Polymorphic_embed - polymorphic Embeds in Ecto

This seems to work the first time I select something. But if I then change my selection, it doesn’t actually change anything. Even in my handle_event I’m not seeing the updated selection.

Big frameworks like Rails and Django calls the relational non-embedded versions “polymorphic associations” as does Ecto so that is likely what most people would be searching for.

I really love this and often faced the problem. The reason I haven’t found this before is the naming. Isn’t that more of a (algebraic) sum-type than polymorphism?

You just need to manipulate the type field in the polymorphic field (by default __type__).

So, given a “type” field (of type string) you could try something along this for example:

<.input field={@form[:type]} type="select" label="Select type" name={@form[:my_polymorphic_field].name <> "[__type__]"}
          options={[{:sms, :sms}, {:email, :email}]} prompt="" />

At work we got stuck using the library to allow changing the type using a form. Is polymorphic_embed intended for this usecase? Or is the type meant to be chose once at creation time, and then stay fixed throughout its lifetime?

Edit: sorry, did not intend to make this a reply… it was meant to be a general question.

The module, PolymorphicEmbed.HTML.Form appears to be entirely outdated for forms in Phoenix 1.7.2 and above. I needed PolymorphicEmbed.HTML.Form.get_polymorphic_type/3 to render the UI properly so I rewrote it:

def get_polymorphic_type(%Phoenix.HTML.Form{} = form, schema, field) do
    module = PolymorphicEmbed.get_polymorphic_module(schema, field, form.params)
    PolymorphicEmbed.get_polymorphic_type(schema, field, module)
end

A tricky bug has been fixed where atoms were not persisted in the compilation files. The atoms specifying the types were converted into strings in the Ecto Type’s init/1 function at compile-time, and so as we only worked with the strings afterwards, the atoms were not persisted:
https://github.com/mathieuprog/polymorphic_embed/issues/59

Fixed in 3.0.3 thanks to the support of @LostKobrakai on Slack and the contribution of Alessio !

Version 3.0.0 has been released!

We now encourage the use of polymorphic_embeds_one/2 and polymorphic_embeds_many/2 macros to define your polymorphic embeds.

If you’re curious as to why: a field containing a polymorphic list of embeds defaulted to nil before version 3. To follow embeds_many/3 we should default to []. This can only be done by forcing the :default option of the field/3 to [] (ie we can’t configure this in the Type). I added the new macros in order to set these kind of defaults setting up the field for the polymorphic embeds.

Thanks to Alexandre @Matsa59 for his contribution which led to this update!

• Support for LiveView forms has been added thanks to the quality contribution of Mathias!

• Support for primary keys has been added

The latter may introduce breaking changes, therefore Polymoprhic Embed version has been bumped to 2.0.0

Migration from 1.x to 2.x is easy:

• Make sure that every existing polymorphic embedded_schema contains the setting @primary_key false

Just wanted to jump in and say thanks for this awesome library @mathieuprog

We have been using it for the last few months at my day job and it has been an absolute pleasure. Works well and reliably and the documentation is top-notch.