helpers for updating nested changesets

[woylie]

This is a proposal for the addition of some helper functions for manipulating nested changesets.

One common use case for changesets is as FormData for forms in Phoenix. With LiveView, we can easily build complex, dynamic, nested forms, but Ecto doesn't expose functionality for easily manipulating nested associations at the moment. I'm proposing the addition of four functions to Ecto.Changeset.

• append_at/3: appends a new item to an array field or has_many association at the given path
• insert_at/3: inserts a new item at a path/position
• update_at/3: updates a change or field at the given path
• delete_at/2: deletes an item at a given path/position

The path argument in all these functions would be a list of atoms (to reference fields) and integers (to reference the index in a list). For example, append_at(changeset, [:posts, 4, :comments], %Comment{}) would append a comment at root.posts[4].comments. delete_at(changeset, [:posts, 3]) would delete the post with index 3.

I sketched out a rough implementation for append_at/3 in this PR. Before I flesh this out to handle all cases and errors, I'd like to hear someone's thoughts on this effort.

[josevalim]

Thanks @woylie! I agree with it in principle but I am not sure how happy Ecto is going to be about reading the value and putting the same value back. So may I suggest you create a ecto_nested_changeset package to battle test those ideas out? I appreciate the ping!

[woylie]

Thanks @josevalim! I moved the code to https://github.com/woylie/ecto_nested_changeset. I'll let you know once I have a working version.

[josevalim]

Beautiful! Closing for this now!

[woylie]

Hi @josevalim, just pinging you to let you know that a first version has been released: https://github.com/woylie/ecto_nested_changeset

There is an example Phoenix application in the /example folder.

[josevalim]

Sweet, thanks for sharing!