Stores value for $field in an external data source.
The whole {@link eZ\Publish\SPI\Persistence\Content\Field} object is passed and its value
is accessible through the {@link eZ\Publish\SPI\Persistence\Content\FieldValue} 'value' property.
This value holds the data filled by the user as a {@link eZ\Publish\Core\FieldType\Value} based object,
according to the field type (e.g. for TextLine, it will be a {@link eZ\Publish\Core\FieldType\TextLine\Value} object).
$field->id = unique ID from the attribute tables (needs to be generated by
database back end on create, before the external data source may be
called from storing).
The context array provides some context for the field handler about the
currently used storage engine.
The array should at least define 2 keys :
- identifier (connection identifier)
- connection (the connection handler)
For example, using Legacy storage engine, $context will be:
- identifier = 'LegacyStorage'
- connection = {@link \eZ\Publish\Core\Persistence\Database\DatabaseHandler} object handler (for DB connection),
to be used accordingly to
The context array provides some context for the field handler about the
currently used storage engine.
The array should at least define 2 keys :
- identifier (connection identifier)
- connection (the connection handler)
For example, using Legacy storage engine, $context will be:
- identifier = 'LegacyStorage'
- connection = {@link \eZ\Publish\Core\Persistence\Database\DatabaseHandler} object handler (for DB connection),
to be used accordingly to
{@link http://incubator.apache.org/zetacomponents/documentation/trunk/Database/tutorial.html ezcDatabase} usage
This method might return true if $field needs to be updated after storage done here (to store a PK for instance).
In any other case, this method must not return anything (null).
