Transforming field values

The value of a form field is typically stored in a single property. For example, text field firstName stores its value in a property firstName. This page explains how to read and write values in different ways using property transformers.

Property transformer is a layer that translates the stored values into something the user can edit and vice versa. This is useful for complex fields such as multivalue and composite where more than one property is needed to store the entire field value. The transformer stands between the form and the JCR Item  representation, which means that individual form fields are not directly accessed by the Item.

Transformer classes

Property transformer classes define how field values are stored in the repository. Each field has a default transformer class. You don't need to define a class unless you want to change the default. To change the class, add a transformerClass property to your field definition and set its value to a fully-qualified transformer class name.

BasicTransformer

BasicTransformer stores the field value in a single property. The property has the same name as the field definition node. You can provide a different name with a name property in the field definition. This transformer creates a new property if the property does not yet exist.

Transformer class: info.magnolia.ui.form.field.transformer.basic.BasicTransformer

Here is an example dialog with text  fields:

The BasicTransformer stores the field values like this in the JCR repository:

Setting a property type

All JCR properties have a type. The basic transformer uses the String type for all properties by default. You can use a different type by adding a type property to the field definition .

Example field definition with type is set to Date. Magnolia will store the field value as a date object.

form:
  tabs:
    - name: tabText
      label: Text
      fields:
        - name: title
          fieldType: text
          label: Event
          type: Date

If you define a defaultValue, that value will be converted to the desired type too. If you don't define a default value, the property will have a null start value.

i18n support

If a field supports translation, an i18n language suffix is added to the property name.

For example, a simpleText field that supports translation has suffixes en, de and fr. In this example, English is the default (fallback) language so the en suffix is not used.

Composite transformers

CompositeTransformer

CompositeTransformer stores each child field value as a single property. Composite fields which consist of multiple child fields use CompositeTransformer by default.

Transformer class: info.magnolia.ui.form.field.transformer.composite.CompositeTransformer  

This composite event field consists of a text field and a date field.

CompositeTransformer stores the values like this:

DelegatingCompositeFieldTransformer

DelegatingCompositeFieldTransformer stores each child field value as a single property. The difference between this transformer and the other composite transformers is that it uses the child field name as the storage property name.

Transformer class:info.magnolia.ui.form.field.transformer.composite.DelegatingCompositeFieldTransformer

Example composite field definition containing a text field and date field that uses DelegatingCompositeFieldTransformer  :

form:
  tabs:
    - name: tabEvent
      label: Event
      fields:
        - name: composite
          fieldType: composite
          transformerClass:  info.magnolia.ui.form.field.transformer.composite.DelegatingCompositeFieldTransformer
          label: Event
          fields:
            - name: title
              fieldType: text
              label: Title
            - name: date
              fieldType: date
              label: Date

CompositeTransformer would store values like this:

DelegatingCompositeFieldTransformer stores values like this:

When i18n=true this transformer delegates localization to the child fields.  Add the i18n=true property in the parent field AND in any child fields. The property needs to be added to both levels.

NoOpCompositeTransformer

Use NoOpCompositeTransformer for a  composite field that is inside a  multivalue parent field. "NoOp" means no operation – NoOpCompositeTransformer  does not perform any  writeToItem  or  readFromItem  operations, it just acts as a property container. The transformer of the parent multivalue field does the reading and writing of the item structure to the repository. You can use any of the multivalue transformers below in the parent. The parent transformer passes the properties to the  NoOpCompositeTransformer  as a Vaadin  PropertysetItem  .

Transformer class: info.magnolia.ui.form.field.transformer.composite.NoOpCompositeTransformer

SwitchableTransformer

Switchable fields use SwitchableTransformer by default. This transformer stores the selected field value as a single suffixed property.

Transformer class: info.magnolia.ui.form.field.transformer.composite.SwitchableTransformer

Here is a switchable text editor field. It consists of alternative text and rich text fields.

SwitchableTransformer stores the values like this. The parent option field has one property (editor) and each child field has its own property (editorplainText, editorrichText). The name of the parent field is appended before the child property name.

Multivalue transformers

Use multivalue transformers with multivalue fields. They are capable of storing multiple values, even in cases where the multivalue parent field contains a composite field.

 Use DelegatingMultiValueTransformer when nesting more than two levels of fields. The other multivalue transformers can handle only two levels.

MultiValueTransformer

MultiValueTransformer is the default transformer for  multivalue  fields. The transformer stores field values in a LinkedList<T> collection. The linked list is then automatically converted to a JCR multivalue property when persisted to the JCR.  In the repository it looks like a typical array: comma-separated and enclosed in square brackets.

 Use this transformer only when the multivalue parent contains a single field such as text, date and checkbox.

Transformer class: info.magnolia.ui.form.field.transformer.multi.MultiValueTransformer

Here is a  multivalue field that consists of a  text  field.

MultiValueTransformer stores the values as a JCR multivalue property that looks like a typical array.

MultiValueJSONTransformer

MultiValueJSONTransformer stores the values as a comma-separated list of Strings.

 Use this transformer only for simple fields such as text, date and checkbox.

Transformer class: info.magnolia.ui.form.field.transformer.multi.MultiValueJSONTransformer

Here is a  multivalue field that consists of a  text field.

MultiValueJSONTransformer stores the values like this:

DelegatingMultiValueTransformer

DelegatingMultiValueFieldTransformer delegates the responsibility of storing field values to the parent field. In doing so, this transformer creates a list of Item objects. The child field uses the Item to create and retrieve its own properties. Delegation makes it possible to nest unlimited levels of fields. For example, create a composite field which contains a multivalue field which contains a switchable field and so on.

 Use DelegatingMultiValueTransformer when nesting more than two levels of fields. The other multivalue transformers can only handle two levels max.

Transformer class: info.magnolia.ui.form.field.transformer.multi.DelegatingMultiValueFieldTransformer

Here is a  multivalue field that consists of a  text field.

This is how the nested fields are defined when using DelegatingMultiValueTransformer:

form:
  tabs:
    - name: tabMain
      label: Main
      fields:
        - name: shoppingList
          fieldType: multiValue
          label: Shopping list
          transformerClass: info.magnolia.ui.form.field.transformer.multi.DelegatingMultiValueFieldTransformer
          field:
            fieldType: text
            name: shoppingitem

DelegatingMultiValueFieldTransformer stores the values like this:

When i18n=true this transformer creates nodes with a locale suffix. The translated values are stored in properties under the nodes.  Add the i18n=true property in the parent field AND in any child fields. The property needs to be added to both levels.

DelegatingMultiValueSubnodeTransformer

DelegatingMultiValueSubnodeTransformer is a variant to the DelegatingMultiValueFieldTransformer but with child values consisting of sub nodes.

Transformer class: info.magnolia.ui.form.field.transformer.multi.DelegatingMultiValueSubnodeTransformer

Here is a  multivalue field that consists of composite  text fields.

This is how the fields are defined when using DelegatingMultiValueSubnodeTransformer:

form:
  tabs:
    - name: tabMain
      label: Main
      fields:
        - name: shoppingList
          label: Shopping list
          fieldType: multiValue
          transformerClass: info.magnolia.ui.form.field.transformer.multi.DelegatingMultiValueSubnodeTransformer
          field:
            fieldType: composite
            transformerClass: info.magnolia.ui.form.field.transformer.composite.DelegatingCompositeFieldTransformer
            fields:
              - name: item1
                label: Item 1
                fieldType: text
              - name: item2
                label: Item 2
                fieldType: text

DelegatingMultiValueSubnodeTransformer stores the values like this:

Storage after enabling i18n=true for each of the fields and the parent:

MultiValueChildrenNodeTransformer

Use the more versatile DelegatingMultiValueTransformer instead of this transformer if you can.

MultiValueChildrenNodeTransformer

MultiValueChildrenNodeTransformer doesn't create a node for the multivalue parent field at all. It creates nodes for the child fields and stores their values as properties. This structure is equivalent to the JCR structure of the form Item.

Transformer class: info.magnolia.ui.form.field.transformer.multi.MultiValueChildrenNodeTransformer

Here is a  multivalue field that consists of a  text field.

MultiValueChildrenNodeTransformer stores the values like this:

MultiValueSubChildNodeTransformer

Use the more versatile DelegatingMultiValueTransformer instead of this transformer if you can.

MultiValueSubChildrenNodeTransformer first creates a node for the parent multivalue field. It then stores the child fields as numbered properties.

Transformer class: info.magnolia.ui.form.field.transformer.multi.MultiValueChildNodeTransformer

Here is a  multivalue field that consists of a  text field.

MultiValueSubChildNodeTransformer stores values like this:

MultiValueSubChildrenNodeTransformer

Use the more versatile DelegatingMultiValueTransformer instead of this transformer if you can.

MultiValueSubChildrenNodeTransformer first creates a node for the parent multivalue field. It then stores the child fields as subnodes and their values as properties.

Transformer class: info.magnolia.ui.form.field.transformer.multi.MultiValueSubChildrenNodeTransformer

Here is a  multivalue field that consists of a  text field.

MultiValueSubChildrenNodeTransformer stores values like this:

MultiValueSubChildrenNodePropertiesTransformer

Use the more versatile DelegatingMultiValueTransformer instead of this transformer if you can.

MultiValueSubChildrenNodePropertiesTransformer is equivalent to MultiValueChildrenNodeTransformer but it is able to handle a composite field as the child of the multivalue parent.

Transformer class: info.magnolia.ui.form.field.transformer.multi.MultiValueSubChildrenNodePropertiesTransformer

Define a no-op transformer for the composite child field. Since the parent multivalue field handles the read and write operations, set the composite field's transformerClass to info.magnolia.ui.form.field.transformer.composite.NoOpCompositeTransformer.

Here is a multivalue event field. Each event is a composite field that consists of a title and a date.

MultiValueSubChildrenNodePropertiesTransformer stores each composite field as an item (node) and the values of the child fields as properties. 

Which transformer should I use?

• I have a multi-value field with a simple field inside (e.g. text, single-select, date, link): all multi-value transformers may be used.
• I have a multi-value field with a complex field inside (e.g. composite, switchable, multi-selection, or any other field with a custom transformerClass): only delegating transformers should be used (same goes for nested composite & switchable fields).

Combining delegating transformers

In this complex example we nest four levels of fields. To book a seat on a flight you enter a departure city, arrival city and select one or more seats depending on the number of passengers.

We need to use delegating field transformers since normal non-delegating transformers can only handle two nesting levels. Also, since we mix multivalue and composite fields we need to use both DelegatingMultiValueTransformer and the DelegatingCompositeFieldTransformer.

Here's how transforming values are delegated:

1. DelegatingMultiValueTransformer on multivalue field flights creates a new Item and passes it to composite field flight.
2. The Item is passed to the composite child fields from, to and seats, in order to initialize their own properties and Items.
3. Text fields from and to add their text properties to the Item.
4. Nested composite field seats uses the Item to create a subitem and sends the subitem to its child field seat.

The values are stored in the JCR repository like this: