Flask-SQLAlchemy连接是否可以从一个表中选择所有列，并从另一个表中指定一些列？

Question

I'm doing a join of two tables and want to select all the columns from one and only some from another. I feel like I'm close, but it's not quite returning what I want. I have an advertisement table and a coupon table in where they have a 1 to 1 relationship.

I have called a query on the db model like so:

result = Advertisement.query.join(Coupon, 
Advertisement.id==Coupon.id).filter(Advertisement.date==Coupon.date, 
Advertisement.id==12345).add_columns(Coupon.discount, 
Coupon.expiry_date)

What I want to get back is all the columns from Advertisement and the two from Coupon. My understanding was that add_columns would do this, but I only get back the two from Coupon and nothing from Advertisement. While if I remove add_columns I get back all from Advertisement but nothing from Coupon.

Do I have to declare the table relationship in the class? I know what the query should look like in sql, but I'm at a bit of a loss here. If the information I gave isn't clear enough, let me know and I can try to elaborate further, thanks.

Answer 1

You can do it as follows:

result = session.query(Advertisement, Coupon.discount, Coupon.expiry_date).filter(
   Advertisement.id==Coupon.id, 
   Advertisement.date==Coupon.date, 
   Advertisement.id==12345
)