Phoenix LiveView Nested Associations Form

Question

I'm experimenting with Phoenix 1.6 and LiveView, and trying to get my nested form/models to work as expected.

I have a schema with something like: Parent , Child , where Parent has_many Children // Child belongs_to parent.

• I have a LiveView component with a form for Parent, which works well as expected.
• I render Parent.children with inputs_for, and the initial render (such for rendering Children that are already in the database) works fine.

I want to have something like an Add Child button, which will render another Child model in my form in the inputs_for block, that I can make changes to, and eventually submit.

I've tried a handful of things such as https://fullstackphoenix.com/tutorials/nested-model-forms-with-phoenix-liveview , but they either don't seem to work, or seem a bit outdated (referencing things that don't exist for me). The documentation helps a little bit, but doesn't seem to connect the Ecto bits with the LiveView bits that I'm looking for very well. Does anyone have thoughts/advice on the best way to achieve what I'm looking for? (I'm also a bit newer to Elixir/Phoenix/Ecto, so there may be things that I'm overlooking)

Answer 1

I don't know if you're still struggling with this but I made it work some time ago. I was working on some e-commerce application prototype and found the same post you shared.

Here's a form_component example that uses the variants concept. If you use Phoenix 1.5 you can look a few commits back before the migration to .heex happened.

I could give you some more advice if you share a bit of code where the problem resides.

Answer 2

This is a basic example.

     <.icon phx-click="add_row" phx-value-id={f.data.id}
    ...
    
    
    def handle_event("add_row", %{"id" => id}, socket) do
        %{changeset: changeset, parent: parent} = socket.assigns
        l = length(parent.childs)
        new_child = %Child{order: l, parent_id: id}
    
        childs =
          changeset.changes
          |> Map.get(:childs, parent.childs)
          |> Enum.concat([new_child])
    
        parent = Map.put(parent, :childs, childs)
    
        {:noreply,
         socket
         |> update(:changeset, fn changeset ->
           Ecto.Changeset.put_assoc(changeset, :childs, childs)
         end)
         |> assign(:parent, parent)}
      end