Entity Framework with Multiple Joins and Subquery - sql

Question

I have a complex query with multiple left joins and subqueries which I need to implement in Entify Framework. I've received the monster SQL and
my goal is to do it on a elegant way with EF. The query consumes multiple tables and creates a "WITH" subquery on top which
is included in the joins later. I've done a first approach with EF but when I inspect the output that EF sends to the DB, inner joins are sent when
I am expecting LEFT JOINs.
A summary of the SQL follows:
WITH SUB_QUERY
AS ( SELECT FIELD_A,
FIELD_B,
FIELD_C,
MAX (FIELD_D) MAX_FIELD_D
FROM TABLE_X
WHERE SOME FIELD_A = 'WHATEVER'
GROUP BY FIELD_A, FIELD_B, FIELD_C)
SELECT C.FIELD_A,
C.FIELD_B,
B.FIELD_X,
D.FIELD_S,
E.FIELD_J,
F.FIELD_Y
FROM TABLE_A A
LEFT JOIN SUB_QUERY B
ON A.FIELD_C = B.FIELD_C
LEFT JOIN TABLE_C C
ON B.FIELD_A = C.FIELD_A
LEFT JOIN TABLE_D D
ON A.FIELD_C = D.FIELD_C
LEFT JOIN TABLE_E E
ON A.FIELD_X = E.FIELD_X
LEFT JOIN TABLE_F F
ON A.FIELD_W = F.FIELD_W
WHERE A.FIELD_H = D.FIELD_H
AND A.FIELD_D = B.MAX_FIELD_D
As you see, a subquery on top filters and groups some data to be consumed in a join below. Then all the joins take place
and some fields are taken from different tables as the output of the query.
Which approach would you recommend me to accomplish this task? I've tried different approaches and no one of them works (either retrieve nothing, or many more rows than the SQL query on the DB, etc..)
Please note that the Domain Model in Entity Framework is properly setup: Primary Keys, collections, nested objects etc.. so I believe some of these
joins are not even required because my EF entities contain already references to the child collections and parent objects (navigation properties).
Thanks a lot!!

Answer 1

if you really need a left join you should mode the where condition related to a left joined table in the proper on clause
FROM TABLE_A A
LEFT JOIN SUB_QUERY B
ON A.FIELD_C = B.FIELD_C
LEFT JOIN TABLE_C C
ON B.FIELD_A = C.FIELD_A
LEFT JOIN TABLE_D D
ON A.FIELD_C = D.FIELD_C AND A.FIELD_D = B.MAX_FIELD_D
LEFT JOIN TABLE_E E
ON A.FIELD_X = E.FIELD_X
LEFT JOIN TABLE_F F
ON A.FIELD_W = F.FIELD_W
the use of a left join table column in where force the relation to work as a INNER JOIN