LINQ to SQL – LEFT OUTER JOIN

LINQ to SQL – LEFT OUTER JOIN

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.

A LEFT OUTER JOIN is used to fetch all the details from the table which is in the Left side in the Query and the matching details from the table in the right side in the query.

Assume we have the following data in the Employee and Department Tables

Table: Employee

ID	NAME	Phone	Email	DepartmentID	Salery
1	Tom	123-123-1234	tom@abcsoftware.com	1	5000
2	Harry	123-123-1234	harry@abcsoftware.com	2	6000
3	Peter	111-222-3333	peter@abcsoftware.com	3	6500
4	John	111-222-3333	john@abcsoftware.com	3	7500
5	Charles	666-444-2222	charles@abcsoftware.com	NULL	6500

Table: Department

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

The LEFT  OUTER JOIN 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	NULL

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

        join d in dbContext.Departments on e.DepartmentID equals d.ID into dj

        from d in dj.DefaultIfEmpty()

        select new { e.ID, e.Name, e.Phone, Department = (d.Name)});

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