How do you perform a left outer join using linq extension methods

Question

Assuming I have a left outer join as such:

from f in Foo
join b in Bar on f.Foo_Id equals b.Foo_Id into g
from result in g.DefaultIfEmpty()
select new { Foo          


        

Answer 1

Whilst the accepted answer works and is good for Linq to Objects it bugged me that the SQL query isn't just a straight Left Outer Join.

The following code relies on the LinkKit Project that allows you to pass expressions and invoke them to your query.

static IQueryable LeftOuterJoin(
     this IQueryable source, 
     IQueryable inner, 
     Expression> sourceKey, 
     Expression> innerKey, 
     Expression> result
    ) {
    return from a in source.AsExpandable()
            join b in inner on sourceKey.Invoke(a) equals innerKey.Invoke(b) into c
            from d in c.DefaultIfEmpty()
            select result.Invoke(a,d);
}

It can be used as follows

Table1.LeftOuterJoin(Table2, x => x.Key1, x => x.Key2, (x,y) => new { x,y});