Add a more generic build_from method to external

[rogercampos]

the existing create_from does a lot of things, including a call to save(validate: false). This is a generic version that can be better adapted to your needs

[arnvald]

Hmm, I like the idea to have this method, but then can't we really reuse this method in create_from? We could call build_from there and just save the record in the end.