I have following Group and Contact model in flask with Sql Alchemy ORM
group_contact = db.Table('group_contact',db.Column('group_id', db.Integer, db.ForeignKey('group.id')),db.Column('contact_id', db.Integer, db.ForeignKey('contact.id')),db.PrimaryKeyConstraint('group_id', 'contact_id')
)class Group(db.Model):id = db.Column(db.Integer, primary_key=True)name = db.Column(db.String(100))class Contact(db.Model):id = db.Column(db.Integer, primary_key=True)phone = db.Column(db.String(15), nullable=False, unique=True)groups = db.relationship("Group", secondary=group_contact, backref='contacts')
Now I need to query Contact with groups:
contacts = Contact.query.join(Group, Contact.groups).all()
for contact in contacts:print(contact.groups)
Here the problem is number of SQL query increases as number of contact increases when I execute above code.
Django ORM has prefetch_related() with queryset which does the following according to django docs.
prefetch_related, on the other hand, does a separate lookup for each relationship, and does the ‘joining’ in Python. This allows it to prefetch many-to-many and many-to-one objects, which cannot be done using select_related, in addition to the foreign key and one-to-one relationships that are supported by select_related.
Now I am trying to do the same thing with Sql Alchemy by the following code:
contacts = Contact.query.all()
contact_groups = group_contact.query.join(Group
).filter(group_contact.contact_id.in_([item.id for item in contacts]))
But this gives me this error:
AttributeError: 'Table' object has no attribute 'query'
How can I get prefetch_related like feature from django with SqlAlchemy?