Cast error when filtering field of type :id with a string containing non-numeric characters.

[linusdm]

Hey!

I'm using Flop for the first time, and I'm having a question. I'm trying to filter a field of type :id. The Flop.Schema behaviour is derived and the :my_id_field field is marked as filterable. I use the <.Flop.Phoenix.filter_fields ...> function component, with the field attribute set to [my_id_field: [op: :==, ...]. This goes well when I enter some digits into the generated inputs. But when I enter a random string (so not only numeric input), an error is raised:

** (Ecto.Query.CastError) deps/flop/lib/flop/builder.ex:148: value `"abc"` in `where` cannot be cast to type :id in query:

from l0 in MyApp.SomeStruct,
  where: ^true and l0.my_id_field == ^"abc",
  ...

I'm using the Flop.validate_and_run/3 function, so I would expect that this situation would have generated a validation error. But no validation is triggered, and the query is executed, resulting in the above error. Maybe my expectation is wrong, and there is no validation for these kinds of type checks.

But now I'm unsure how to proceed. I've made a custom filter that uses Ecto.Type.cast(:id, value) to determine if the form value can be cast to the :id type. If that's possible, I use the casted value to add a where clause (a bit like in the example of custom filters). If it's not, I add false as a where condition, to make sure no results are shown (after all, nothing could possibily match with this input). But it feels a bit strange this way, and I might prefer an earlier validation error in this case, to indicate the user that the filled in value is actually not correct (should be an integer/id, instead of a string).

Any suggestions are welcome! I'm enjoying the library. But since I'm new to it, maybe my expectations are wrong...

[linusdm]

This issue is probably related: #286

[woylie]

You found the right issue. Right now, Flop relies on Ecto when it comes to filter values. Until 0.19, there was no way to tell Flop the Ecto type for join fields. Now that that is in place, and after adding the ecto_type option to alias fields as well, we have all the necessary information to validate filter values before they are passed to Ecto. Until that has been implemented, I see two workarounds. One would be the solution with custom fields you described, which admittedly is a bit cumbersome, and the other would be to catch the CastError:

def list_pets(params \\ %{}) do
  Flop.validate_and_run(Pet, params, for: Pet)
rescue
  Ecto.Query.CastError -> {:ok, {[], %Flop.Meta{}}}
end

You'll need to set the meta fields yourself in this case, though.

[linusdm]

Ok, thanks for the double check and the alternative!