Question

I am trying to convert following SQL query to linq;

select Or.Amount, Usr.Name, Usr.Email
from [order] as Or
left join vw_AllUsers as Usr on Usr.UserId = Or.UserId and Usr.RoleName <> 'Admin'

I couldn’t find a way to use equal and not equal in the same join..
If Usr.RoleName <> ‘Admin’ was Usr.RoleName = ‘Admin’, the linq statement could be written like that

var result =  from Or in context.orders
              join Usr in context.vw_AllUsers on 
              new { userid = Or.UserId, role = "Admin"}
              equals
              new { userid = Usr.UserId, role = Usr.RoleName}
              select ........

or i can handle it in where part of the linq to get same result, as follows

where !Usr.RoleName.Equals("Admin")

but is it possible to handle this in join part of the linq ?

Thanks in advance

Answer 1

LINQ only supports equality joins, there’s not a way to use a different operator in the join itself.

As you point out, you can just use a where statement for the same effect. If you didn’t have an equality comparison to join on, you can use multiple from clauses.

From MSDN:

The equals operator

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A join clause performs an equijoin. In other words, you can only base matches on the equality of two keys. Other types of comparisons such as "greater than" or "not equals" are not supported. To make clear that all joins are equijoins, the join clause uses the equals keyword instead of the == operator. The equals keyword can only be used in a join clause and it differs from the == operator in one important way. With equals, the left key consumes the outer source sequence, and the right key consumes the inner source. The outer source is only in scope on the left side of equals and the inner source sequence is only in scope on the right side.

Non-Equijoins

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You can perform non-equijoins, cross joins, and other custom join operations by using multiple from clauses to introduce new sequences independently into a query. For more information, see How to: Perform Custom Join Operations (C# Programming Guide).