I have a postgres database that looks something like this:

      Table "public.entities"Column     |            Type             |                   Modifiers                    
---------------+-----------------------------+------------------------------------------------id            | bigint                      | not null default nextval('guid_seq'::regclass)type_id       | smallint                    | not nullname          | character varying           | 
Indexes:"entities_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:"entities_parent_id_fkey" FOREIGN KEY (parent_id) REFERENCES entities(id)"entities_type_id_fkey" FOREIGN KEY (type_id) REFERENCES entity_types(id)
Referenced by:TABLE "posts" CONSTRAINT "posts_id_fkey" FOREIGN KEY (id) REFERENCES entities(id)TABLE "posts" CONSTRAINT "posts_subject_1_fkey" FOREIGN KEY (subject_1) REFERENCES entities(id)TABLE "posts" CONSTRAINT "posts_subject_2_fkey" FOREIGN KEY (subject_2) REFERENCES entities(id)Table "public.posts"Column   |  Type  | Modifiers 
-----------+--------+-----------id        | bigint | not nullposter_id | bigint | subject_1 | bigint | not null subject_2 | bigint | not null 
Indexes:"posts_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:"posts_id_fkey" FOREIGN KEY (id) REFERENCES entities(id)"posts_poster_id_fkey" FOREIGN KEY (poster_id) REFERENCES users(id)"posts_subject_1_fkey" FOREIGN KEY (subject_1) REFERENCES entities(id)"posts_subject_2_fkey" FOREIGN KEY (subject_2) REFERENCES entities(id)

I'm trying to figure out how to define the orm object for "posts" to include all 3 of the foreign keys. Notice only id is a primary key. The others are just relationships between posts and entities that are not to be pk'd.

class PostModel(EntitiesModel):__tablename__ = 'posts'id = db.Column(db.BigInteger, db.ForeignKey(EntitiesModel.id), primary_key=True, nullable=False)poster_id = db.Column(db.BigInteger, db.ForeignKey(UserModel.id), nullable=False)subject_1 = db.Column(db.BigInteger, db.ForeignKey(EntitiesModel.id), nullable=False)subject_2 = db.Column(db.BigInteger, db.ForeignKey(EntitiesModel.id), nullable=False)

I've tried fiddling with it a bit, and besides disabling the foreign keys on subject_1 I can't seem to come up with a solution that doesn't result in this error:

AmbiguousForeignKeysError: Can't determine join between 'entities' and 'posts'; tables have more than one foreign key constraint relationship between them. Please specify the 'onclause' of this join explicitly.

Any thoughts?

It's not completely clear what exactly is causing the problem since you omitted the most important part -- code that throws that exception but if adding relationship properties to class PostModel throws that try to add foreign_keys parameter to relationship call as the following:

class PostModel(...):# ...subject1_id = Column(db.Column(db.BigInteger, db.ForeignKey(EntitiesModel.id), nullable=False)subject2_id = Column(db.Column(db.BigInteger, db.ForeignKey(EntitiesModel.id), nullable=False)subject1 = relationship(EntitiesModel, foreign_keys=subject1_id)subject2 = relationship(EntitiesModel, foreign_keys=subject2_id)