Embeds_many ids not submitted in params

Have you tried including a hidden input with the item ID inside inputs_for?

no, could you please show me a small example ? or point me to the docs for that ?

I noticed the following hidden input is being added by inputs_for

<input type="hidden" name="draft_order_creation_form[items][0][_persistent_id]" value="0">

But this is the changeset i’m turning into a form with to_form, why wouldn’t there be an id in the params ?

the form: %Phoenix.HTML.Form{
  source: #Ecto.Changeset<
    action: :validate,
    changes: %{
      items: [
        #Ecto.Changeset<
          action: :insert,
          changes: %{
            id: "01J3TDKVKQNFGMMM44FP0N8074",
            name: "400g / Einzeldose",
            image: "a",
            quantity: 1,
            price: Decimal.new("2.99"),
            variant_id: "01J3TDKVKQNFGMMM44FP0N8074"
          },
          errors: [],
          data: #Pdex.DraftOrderCreationForm.Item<>,
          valid?: true
        >
      ],
      shipping: #Ecto.Changeset<
        action: :insert,
        changes: %{method: "dpd"},
        errors: [price: {"can't be blank", [validation: :required]}],
        data: #Pdex.DraftOrders.Shipping<>,
        valid?: false
      >,
      discount: #Ecto.Changeset<
        action: :insert,
        changes: %{unit: :money},
        errors: [value: {"can't be blank", [validation: :required]}],
        data: #Pdex.DraftOrders.Discount<>,
        valid?: false
      >
    },
    errors: [
      customer_id: {"can't be blank", [validation: :required]},
      shipping_address_id: {"can't be blank", [validation: :required]},
      billing_address_id: {"can't be blank", [validation: :required]}
    ],
    data: #Pdex.DraftOrderCreationForm<>,
    valid?: false
  >,
  impl: Phoenix.HTML.FormData.Ecto.Changeset,
  id: "draft_order_creation_form",
  name: "draft_order_creation_form",
  data: %Pdex.DraftOrderCreationForm{
    order_id: nil,
    customer_id: nil,
    shipping_address_id: nil,
    billing_address_id: nil,
    note: nil,
    market_id: "01J3TCZA758GVB40QD7RWD6DTB",
    tags: [],
    discount: nil,
    shipping: nil,
    items: []
  },
  action: nil,
  hidden: [],
  params: %{
    "customer_id" => "",
    "customer_id_text_input" => "",
    "discount" => %{
      "_persistent_id" => "0",
      "reason" => "",
      "unit" => "money",
      "value" => ""
    },
    "items" => [
      %{
        "id" => "01J3TDKVKQNFGMMM44FP0N8074",
        "image" => "a",
        "name" => "400g / Einzeldose",
        "price" => "2.99",
        "product_name" => nil,
        "quantity" => 1,
        "variant_id" => "01J3TDKVKQNFGMMM44FP0N8074"
      }
    ],
    "items_text_input" => "",
    "market_id" => "01J3TCZA758GVB40QD7RWD6DTB",
    "note" => "",
    "shipping" => %{"_persistent_id" => "0", "method" => "dpd", "price" => ""},
    "tags_empty_selection" => "",
    "tags_text_input" => ""
  },
  errors: [
    customer_id: {"can't be blank", [validation: :required]},
    shipping_address_id: {"can't be blank", [validation: :required]},
    billing_address_id: {"can't be blank", [validation: :required]}
  ],
  options: [method: "post"],
  index: nil
}