Nested in Forms

You can use "Show on edit screens" to make the field available in the edit view. However, this will render it using the show view component.

To enable nested creation for the field, allowing it to be created and / or edited alongside its parent record within the same form, use the nested option which is a hash with configurable option.

The avo-nested gem

Nested association forms are provided by the avo-nested gem. Add it to your Gemfile using the same private gem source as your other Avo paid gems:

gem "avo-nested", source: "https://packager.dev/avo-hq/"

Run bundle install. If you have not set up packager.dev access yet, see Gem server authentication.

Keep in mind that this will display the field’s resource as it appears in the edit view.

-> nested

Enables this field as a nested form in the specified views.

Default value

{}

Possible values

A hash with the following options:

• on: Views in which to enable nesting. Accepted values:
  • :new - Enables nesting in the new view.
  • :edit - Enables nesting in the edit view.
  • :forms - Enables nesting in the new and edit views.
• limit: (Only for has_many and has_and_belongs_to_many fields) Hides the "Add" button when the specified limit is reached.

TIP

Setting nested: true is a shortcut for nested: { on: :forms }.

Deleting existing records

Since avo-nested >= v4.3.3

A record added in the form but not saved yet can be removed at any time. An existing record gets a "Delete" button only when the parent model opts in with allow_destroy: true:

# app/models/book.rb
accepts_nested_attributes_for :authors, allow_destroy: true

Clicking it asks for confirmation, then marks the record for deletion. It stays in the form, dimmed, with an "Undo" link, and nothing happens until the parent form is saved. Saving destroys the record. See Authorization for the policy check that applies.

Example

# app/avo/resources/book.rb
class Avo::Resources::Book < Avo::BaseResource
  def fields
    # Shortcut for full nesting
    field :authors, as: :, nested: true

    # Explicit nesting on new only
    field :authors, as: :, nested: { on: :new }

    # Explicit nesting on edit only
    field :authors, as: :, nested: { on: :edit }

    # Explicit nesting on both new and edit
    field :authors, as: :, nested: { on: :forms }

    # Limit nested creation (for has_many or has_and_belongs_to_many only)
    field :authors,
      as: :,
      nested: { on: [:new, :edit], limit: 2 }
  end
end

Authorization

With authorization enabled, a nested form writes a child only when the child's own pages would let the user write it.

• Existing records are saved only when they are inside the child resource's policy scope and the child policy allows update?. update? is asked twice: once with the record as loaded, and again with the submitted values. A row the user may not update is skipped, and the rest of the form still saves.
• Records marked for deletion are destroyed only when they are inside the policy scope and the child policy allows destroy?. If destroy? refuses, the save is refused.
• New records need the child policy's create? and the parent policy's create_authors?. If either refuses, the save is refused.
• When create_authors? refuses, the form hides its "Add" button, the same way the association panel hides "Create new".

INFO

With explicit_authorization on, a parent policy that doesn't define create_authors? refuses new rows. Define it to let users add records from the form:

# app/policies/book_policy.rb
class BookPolicy < ApplicationPolicy
  def create_authors?
    user.admin?
  end
end