How to clone a SQLAlchemy object with new primary key

Question

I want to clone a SQLAlchemy object:

I tried:

product_obj = products.all()[0] #here products is service name

product_obj.product_uid = 'soemthing' #here product_uid is the pk of product model

products.save(product_obj)

but it just updates the old object.

Here is the code of products.save function:

class Service(object):

        __model__ = None

       def save(self, model):
            self._isinstance(model)
            db.session.add(model)
            db.session.commit()
            return model

Answer 1

This should work:

product_obj = products.all()[0]

db.session.expunge(product_obj)  # expunge the object from session
make_transient(product_obj)  # http://docs.sqlalchemy.org/en/rel_1_1/orm/session_api.html#sqlalchemy.orm.session.make_transient

product_obj.product_uid = 'something'
db.session.add(product_obj)

Answer 2

For sqlalchemy 1.3 I ended up using a helper function.

1. It copies all the non-primary-key columns from the input model to a new model instance.
2. It allows you to pass data directly as keyword arguments.
3. It leaves the original model object unmodified.

def clone_model(model, **kwargs):
    """Clone an arbitrary sqlalchemy model object without its primary key values."""
    # Ensure the model’s data is loaded before copying.
    model.id

    table = model.__table__
    non_pk_columns = [k for k in table.columns.keys() if k not in table.primary_key.columns.keys()]
    data = {c: getattr(model, c) for c in non_pk_columns}
    data.update(kwargs)

    clone = model.__class__(**data)
    db.session.add(clone)
    db.session.commit()
    return clone

With this function you can solve the above problem using:

product_obj = products.all()[0]  # Get the product from somewhere.
cloned_product_obj = clone_model(product_obj, product_uid='something')

Depending on your use-case you might want to remove the call to db.session.commit() from this function.

---

This answer is based on https://stackoverflow.com/a/13752442/769486 (How to get a model’s columns?) and How do I get the name of an SQLAlchemy object's primary key? (How do I get a model’s primary keys?).

Answer 3

One possible approach is to use dictalchemy, which extends SQLAlchemy:

Dictalchemy adds utils.asdict() and utils.fromdict() methods to SQLAlchemy models.

Example:

new_instance = InstanceModel(**old_instance.asdict())

Answer 4

This method will clone any sqlalchemy db object. Add it to your model's class. Please note the the id of the new object will be created during commit (see comment):

def clone(self):
    d = dict(self.__dict__)
    d.pop("id") # get rid of id
    d.pop("_sa_instance_state") # get rid of SQLAlchemy special attr
    copy = self.__class__(**d)
    db.session.add(copy)
    # db.session.commit() if you need the id immediately
    return copy