Question

I have several queries with 2 from clauses that look like this:

var TheResult = from a in MyDC.Table1
                from b in MyDC.Table2
                where a.SomeCol == b.SomeOtherCol
                select new MyModel() {....}

I’m concerned that this syntax is creating a cartesian join and I want to rewrite it with join syntax with only one from clause. My question is this: how should I determine which table should I put in the from clause?

Thanks.

Edit: the t-sql generated by the query starts with SELECT COALESCE(( is that a good/bad thing?

Answer 1

You can rewrite this into a JOIN pretty easily:

var result = from a in MyDC.Table1
             join b in MyDC.Table2 on a.SomeCol equals b.SomeOtherCol
             select new MyModel() { SomeProp = a.SomeCol, SomeProp2 = b.SomeCol }

Or if you want a left join:

var result = from a in MyDC.Table1
             join b in MyDC.Table2 on a.SomeCol equals b.SomeOtherCol
             into myGroup
             from m in myGroup.DefaultIfEmpty()
             select new MyModel() { SomeProp = a.SomeCol, SomeProp2 = m.SomeCol }