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Item providers are a means for accessing items from data sources. On this page, we provide more details about their characteristics and main advantages, and we show a few examples of using them.

Overview

The concept of Item providers is an abstraction aiming to give developers a flexible way to specify which item a form field (simple or complex) should bind to and how an item should be accessed. 

Item providers allow you to bind form views to complex nested data structures and to fine tune such bindings. For example, if a form binds a contact address as a separate sub-form (a composite field in the Magnolia 5 UI context), the a Magnolia user might want to:

• Use a contact's child node to store the data, in which case an item provider that resolves a sub-node can be used.
• Store the properties directly on the contact node and keep it flat (. This would represent a self-reference item provider use case).

item Item providers get reference items as context. I.e. Applied to the contact address example, an address editor from the example upon data binding will get the root contact node so that it would be trivial to resolve the corresponding sub-node, if needed. Forms are always populated and persisted from top of the hierarchy to the bottom.

Typically, item providers are executed only:

• When fetching data from the back-end (to populate a form).
• When some Item providers kick in the form lifecycle only twice (typically): when the data is fetched from the backend (to populate the form) and when the updated data needs to be flushed from the Vaadin components back to the backend back-end (on a form commit).

Last but not least, item providers yield items wrapped into the Optional container, so it is fine not to return anything from the item provider implementation

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. In this case, however, the form data may not be populated or saved back to the

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back-end.

Main advantages

Item providers represent a much simpler solution than the field transformers in Magnolia 5 UI field transformers.

• Now, an 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 Magnolia 6 UI, data updates should be piped into the back-end items via simple fields by means of Vaadin 8 data binding (Binder objects).
• Unlike transformers, item providers do not have to deal with the deprecated Vaadin 7 Item API and do not require manual verifications that child properties are populated within an item.
• Item providers have a clearer concept of chaining. They get a reference of an item from a previous level in the hierarchy, making the whole complex data binding process recursive.
• The number of provider types is much lower in Magnolia 6 UI, compared to a relatively high number of field transformers in the 5 UI.
• There's also provider implementations that can handle JSON structures, task and notifications items, assets or specific product content items.

Where

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they can be used

Currently, item Item providers can be used in the following two use cases:

• Item provider definition in a detail subapp. 
• 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.

Provider types

The following item provider types are currently available:

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For any data source

form:
  properties:
    first_compositeField:
      $type: compositeField
      itemProvider:
        $type: currentItemProvider
      properties:
        inner_simple: # duplicate name
          $type: textField # first text
        inner_simple2:
          $type: textField # second text
    second_compositeField:
      $type: compositeField
      itemProvider:
        $type: currentItemProvider
      properties:
        inner_simple3:
          $type: textField # third text
        inner_simple: # duplicate name
          $type: textField # fourth text

# Problem with using currentItemProvider
edited_node:
  inner_simple: fourth text # first text is overwritten by second inner_simple
  inner_simple2: second text
  inner_simple3: third text

# Using jcrChildNodeProvider with both composite fields would fix the problem
edited_node:
  first_compositeField:
    inner_simple: first text
    inner_simple2: second text
  second_compositeField:
    inner_simple3: third text
    inner_simple: fourth text # no name conflict

For JCR data source

For JSON data source

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The jcrGetCurrentNodeProvider and jcrGetChildNodeProvider are suitable for sub forms only since a dependency on a parent node is presupposed to exist.

Used in a sub app definition

In subapp definition

The jcrNodeFromLocationProvider is used 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 its location context:

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(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 Using item provider providers 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 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.)

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In form definition

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

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

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