如何使用新主键克隆sqlalchemy数据库对象

Question

我想克隆一个sqlalchemy对象:

我试过了

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)

它只是更新old_object

这是products.save函数的代码

class Service(object):

        __model__ = None

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

Answer 1

这应该工作:

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

一种可能的方法是使用dictalchemy：

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

Answer 3

此方法将克隆任何 sqlalchemy 数据库对象。将其添加到您的模型的类中。请注意，新对象的 id 将在提交期间创建（请参阅评论）：

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

Answer 4

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]
    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 /sf/answers/962670971/ (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?).