How to automatically reflect table relationships in SQLAlchemy or SqlSoup ORM? - sql

Question

How do I tell SQLAlchemy to automatically reflect basic Foreign Key references as references to other ORM objects and not integer fields?
In both SQLAlchemy and it's SqlSoup, table columns are reflected automatically and relations can be defined manually:
class User(Base):
__table__ = metadata.tables['users']
loan = relation(Loans)
...
You can define relationships on SqlSoup classes:
>>> db.users.relate('loans', db.loans)

Answer 1

Try this magic )
Works for simple FK relations, and without db schemes
from sqlalchemy import create_engine, MetaData
from sqlalchemy.orm import mapper, relation
engine = create_engine("sqlite://", echo=True)
engine.execute('''
create table foo (
id integer not null primary key,
x integer
)''')
engine.execute('''
create table bar (
id integer not null primary key,
foo_id integer,
FOREIGN KEY(foo_id) REFERENCES foo(id)
)''')
metadata = MetaData()
metadata.reflect(bind=engine)
MAPPERS = {
}
repr_name = lambda t: '%s%s' % (t[0].upper(), t[1:])
for table in metadata.tables:
cls = None
# 1. create class object
cls_name = repr_name(str(table))
exec("""class %s(object): pass""" % cls_name)
exec("""cls = %s""" % cls_name)
# 2. collect relations by FK
properties = {}
for c in metadata.tables[table].columns:
for fk in c.foreign_keys:
name = str(fk.column).split('.')[0]
properties.update({
name: relation(lambda: MAPPERS[repr_name(name)]),
})
# 3. map table to class object
mapper(cls, metadata.tables[table], properties=properties)
MAPPERS.update({cls_name: cls})
if __name__ == '__main__':
from sqlalchemy.orm import sessionmaker
print 'Mappers: '
for m in MAPPERS.values():
print m
session = sessionmaker(bind=engine)()
foo = Foo()
foo.x = 1
session.add(foo)
session.commit()
print session.query(Foo).all()
bar = Bar()
bar.foo = foo
session.add(bar)
session.commit()
print session.query(Bar).all()