Select value from grandchildren

问题

I have the following table structure:

I want to select:

• all TableA entries + the Identifier column from Table C that have:
  • a special value in TableBType ("TableBTypeValue")
  • a special value in TableCType ("TableCTypeValue")

The problem that I have is that the linq queries seem to fail when there are TableA entries that have no TableB entry or if there are TableB entries without a TableC (TableBType and TableCType is mandatory so they don't have that problem).

With SQL this would not be a big problem, but as I am new to linq I could not find the correct way to create this query.

回答1:

I think this is what you are looking for:

from c in db.TableC
where c.TableCType == TableCTypeValue
join b in db.TableB on c.TableBId equals b.Id
where b.TableBType == TableBTypeValue
join a in db.TableA on b.TableAId equals a.Id
select new { a, c.Identifier };

Hope it helps.

来源：https://stackoverflow.com/questions/11925676/select-value-from-grandchildren