My question is around Ecto.Changeset and the need to validate entire models, not just the passed in params. Basically, I’ve found a useful pattern is to write a set of validations; for a specific action; against the model after the params are filter; and after the params are applied. The first two items were awkward to do in rails 4 while the later easy. So if a model is loaded from the database, the passed in params in combination to the fields already set on the model (or perhaps in the session) are what are validated. Validating just the passed in params is also useful (eg. enforcing that the password was sent along with the sensitive account update request) but done less often.
Ecto.Changest is exciting because it decouples the changes from the model, however, most of the validations run only against the params, not the fields in the data after the params are applied. What I want is the option to validate_change, etc using not get_change nor really even get_field but just the data field after the params are filtered and cast. Obviously if the changes make the model invalid then the model won’t be saved (and one could image a copy of the un-modified struct along with the modified version anyways). Technically using get_field could work as well.
Rewriting new functions that apply the changes and then validate the model seem to not be in spirit with Ecto.Changeset and I wish there is a solution that could work with existing models and libraries that leverage it.
I am looking for thoughts around how these types of changes are meant to be handled in elixir (especially during a typical request to update a resource in Phoenix) and how that pattern can fit into this. Radical departures to what I am looking for are great to hear but having a specific answer is also appreciated.
