LINQ – Left Join

If you are familiar with SQL, there is nothing interesting in performing inner joins, here is an example (on AdventureWorks)

AdventureWorksDataContext dc = new AdventureWorksDataContext();
var employees =
    from employee in dc.Employees
    join contact in dc.Contacts on employee.ContactID equals contact.ContactID
    select new
    {
        Firstname = contact.FirstName
        , LastName = contact.LastName
        , Gender = employee.Gender
    };

foreach (var employee in employees)
    Console.WriteLine("Firstname: {0}, LastName: {1}, Gender: {2}", 
        employee.Firstname, employee.LastName, employee.Gender);

To perform a left outer join you need to fetch with DefaultIfEmpty() on the group join. That way you get the nulls(converted to default values).

var employees =
    from employee in dc.Employees
    join contact in dc.Contacts 
    on employee.ContactID equals contact.ContactID 
    into joinedEmployees
    from jEmployee in joinedEmployees.DefaultIfEmpty() 
    select new
    {
        Firstname = jEmployee.FirstName
        , LastName = jEmployee.LastName
        , Gender = employee.Gender
    };

foreach (var employee in employees)
    Console.WriteLine("Firstname: {0}, LastName: {1}, Gender: {2}", 
        employee.Firstname, employee.LastName, employee.Gender);