Inputs_for nested form error: construction of binary failed: segment 1 of type 'binary': expected a binary but got: nil

Phoenix Forum Questions / Help
,
1

I’m attempting to create a nested form with duplicate inputs for two separate ticket holders. I’m using the <.simple_form> in LiveView, and everything I’ve seen is using different syntax (i.e. <% as opposed to <.)

I have this form working:

<.simple_form :let={f} for={%{tickets: []}}>
           <.input
            field={f[:text]}
            type="text" label="Enter text:"
            autocomplete="text"
            placeholder="Enter text" />
          <.input
            field={f[:option_id]}
            type="select"
            label="Choose your option:"
            options={Enum.map(options, fn option -> {option.name, option.id} end)}
          />
          <.input
            field={f[:date]}
            type="date"
            label="Choose a date:"
          />
          <.input
            field={f[:time]}
            type="time"
            label="Choose a time:"
          />
          <div class="flex gap-2">
            <div class="w-2/3">
            <.input
              field={f[:weight]}
              type="number"
              label="Weight"
              min="0"
            />
            </div>
            <div class="w-1/3 mt-1">
            <.input
              field={f[:weight_unit]}
              type="select"
              label="Unit"
              options={Enum.map(weight_units, fn weight -> weight.unit end)}
            />
            </div>
          </div>
          <:actions>
            <.button button_type="booking">Continue</.button>
          </:actions>
</.simple_form>

however when I try to add this at the top of the form to test (from the Phoenix docs):

<.inputs_for :let={fp} field={f[:tickets]}>
  <.input field={fp[:name]} type="text" />
</.inputs_for>

I receive this error:

construction of binary failed: segment 1 of type 'binary': expected a binary but got: nil

with this stack trace:

id = to_string(id || form.id <> "_#{field}")

Any idea on how to create a duplicate nested form of the current simple form with a nested inputs_for? Thanks!

1 Like
2

Not sure what could be the issue. I tried to reproduced it on my end and everything is working fine. See the code below:

Schemas

defmodule MyApp.Shop.ProductCategory do
  use Ecto.Schema
  import Ecto.Changeset

  schema "product_categories" do
    field(:name, :string)

    timestamps()
  end

  @doc false
  def changeset(product_category, attrs) do
    product_category
    |> cast(attrs, [:name])
    |> validate_required([:name])
    |> unique_constraint(:name)
  end
end

defmodule MyApp.Shop.Product do
  use Ecto.Schema
  import Ecto.Changeset

  schema "products" do
    field(:name, :string)
    field(:price, :decimal)
    belongs_to(:product_category, MyApp.Shop.ProductCategory)
    timestamps()
  end

  @doc false
  def changeset(product, attrs) do
    product
    |> cast(attrs, [:name, :price])
    |> validate_required([:name, :price])
    |> cast_assoc(:product_category)
  end
end

And then in my Form:

.simple_form
        for={@form}
        id="product-form"
        phx-target={@myself}
        phx-change="validate"
        phx-submit="save"
      >
        <.input field={@form[:name]} type="text" label="Name" />
        <.input field={@form[:price]} type="number" label="Price" step="any" />

        <.inputs_for :let={category_form} field={@form[:product_category]}>
          <.input type="text" field={category_form[:name]} label="category" />
        </.inputs_for>

        <:actions>
          <.button phx-disable-with="Saving...">Save Product</.button>
        </:actions>
      </.simple_form>

Am on LiveView 0.18.18 and Phoenix 1.7.2. Perhaps can you try to update the Phoenix and LiveView?

3

When you pass a map to to_form/1, it assumes said map contains the form parameters, which are expected to have string keys.

Maybe try string key for the map?

4

I do have those same LiveView and Phoenix versions. When I implemented your form, I got the following error:

key :form not found in: %{__changed__: %{flash: true, id: true}

with this stacktrace

<.simple_form
        for={@form}
        id="product-form"
        phx-target={@myself}
        phx-change="validate"
        phx-submit="save"
      >
5

You can use to_form(map, id: …), but the support for map based nested forms is not great. E.g. there’s no way to pass errors to nested inputs.

6

Im experiencing the same issue right now. Have you discovered a solution?

7

JK passing the as option to to_form fixed everything for me. For example:

to_form(%{
    "name" => "birthday.png",
    "meta" => %{byte_size: 1000, location: "path/to/file"} 
}, as: "image")
1 Like
8

this worked for me as well, thanks

9

I encountered the same issue and only managed to make it work when
I defined the form_data

form_data = %{
    "nested_field" => %{
        "1" => %{
          "subfield1" => "value 1.1",
        },
        "2" => %{
          "subfield1" => "value 2.1",
        }
    }
} |> to_form(id: "nested_form")

and used inputs_for with as containing field name and default containing empty list.

<.form :let={f} for={@form_data}>
  <.inputs_for :let={nf} field={f[:nested_field]} as={:nested_field} default={[]}>
    <.input field={nf[:subfield1]} type="text"/>
  </.inputs_for>
</.form>

:warning: The following scenarios result in errors

  • Not setting as on inputs_for correctly → construction of binary failed: segment 1 of type 'binary': expected a binary but got: nil
  • Not setting default on inputs_for → inputs are not rendered correctly, only one shows up and it is empty.
  • Using List instead of Map for nested_field → errors were found at the given arguments: * 2nd argument: not a tuple