Suppose I have a mapped class User
, mapped to a tables of the same name, and a column "age" for his age. I'm now interested in the following problem:
In the course of my application, there emerge two queries:
q1 = session.query(User).filter(lots of conditions)
q2 = session.query(User).filter(lots of other conditions)
I now want to "join" q2 onto q1 upon the condition that they have the same age. But I have no idea of how this might work. I tried the following without success:
q1.join(q2.subquery(), q1.age==q2.age) # the query doesn't hold the columns of the queried class
q1.join(Age).join(q2.subquery()) # Works only if age is a relationship with mapped class Age
My closest calls were something like this:
a1 = aliased(User)
a2 = aliased(User)
q1 = session.query(a1)
q2 = session.query(a2)
s = q2.subquery()
q1.join(s, a1.age==a2.age).all()
>>> sqlalchemy.exc.OperationalError: (OperationalError) no such column: user_2.age 'SELECT user_1.id AS user_1_id, user_1.name AS user_1_name, user_1.age AS user_1_age \nFROM user AS user_1 JOIN (SELECT user_2.id AS id, user_2.name AS name, user_2.age AS age \nFROM user AS user_2) AS anon_1 ON user_1.age = user_2.age' ()
Any ideas about how to make this run?
After fiddling around and reading answers to questions about subqueries, I managed to find a solution. Instead of the last, offending line, put:
q1.join(s, a1.age==s.columns.age).all()
That way, the on-clause becomes ON user_1.age = anon_1.age
, which is what we want.
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.