Transforming field values

The value of a form field is typically stored in a single property in the repository. A text field named firstName stores its value in a property firstName. Use a property transformer to read and write values in a different way.

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 override the default. Add the transformerClass property into your field definition and set its value to a fully-qualified class name.

Default transformer classes:

• For simple fields such as Text and Date: info.magnolia.ui.form.field.transformer.basic.BasicTransformer
• For composite fields: info.magnolia.ui.form.field.transformer.composite.CompositeTransformer

• For switchable fields: info.magnolia.ui.form.field.transformer.composite.SwitchableTransformer

• For multivalue field: info.magnolia.ui.form.field.transformer.multi.MultiValueTransformer 

Other available transformer classes:

• info.magnolia.ui.form.field.transformer.composite.DelegatingCompositeFieldTransformer Magnolia 5.2.5+
• info.magnolia.ui.form.field.transformer.multi.DelegatingMultiValueFieldTransformer Magnolia 5.2.5+
• info.magnolia.ui.form.field.transformer.composite.NoOpCompositeTransformer
• info.magnolia.ui.form.field.transformer.multi.MultiValueJSONTransformer
• info.magnolia.ui.form.field.transformer.multi.MultiValueChildrenNodeTransformer
• info.magnolia.ui.form.field.transformer.multi.MultiValueChildNodeTransformer
• info.magnolia.ui.form.field.transformer.multi.MultiValueSubChildrenNodeTransformer
  
  

BasicTransformer

The 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 exist yet.

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

Here is an example dialog with some 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 in the field definition.

Here is an example field definition where type is set to Date. Magnolia will store the field value as a date object.

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

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

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

Here is a composite event field. It consists of a text field and a date field.

The CompositeTransformer stores the values like this:

DelegatingCompositeFieldTransformer

The 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 storage property name.

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

Here is a composite field event that contains a title field and a date field.

The field is defined using a DelegatingCompositeFieldTransformer:

A normal CompositeTransformer would store values like this:

The 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 the  NoOpCompositeTransformer  for a composite field that is inside a multivalue parent field. "NoOp" means no operation – the 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 a 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 plainText and richText fields.

The 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 to the start of 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 the 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 LinkedList 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.

The 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.

The 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:

The 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.

MultiValueChildrenNodeTransformer

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

The 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.

The 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.

The 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.

The MultiValueSubChildrenNodeTransformer stores values like this:

MultiValueSubChildrenNodePropertiesTransformer

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

This transformer 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.

The 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 the DelegatingMultiValueTransformer and the DelegatingCompositeFieldTransformer.

Here's how transforming values is 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: