Repeating Child Forms with InlineCRUD

Backpex.Fields.InlineCRUD renders repeated child forms. AshBackpex adds move-up and move-down controls alongside Backpex's add and delete controls, and supports the field as an opt-in for has_many relationships. The default Backpex.Fields.HasMany selection UI remains unchanged.

The demo uses InlineCRUD to edit an article's comments directly in the article form. Each comment has a body, author, sentiment, and approval status. The complete working modules are Demo.Blog.Post, Demo.Blog.Comment, and DemoWeb.PostLive.

Define the Relationship

The parent resource exposes a has_many relationship:

defmodule Demo.Blog.Post do
  use Ash.Resource,
    domain: Demo.Blog,
    data_layer: AshSqlite.DataLayer

  relationships do
    has_many :comments, Demo.Blog.Comment
  end
end

The child resource needs create, update, and destroy actions appropriate for the fields submitted by the repeated form. In the demo, body, sentiment, approved, and author_id are editable:

defmodule Demo.Blog.Comment do
  use Ash.Resource,
    domain: Demo.Blog,
    data_layer: AshSqlite.DataLayer

  attributes do
    uuid_primary_key :id

    attribute :body, :string do
      allow_nil? false
      public? true
    end

    attribute :sentiment, :atom do
      allow_nil? false
      default :neutral
      public? true
      constraints one_of: [:positive, :neutral, :critical]
    end

    attribute :approved, :boolean do
      allow_nil? false
      default false
      public? true
    end
  end

  relationships do
    belongs_to :post, Demo.Blog.Post do
      allow_nil? false
    end

    belongs_to :author, Demo.Blog.Author do
      allow_nil? false
    end
  end

  actions do
    defaults [:read, :destroy]

    create :create do
      primary? true
      accept [:body, :sentiment, :approved, :post_id, :author_id]
    end

    update :update do
      primary? true
      accept [:body, :sentiment, :approved, :post_id, :author_id]
    end
  end
end

Manage Comments in the Parent Actions

The parent create and update actions need an array-of-maps argument connected to the relationship with manage_relationship. The demo uses dedicated admin actions because its standard Post actions do not edit comments:

defmodule Demo.Blog.Post do
  use Ash.Resource,
    domain: Demo.Blog,
    data_layer: AshSqlite.DataLayer

  actions do
    create :admin_create do
      # Post attributes and other relationship arguments are omitted here.
      argument :comments, {:array, :map}, allow_nil?: true
      change manage_relationship(:comments, type: :direct_control)
    end

    update :admin_update do
      # Post attributes and other relationship arguments are omitted here.
      require_atomic? false
      argument :comments, {:array, :map}, allow_nil?: true
      change manage_relationship(:comments, type: :direct_control)
    end
  end
end

:direct_control creates new comments, updates comments whose primary keys are present, and destroys existing comments omitted from the submitted list.

Configure the LiveResource

Point the LiveResource at the actions above, load the relationship, then opt the relationship field into InlineCRUD:

defmodule DemoWeb.PostLive do
  use AshBackpex.LiveResource

  backpex do
    resource Demo.Blog.Post
    create_action :admin_create
    update_action :admin_update
    load [:author, :comments, :topic_tags, :audience_tags, :word_count, :comment_count]

    panels(
      content: "Content",
      publishing: "Publishing",
      relationships: "Relationships"
    )

    fields do
      field :comments do
        module Backpex.Fields.InlineCRUD
        except [:index]
        live_resource DemoWeb.CommentLive
        panel :relationships

        child_fields do
          field :body, Backpex.Fields.Textarea do
            label "Body"
            rows 3
            class "inline-crud-comment-body"
          end

          field :author, Backpex.Fields.BelongsTo do
            label "Author"
            display_field :name
            class "w-56"
          end

          field :sentiment, Backpex.Fields.Select do
            label "Sentiment"
            options Positive: :positive, Neutral: :neutral, Critical: :critical
            class "w-40"
          end

          field :approved, Backpex.Fields.Boolean do
            label "Approved"
            class "w-28"
          end
        end
      end
    end
  end
end

The demo gives the comment body its own row with two small CSS rules:

.flex:has(> .inline-crud-comment-body) {
  flex-wrap: wrap;
}

.inline-crud-comment-body {
  flex: 0 0 100%;
}

The child DSL accepts the same field options as top-level fields. This example uses a textarea, a relationship selector, a constrained select, and a boolean field. live_resource DemoWeb.CommentLive also lets Backpex link comments to their show pages in the read-only view.

For an Ash has_many relationship, AshBackpex supplies InlineCRUD's required type: :assoc option automatically. You can also set type :assoc explicitly.

Submitted Parameters

Backpex submits the repeated forms as an indexed map. It also provides:

• comments_order[], which contains the submitted child indexes in UI order.
• comments_delete[], which contains the indexes marked for deletion.
• comments_move_up[] or comments_move_down[], which contains the index selected by a move control.
• A hidden id inside each persisted comment form.
• A hidden _persistent_id that keeps each LiveView form row stable while it moves.

AshBackpex applies a requested move, removes deleted entries, and converts the remaining ordered entries into the list of maps expected by the Ash action. It retains each hidden primary key so manage_relationship can distinguish an update from a create.

The order controls preserve form order during submission. Persisting that order after reloading is still part of the child resource model; add a position attribute and set it from your child actions if the relationship needs durable ordering.

Limitations

Backpex does not support an InlineCRUD child field inside another InlineCRUD. Use InlineCRUD for one repeated relationship level and a custom field or dedicated editor for a nested repeater.