The schema is lazy-loaded by the first call to Model::schema(), unless it has been manually defined in the Model subclass.

For schemaless persistent storage (e.g. MongoDB), this is never populated automatically - if you desire a fixed schema to interact with in those cases, you will be required to define it yourself.

Example:

protected $_schema = array(
    '_id'  => array('type' => 'id'), // required for Mongo
    'name' => array('type' => 'string', 'default' => 'Moe', 'null' => false),
    'sign' => array('type' => 'string', 'default' => 'bar', 'null' => false),
    'age'  => array('type' => 'integer', 'default' => 0, 'null' => false)
);

For MongoDB specifically, you can also implement a callback in your database connection configuration that fetches and returns the schema data, as in the following:

// config/bootstrap/connections.php:
Connections::add('default', array(
 'type' => 'MongoDb',
 'host' => 'localhost',
 'database' => 'app_name',
 'schema' => function($db, $collection, $meta) {
     $result = $db->connection->schemas->findOne(compact('collection'));
     return $result ? $result['data'] : array();
 }
));

This example defines an optional MongoDB convention in which the schema for each individual collection is stored in a "schemas" collection, where each document contains the name of a collection, along with a 'data' key, which contains the schema for that collection, in the format specified above.

When defining '$_schema' where the data source is MongoDB, the types map to database types as follows:

 id      => MongoId
 date    => MongoDate
 regex   => MongoRegex
 integer => integer
 float   => float
 boolean => boolean
 code    => MongoCode
 binary  => MongoBinData