使用sqlalchemy时如何进行高级联接？

Question

Could someone show me how I can accomplish this in sqlalchemy?

SELECT
  *
FROM animals a
INNER JOIN species s
  ON (s.species_id=a.id AND s.type='mammals')
LIMIT 1;

I have tried many different things, but I keep getting weird results. If someone please help me with this I would greatly appreciate this.

Some code I have done:

result = session.query(Animal).\
    join((Species, (Species.species_id==Animal.id)), (Species, (Species.type=='mammals')))
    .all()

This of course gives me:

SELECT
      *
    FROM animals
    INNER JOIN species
      ON (species.species_id=animals.id)
    INNER JOIN species
      ON (AND species.type='mammals')
    LIMIT 1;

But this is not exactly what I want.

Thanks in advance.

-e

Answer 1

You just need and_ :

from sqlalchemy.sql import and_

result = session.query(Animal).join(Species, and_(
    Species.species_id == Animal.id,
    Species.type == 'mammals',
)).all()

EDIT: this is using the "two-argument calling form" of join available in SQLAlchemy 0.7 and later.