Phoenix Form Field For Array Model Data Type

Question

I'm using the amazing Phoenix Web Framework and trying to figure out how to create the form field(s) for a model with an array field.

Here is an example field from the model: field :grateful, {:array, :string}

I've tried generating the fields like this:

<%= inputs_for f, :grateful, fn fp -> %>
   <%= text_input fp, :grateful %>
<% end %>

But I get this error: could not generate inputs for :grateful from Motivation.DailyPost. Check the field exists and it is one of embeds_one, embeds_many, has_one, has_many, belongs_to or many_to_many

If I generate the field like this: <%= text_input fp, :grateful %> it generates a form field with a name of: daily_post[grateful] which actually won't work. I would need daily_post[grateful][].

The code below works, but loading the data after saving does not work. All array values are merged into one input field.

  <div class="form-group" id="grateful-group">
    <%= label f, :grateful, class: "control-label" %>
      <%= text_input f, :grateful, name: "daily_post[grateful][]" %>
    <%= error_tag f, :grateful %>
    <input type="button" class="btn btn-success" id="add-grateful" value="add" />
    <script>
      window.onload = () => {
        $('#add-grateful').click((e) => {
          $('<input type="text" name="daily_post[grateful][]" />').appendTo("#grateful-group");
        })
      }
    </script>
  </div>

How can I properly work with the array datatype in phoenix?

Thanks!

Answer 1

Ok I think I got it now. This is what I did:

defmodule Motivation.InputHelpers do
  use Phoenix.HTML

  def array_input(form, field, attr \\ []) do
    values = Phoenix.HTML.Form.input_value(form, field) || [""]
    id = Phoenix.HTML.Form.input_id(form,field)
    content_tag :ul, id: container_id(id), data: [index: Enum.count(values) ] do
      values
      |> Enum.with_index()
      |> Enum.map(fn {k, v} ->
        form_elements(form, field, k, v)
      end)
    end
  end

  def array_add_button(form, field) do
    id = Phoenix.HTML.Form.input_id(form,field)
    # {:safe, content}
    content = form_elements(form,field,"","__name__")
      |> safe_to_string
      # |> html_escape
    data = [
      prototype: content,
      container: container_id(id)
    ];
    link("Add", to: "#",data: data, class: "add-form-field")
  end

  defp form_elements(form, field, k ,v) do
    type = Phoenix.HTML.Form.input_type(form, field)
    id = Phoenix.HTML.Form.input_id(form,field)
    new_id = id <> "_#{v}"
    input_opts = [
      name: new_field_name(form,field),
      value: k,
      id: new_id
    ]
    content_tag :li do
      [
        apply(Phoenix.HTML.Form, type, [form, field, input_opts]),
        link("Remove", to: "#", data: [id: new_id], class: "remove-form-field")
      ]
    end
  end

  defp container_id(id), do: id <> "_container"

  defp new_field_name(form, field) do
    Phoenix.HTML.Form.input_name(form, field) <> "[]"
  end

end

I import that file into my web.ex, then I can print array fields like this:

<%= array_input f, :grateful %>

I can also print an add button for the field like this:

<%= array_add_button f, :grateful %>

To facilitate adding & removing fields I wrote this javascript:

window.onload = () => {
  const removeElement = ({target}) => {
    let el = document.getElementById(target.dataset.id);
    let li = el.parentNode;
    li.parentNode.removeChild(li);
  }
  Array.from(document.querySelectorAll(".remove-form-field"))
    .forEach(el => {
      el.onclick = (e) => {
        removeElement(e);
      }
    });
  Array.from(document.querySelectorAll(".add-form-field"))
    .forEach(el => {
      el.onclick = ({target}) => {
        let container = document.getElementById(target.dataset.container);
        let index = container.dataset.index;
        let newRow = target.dataset.prototype;
        container.insertAdjacentHTML('beforeend', newRow.replace(/__name__/g, index));
        container.dataset.index = parseInt(container.dataset.index) + 1;
        container.querySelectorAll('a.remove-form-field').forEach(el => {
          el.onclick = (e) => {
            removeElement(e);
          }
        })
      }
    });
}