使用 JOIN 到 LINQ 语句的 SQL 语句

Question

How would you write the following SQL as a Linq-statement?

SELECT * 
FROM Projekt i 
LEFT JOIN Projekt j on i.name=j.id

Answer 1

If you have for example these two classes:

public class Employee
{
    public int ID { get; set; }
    public string Name { get; set; }
    public int AddressId { get; set; }
}

public class Address
{
    public int ID { get; set; }
    public string AddressLine { get; set; }
}

then with Method Syntax (MS) for LEFT OUTER JOIN we'll have this code below:

var JoinedTables = context.Employee.GroupJoin(Address,
                                              emp => emp.AddressId,
                                              add => add.ID,
                                              (emp, add) => new { emp, add })
                                   .SelectMany(x => x.add.DefaultIfEmpty(),
                                              (employee, address) => new { employee, address }))
                                   .ToList();

But with Query Syntax (QS)

which is more understandable for humans

for LEFT OUTER JOIN again all you have to do is:

var JoinedTables = (from emp in Employee
                   join add in Address
                   on emp.AddressId equals add.ID
                   into EmployeeAddressGroup
                   from address in EmployeeAddressGroup.DefaultIfEmpty()
                   select new { employee, address }).ToList();