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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