Question

I have another quick question about SQLAlchemy.

If I have added a query_property [1] field in my SQLAlchemy Table class, is it possible to narrow down the SELECTed fields?

Here is what I mean.

Suppose my class Comments has this:

class Comments:
    query = Session.query_property()
    ...

Then if I do the following:

>>> print Session.query(Comment)                      

Then SQLAlchemy generates the following query which includes ALL the columns in my comments table:

SELECT comments.comment_id AS comments_comment_id,
       comments.comment    AS comments_comment
       ... more columns ...
FROM comments

But I want to narrow down this query and select only (let’s say) the comment field as in the following construct:

>>> print Session.query(Comment.comment)   
SELECT comments.comment AS comments_comment 
FROM comments

Is it possible to do this via Comment.query construct?

I tried the following but it didn’t work:

>>> print Comment.query(Comment.comment)                
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
TypeError: 'Query' object is not callable

Please help me with an advice.

Thanks, Boda Cydo.

[1] http://www.sqlalchemy.org/docs/reference/orm/sessions.html#sqlalchemy.orm.scoping.ScopedSession.query_property

Answer 1

Try using query.values(Comment.comment). Note that it returns generator, not modified query, so this method should called last after applying all filters.