I have tableA and tableB.
I would like to perform left join using lambda expression. This is the equal sql statement:
SELECT *
FROM tableA A
LEFT JOIN tableB B ON A.userId=B.userId
How can I do that using lambda expression?
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possible duplicate of How do you perform a left outer join using linq extension methodsLadislav Mrnka– Ladislav Mrnka2011-07-12 16:03:36 +00:00Commented Jul 12, 2011 at 16:03
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1 Answer
It's usually an error to use an explicit join in LINQ to Entities.
Instead, use the navigation properties:
var q = Context.TableAs.Select(a => new { a.Foo, a.TableB.Bar });
LINQ to Entities will coalesce null references. So if a.TableB is null for some record in TableAs, then a.TableB.Bar will return null instead of giving you a null reference exception. So it behaves like a SQL LEFT JOIN
5 Comments
Craig Stuntz
@Naor: Usually, the right thing to do is to add them. You should use explicit
joins mostly only if you can't add them for some reason.Craig Stuntz
@Naor: Like I said, mostly, you don't. You haven't yet convinced me that you have a good reason to omit navigations. Navigations are the right way to relate entities.
Naor
@Craig Stuntz: What about the desire to learn? How can I do left joins in lambda syntax?
Craig Stuntz
@Naor: That's a different question. You asked how to do it with L2E. The right way to do it in L2E is to use navigations. You want to do it in L2O, then you can use
Join() with a DefaultIfEmpty() on the "right" sequence. But don't do that for L2E, normally.
Tod
I have inherited a db that joins several tables without using any keys. (Before anyone weighs in with comments about that - I already know and as soon as I can replace the POS I will, but atm I can't.) And I can't create Navigations without them, so I have to do joins in code, and my personal preference is to use Lambda, in C# it makes more sense to me.