SQLAlchemy: get relationships from a db.Model

Question

I need to get a list of a model's properties which are actually relationships (that is, they were created by relationship()).

Say I have a model Foo in a models:

class Thing(db.Model):
    id = db.Column(...)
    bar_id = db.Column(...)
    foo_id = db.Column(...)
    foo = db.relationship('Foo')
    bar = db.relationship('Bar')

Later on, I want to take models.Thing and get a list of relationship-properties, that is ['foo', 'bar'].

Currently I'm checking every attribute indicated by dir(models.Thing) that happens to be of type sqlalchemy.orm.attributes.InstrumentedAttribute for the class of its property attribute — which can be either a ColumnProperty or RelationshipProperty. This does the job but I was wondering if there's another way.

I could probably just find all attributes ending in _id and derive the relationship name, but this could break for some cases.

How about setting a __relationships__ = ['foo', 'bar']?

Or is there something built into SQLAlchemy to help me out?

Answer 1

There is indeed - take a look at sqlalchemy.inspection.inspect. Calling inspect on a mapped class (for example, your Thing class) will return a Mapper, which has a relationships attribute that is dict like:

from sqlalchemy.inspection import inspect

thing_relations = inspect(Thing).relationships.items()

Answer 2

You just need to use the inspect module from sqlalchemy

from sqlalchemy import inspect

i = inspect(model)
i.relationships

If you need the class of each referred model you can do:

referred_classes = [r.mapper.class_ for r in i.relationships]

Answer 3

Instead of using inspect you can also use

model.__mapper__.relationships