What's in your Ecto ChangesetHelpers module?


I’ve been noticing across my Elixir projects that use Ecto.Changeset that I have some common code between them. I usually have some extra validation functions, functions that conform some values (like cleaning up strings, eg: turning "null" into nil), and functions that help turn the changeset errors into a string readable by the end-user (like in a flash message on the web page if it’s a web app).

Here are some that I have:

  • full_sentence_errors - Turns an Ecto.Changeset with errors into a humanized string. This has lots of options like excluding keys and flattening embedded changesets’ errors.
  • update_cast_error_message - I found myself needing change Ecto’s casting error messages (something like "my_number_field is invalid") into something else like "my_number_field must be a number" .
  • ensure_uuid - Sometimes (like with Arc/Waffle) you need to have the ID field already present on the changeset so you can upload files while you’re inserting a record.
  • ensure_slug - Create a slug from another field, like “name”. This assumes you would have some unique constraints too on that field.
  • downcase_values - If string values are provided, then downcase them.
  • trim_values - if string values are provided, then trim them.
  • validate_url - Just validating that URI.parse(value) works.
  • validate_phone_number - I’ve used ExPhoneNumber for some stricter phone number validations.
  • normalize_phone_number - to keep user-input on phone numbers more consistent, like always using the national format
  • validate_required_if_any - if one of the fields is present, then require all the fields. For example, an address is optional but if you provide the state then you have to provide the rest of the address.
  • validate_required_any_of - One of the provided of fields is required.
  • validate_date_earlier_than - require a datetime field to be earlier than another field or a given datetime

Is there any interest in a library that includes these? Do you have any yourself that might be good to contribute?

(sidenote: ChangesetHelpers is a terrible name; if you have a suggestion on that I’m all ears)


For trimming, I ended up going with a custom ecto type because it’s such a common thing to want. So now just about every time I would use :string in my schema, I end up with a TrimmedString custom type that does the trimming.