How to handle optional nested input with Phoenix framework? - phoenix-framework

Question

Phoenix nested form input via optional "inputs_for" is resulting in a map in the controller that fails validation. So for example, a post has comments. If I want to add a comment for a post when the post is created, the nested form would look like:
<%= form_for #changeset, #action, fn p -> %>
<%= text_input p, :body %>
<%= inputs_for p, :comments, fn c -> %>
<%= text_input c, :body %>
<% end %>
<% end %>
I fill in the post body but don't add anything for the comments this time around. That will give us the params["post"] map in the controller of
%{
"body" => "My post",
%{"comments" => %{"0" => %{"body" => ""}}
}
However, the comments are "optional". So, the validation done for comments will fail because there is a body but it is empty.
The question then is how do we remove/scrub comments if it is empty but keep it if it has some value? Scrubbing of params "post" does not seem to be doing the trick.

Answer 1

I guess you will have to write your own scrub_comments function plug that will remove empty comments from comments map and eventually remove comments if it is empty.

Answer 2

Here is the kind of approach Chris mentions. The below is modified from my working version to work with posts and comments, and is untested, but should at least show the approach.
A helper module:
defmodule MyappWeb.Helpers do
alias MyappWeb.Post
def filter_post_params(%Plug.Conn{:params => %{"post" => %{"comments" => _}}} = conn, _opts) do
filtered_params =
conn.params
|> get_in(["post"])
|> Enum.reject(fn({_, x}) -> match?(%{"comments" => nil}, x) end)
|> Enum.into(%{})
new_params = put_in(conn.params, ["post"], filtered_params)
%Plug.Conn{conn | params: new_params}
end
def filter_post_params(%Plug.Conn{} = conn, _opts), do: conn
end
The controller, using Phoenix's scrub_params plug and our filter_post_params plug from above:
defmodule MyappWeb.PostController do
use MyappWeb, :controller
alias Myapp.Post
plug :scrub_params, "post" when action in [:create, :update]
plug :filter_post_params when action in [:create, :update]
# ...
end