Question
How to write sub queries like these in EF?
select * from table1 where col1 in (select col1 from table2 where col2 = 'xyz')
or
select * from table1 where col1 not in (select col1 from table2 where col2 = 'xyz')
I tried something like these
from t1 in table1
where (from t2 in table2 where col2 = 'xyz' select t2.col1).Contains(t1.col1)
select t1
and
from t1 in table1
where !(from t2 in table2 where col2 = 'xyz' select t2.col1).Contains(t1.col1)
select t1
these queries are working fine LinqPad or Linq to Sql
Popular Answer
This type of subquery can be flattened to a join, which is the way I would choose to write it here:
SQL Version:
SELECT t1.col1, t1.col2, t1.col3, ...
FROM table1 t1
INNER JOIN table2 t2
ON t1.col1 = t2.col1
WHERE t2.col2 = 'xyz'
Linq Version:
var query =
from t1 in context.Table1
where t1.AssociationToTable2.Col2 == "xyz"
select new { t1.Col1, t1.Col2, ... };
Where AssociationToTable2 is the relationship property - it does the join automatically. Or, if you don't have a relationship:
var query =
from t1 in context.Table1
join t2 in context.Table2
on t1.Col1 equals t2.Col1
where t2.Col2 == "xyz"
select new { t1.Col1, t1.Col2, ... };
You can adapt these accordingly for NOT IN, although I'd recommend never to use NOT IN if you can avoid it - performance will sink and it almost always implies an error in design.
If you absolutely must do it the "IN" way, I suggest going over the answers in this question.
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