Context Assigns

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Callbacks that are called while the index and show views are rendered receive the assigns of the LiveView, for example Backpex.LiveResource.can?/3, Backpex.LiveResource.index_row_class/4, the callbacks of item actions, the render/1 and render_form/1 callbacks of filters, and the functions and callbacks of fields.

By default, Backpex passes all assigns. LiveView cannot know which of them these callbacks actually use, so it re-renders the table with every field component, the filters, the action buttons and the fields of the show view whenever any assign of the LiveView changes, even one that is only used somewhere else, like the visibility of the metrics or an assign of your own render_resource_slot/3.

Configure LiveResource

Set the context_assigns option to the assigns your callbacks need in addition to the ones Backpex always passes (:live_resource, :live_action, :params, :fields, :item_actions, :return_to, the :item of the show view, which is nil on the index view or the base_schema of a resource action while one is open, and a :socket for building routes; the functions and callbacks of fields on the index view receive the item of their row as :item instead):

# in your LiveResource module
defmodule MyAppWeb.Live.UserLive do
  use Backpex.LiveResource,
    ...,
    context_assigns: [:current_scope]
end

These parts are then only re-rendered when their data or one of these assigns changes.

Warning

These callbacks no longer see any other assign. Add every assign that your can?/3, index_row_class/4, item actions, filters and fields read to context_assigns. The :socket only carries the router and endpoint, so use :all if your callbacks need anything else from it.

Backpex.LiveResource.filters/1 and the can?/1 callback of filters always receive all assigns. The index view evaluates them on every render. Functions that do not run while rendering also receive all assigns, for example the item_query of the adapter config, the queries of filters and saving an inline edit of an index_editable field. The changeset and Backpex.LiveResource.can?/3 of an inline edit receive the same assigns as in the edit form, and Backpex.LiveResource.on_item_updated/2 receives the socket of the LiveView. Custom fields that save their inline edits with Backpex.Field.handle_index_editable/3 instead of rendering Backpex.HTML.Form.index_form/1 only receive the listed assigns, see the Index Edit guide.