Is there a plan to support custom loading for embedded types?

Questions / Help
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1

Custom types do not use load/dump when embedded.

Then may use dump if they define embed_as to return :dump, but there is no way to use load or any other mechanism then cast when loading data.

  1. Is there a good reason for this design? The asymmetry in dumping / loading is a bit odd to me.

Moreover the fact that cast has to be called when loading from the DB can be quite inconvenient. While returning :error when casting user data (e.g. from a form) is very useful, if I have invalid data stored in my DB then returning :error result in a raised exception, which is blocking. Moreover, thereā€™s no way to know within cast if Iā€™m loading from the DB or casting user data.

  1. Documentation for load is very misleading, e.g.

There are two situations where this callback is called:

  1. When casting values by Ecto.Changeset
  2. When passing arguments to Ecto.Query

Clearly, this is incomplete and there is an extra situation ā€œ3. When loading data in an embedded schemaā€.

I can propose a PR but would appreciate to know if thereā€™s every a plan to support custom loading for embedded types.

Thank you

2 Likes
2

Maybe try posting this on the Ecto dev group as well.

3

We can always add a new value to em embed_as, we just need to understand the use case. The reason it was designed like this is because most embedding is done as JSON, which is a lossy format. And PRs to improve the docs are always welcome.

4

Thank you. I went another way for now, so Iā€™m not 100% confident about my usecase :sweat_smile:. I created a PR for the doc, thanks :heart: