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eZ Publish (5.x)

eZ Publish 5.x | For eZ Platform & eZ Studio topics see Technical manual and User manual, for eZ Publish 4.x and Legacy topics see eZ Publish legacy

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So far, our type’s value is represented by the Tweet\Value class. It holds a semantic representation of the type’s data: an url, and author url, and the tweet's content.

The next step is to tell the system how to actually store this.

About converters

Unlike eZ Publish Legacy, eZ Publish 5 supports (by design) multiple storage engines. The main, and almost only one right now is the Legacy Storage Engine, based on the legacy database, with a new implementation. Since each storage engine may have its own way of storing data, we need to map each FieldType value to something legacy can understand. To do this, we will implement a FieldType Converter, each storage engine defining its own interface for those.

Legacy FieldType converters

The legacy storage engine uses the ezcontentobject_attribute table to store field values, and ezcontentclass_attribute to store field definition values (settings, etc). They're both based on the same principle. Each row reprensents a Field or a FieldDefinition, and offers several free fields, of different types, where the type can store its data:

...

Each type is free to use those fields in any way it requires. Converters will map a field’s semantic values to the fields described above, for both settings (validation + configuration) as well as value.

Implementing Tweet\LegacyConverter

The Converter will be placed along with the Type and Value definitions (the Kernel stores them inside the Legacy Storage Engine structure): eZ/Publish/FieldType/Tweet/LegacyConverter.php. A Legacy Converter must implement the eZ\Publish\Core\Persistence\Legacy\Content\FieldValue\Converter interface:

...

  • toStorageValue() & toFieldValue()
    used to convert an API field value to a legacy storage value, and a legacy storage value to an API field value. 

  • toStorageFieldDefinition() & toFieldDefinition()
    used to convert a field definition to a legacy one, and a stored legacy field definition to an API field definition 

  • getIndexColumn()
    Tell the API which legacy DB field should be used to sort & filter content, either sort_key_string or sort_key_int

Implementing Field Value converters: toFieldValue() and toStorageValue()

As said above, those two methods are used to convert from a Field to a value Legacy can store, and the other way around.

...

With these two methods, the legacy storage engine is able to convert a Tweet\Value into legacy data, and legacy data back into a Tweet\Value object.

Implementing Field Definition converters: toStorageFieldDefinition() and toFieldDefinition()

The first two methods we have implemented apply to a Field’s value. But we also need to convert our Field’s definition. For example, a TextLine’s max length, or any FieldDefinition option.

...

Code Block
use eZ\Publish\Core\Persistence\Legacy\Content\StorageFieldDefinition;
use eZ\Publish\SPI\Persistence\Content\Type\FieldDefinition;

// [...]

public function toStorageFieldDefinition( FieldDefinition $fieldDef, StorageFieldDefinition $storageDef )
{
}
 
public function toFieldDefinition( StorageFieldDefinition $storageDef, FieldDefinition $fieldDef )
{
}

Implementing getIndexColumn()

In toFieldValue() and toStorageValue(), we have used the sortKeyString property from StorageFieldValue. getIndexColumn() will tell provide the legacy storage engine the type of index / sort column it should use: string (sort_key_string) or int (sort_key_int). Depending on which one is returned, the system will either use the sortKeyString or the sortKeyInt properties from the StorageFieldValue.

...