Item provider strategy and item providers

On this page we describe what Item Provider Strategy and item providers are, list the main advantages of using item providers, and show a few examples of item providers in use.

Overview

The term Item Provider Strategy refers to an abstract logic of accessing data source items. In Magnolia 6 UI, the strategy is implemented in the form of item providers. The item providers cover one or more of the following two generic use cases:

• Item provider definition in a sub app descriptor, usually in the detail sub app. 
• Item provider definition In a form containing composite and complex fields.  In this use, the provider replaces the former field transformer functionality that is part of the UI framework 5, but no longer part of the Magnolia 6 UI.

Advantages of using item providers

Item Provider Strategy is a much simpler solution than the 5 UI field transformers. An item provider only needs to know how to access the data. In contrast, the transformers in the 5 UI framework were responsible for both types of data operations – reading and writing. In addition to this:

• The number of item providers is much lower in Magnolia 6 UI, compared to a relatively high number of field transformers in the 5 UI.
• The provider implementations can handle also JSON structures, task and notifications items, assets or a specific product content items.

The following item provider types are currently available:

• jcrNodeProvider - Base definition of JCR node provider strategies. It extends the ItemProviderDefinition.
• jcrNodeFromLocationProvider - Resolves node content from the current location. This provider extends the JcrNodeProviderDefinition.
• delegateToSubNodeProvider -  Returns the parent node. It extends the JcrNodeProviderDefinition. 
• fetchJcrSubNodeProvider -  Resolves child JCR node from the parent. It extends the JcrNodeProviderDefinition and is suitable for the sub forms only, since it relies on the parent.
• jsonProvider - Replaces the {id} path parameter with the one passed in the location and then fetches the result using a configured REST call. This provider type extends the ItemProviderDefinition.

In a sub app definition

In a sub app definition, a strategy is implemented for example in the Pages app, where the jcrNodeFromLocationProvider is used (see line 7 below). This provider type resolves a JCR node from location context:

  detail:
    class: info.magnolia.pages.app.detail.PageDetailDescriptor
    datasource:
      $type: jcrDatasource
      workspace: website
    itemProvider:
      $type: jcrNodeFromLocationProvider

(A snippet of an existing full definition, see https://git.magnolia-cms.com/projects/MODULES/repos/pages/browse/magnolia-pages-app/src/main/resources/pages-app/apps/pages-app.yaml.)

An item provider is not limited only to operations related to JCR content. See the following definition, where content items are provided from a JSON structure through the use of the jsonProvider (line 16):

  view:
    label: View Commit
    class: info.magnolia.ui.contentapp.detail.DetailDescriptor
    datasource:
      $type: jsonDatasource
      restClient: bitbucket
      restCall: commit
      jsonPathExpressions:
        properties:
          author: '$.author.raw'
    actions:
      cancel:
        label: Cancel
        $type: closeAction
    itemProvider:
      $type: jsonProvider

(A snippet of an existing full definition, see https://git.magnolia-cms.com/projects/MODULES/repos/rest-client/browse/declarative-rest-demo/apps/commits.yaml#50-65.)

In a form definition

A strategy can be used to handle data-read operations in forms containing complex field. Consider the following definition of a complex field called address, composed of two simple fields, city and country.

        address:
          label: address
          i18n: true
          $type: compositeField
          itemProvider:
            $type: fetchJcrSubNodeProvider
          properties:
            city:
              label: city
              $type: textField
            country:
              label: country
              i18n: true
              $type: textField

(A snippet of an existing full definition, see https://git.magnolia-cms.com/projects/MODULES/repos/contacts-app/browse/src/main/resources/contacts/apps/contacts-v8.yaml#320-336.)

Using the fetchJcrSubNodeProvider resolves the content of the child items city and country from the parent address: