Step 5 - Implement the Legacy Storage Engine Converter¶
You can find all files used and modified in this step on GitHub.
So far, the Field Type's value is represented by the
It holds a semantic representation of the type's data: a URL, an author URL and the tweet's content.
The next step is to tell the system how to store it.
eZ Platform supports multiple storage engines. The main one 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, you need to map each Field Type value to something legacy can understand.
You will implement a Field Type Converter, each storage engine defining its own interface for those.
Legacy Field Type converters¶
The Legacy storage engine uses the
ezcontentobject_attribute table to store Field values,
ezcontentclass_attribute to store Field definition values (settings, etc.). They are both based on the same principle.
Each row represents a Field or a Field definition, and offers several free fields of different types, where the type can store its data:
ezcontentobject_attributeoffers three fields for this purpose:
ezcontentclass_attributeoffers a few more:
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 and configuration) and value.
The Converter will be placed alongside the Type and Value definitions (the kernel stores them inside the Legacy Storage Engine structure):
A Legacy Converter must implement the
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The Converter interface expects you to implement five methods:
toFieldValue()used to convert an API field value to a legacy storage value, and a legacy storage value to an API field value.
toFieldDefinition()used to convert a field definition to a legacy one, and a stored legacy field definition to an API field definition.
getIndexColumn()tells the API which legacy database field should be used to sort and filter content, either
Implementing Field Value converters: toFieldValue() and toStorageValue()¶
As said above, those two methods are used to convert from a Field to a value that Legacy can store, and the other way around.
You have defined that you wanted to store the tweet's URL in
data_text, and that sorting would be done on the
username-status-tweetid string you extract in
toStorageValue() will fill the provided
eZ\Publish\Core\Persistence\Legacy\Content\StorageFieldValue from a
toFieldValue() will do the opposite:
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With these two methods, the legacy storage engine is able to convert a
Tweet\Value into legacy data, and legacy data back into a
Implementing Field Definition converters:
The first two methods you have implemented apply to a Field's value, but you also need to convert the Field's definition.
For example, a TextLine's max length, or any
This is done using
toStorageDefinition() that converts a
FieldDefinition into a
toFieldDefinition() does the opposite. In this case, you actually don't need to implement those methods since the Tweet Type doesn't have settings:
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toStorageValue() you have used the
sortKeyString property from
getIndexColumn() will provide the legacy storage engine with the type of index / sort column it should use: string (
sort_key_string) or int (
Depending on which one is returned, the system will either use the
sortKeyString or the
sortKeyInt properties from the
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Registering the converter¶
Just like a Type, a Legacy Converter needs to be registered and tagged in the service container.
The tag is
ezpublish.storageEngine.legacy.converter, and it requires an
alias attribute to be set to the Field Type identifier (
Add this block to
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