the Employee and Department Tables

Table: Employee
ID
NAME
DOB
DOJ
Phone
Email
DepartmentID
Salery
1
Tom
11/11/1967
05/01/2009
123-123-1234
tom@abcsoftware.com
1
5000
2
Harry
10/07/1973
05/01/2009
123-123-1234
harry@abcsoftware.com
2
6000
3
Peter
12/07/1975
05/01/2009
111-222-3333
peter@abcsoftware.com
3
6500
4
John
05/04/1981
05/01/2009
111-222-3333
john@abcsoftware.com
3
7500
5
Charles
12/12/1973
05/01/2009
666-444-2222
charles@abcsoftware.com
4
6500

Table: Department
ID
NAME
1
Finance
2
Human Resources
3
IT
4
Sales
5
Marketing

The SQL Query to join the 2 tables is as follows

SELECT     E.ID, E.Name, E.Phone, D.Name AS Department
FROM         Employee AS E INNER JOIN
                      Department AS D ON E.DepartmentID = D.ID

This query will fetch the following data
ID
NAME
Phone
Department
1
Tom
123-123-1234
Finance
2
Harry
123-123-1234
Human Resources
3
Peter
111-222-3333
IT
4
John
111-222-3333
IT
5
Charles
666-444-2222
Sales

Now let us see how the same can be achieved using a LINQ query.

EmployeeClassesDataContext dbContext = new EmployeeClassesDataContext();

  var emp = (from e in dbContext.Employees
            from d in dbContext.Departments
            where e.DepartmentID == d.ID
            select new { e.ID, e.Name, e.Phone, Department = (d.Name)});

Alternatively we can also use the join keyword to form the query as follows.

    var emp = (from e in dbContext.Employees 
                         join d in dbContext.Departments
                         on e.DepartmentID equals d.ID
            select new { e.ID, e.Name, e.Phone, Department = (d.Name)});

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