[Sqlalchemy-tickets] [sqlalchemy] #1481: add doc snip for column-based m2m

[sqlalchemy <mi...@zz...>]

#1481: add doc snip for column-based m2m
---------------------------+------------------------------------------------
 Reporter:  zzzeek         |          Owner:  zzzeek               
     Type:  enhancement    |         Status:  new                  
 Priority:  medium         |      Milestone:  0.5.xx               
Component:  documentation  |       Severity:  trivial - <10 minutes
 Keywords:                 |   Status_field:  awaiting triage      
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 {{{
 Thanks for the help. By the way, I suggest adding this example to the
 documentation; I know it would have saved me a lot of head-banging. I
 suggest the following text tacked at the end of "SQL Expressions as
 Mapped Attributes" in "Mapper Configuration":

 For many-to-many relationships, use and_() to join the fields of the
 association table to both tables in a relation:

 mapper(Author, authors, properties={
     'books': relation(Book, secondary=book_authors,
 backref='authors'),
     'book_count': column_property(select([func.count(books.c.id)], and_
 (book_authors.c.author_id==authors.c.id,
 book_authors.c.book_id==books.c.id)).label('books_count'))
     })

 }}}

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Ticket URL: <http://www.sqlalchemy.org/trac/ticket/1481>
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