lithium\data\Model

class

The Model class is the starting point for the domain logic of your application. Models are tasked with providing meaning to otherwise raw and unprocessed data (e.g. user profile).

Models expose a consistent and unified API to interact with an underlying data source (e.g. MongoDB, CouchDB, MySQL) for operations such as querying, saving, updating and deleting data from the persistent storage.

Classes extending this one should, conventionally, be named as Plural, CamelCase and be placed in the models directory. i.e. a posts model would be model/Posts.php.

Models allow you to interact with your data in two fundamentally different ways: querying, and data mutation (saving/updating/deleting). All query-related operations may be done through the static find() method, along with some additional utility methods provided for convenience.

Examples:

// Return all 'post' records
Posts::find('all');
Posts::all(); // This is equivalent to the above.

// With conditions and a limit
Posts::find('all', ['conditions' => ['published' => true], 'limit' => 10]);

// Integer count of all 'post' records
Posts::find('count');

// With conditions
Posts::find('count', ['conditions' => ['published' => true]]);

The actual objects returned from find() calls will depend on the type of data source in use. MongoDB, for example, will return results as a Document (as will CouchDB), while MySQL will return results as a RecordSet. Both of these classes extend a common lithium\data\Collection class, and provide the necessary abstraction to make working with either type completely transparent.

For data mutation (saving/updating/deleting), the Model class acts as a broker to the proper objects. When creating a new record or document, for example, a call to Posts::create() will return an instance of lithium\data\entity\Record or lithium\data\entity\Document, which can then be acted upon.

Example:

$post = Posts::create();
$post->author = 'Robert';
$post->title = 'Newest Post!';
$post->content = 'Lithium rocks. That is all.';

$post->save();

Source

class Model extends \lithium\core\StaticObject {

	use \lithium\core\MergeInheritable;

	/**
	 * Criteria for data validation.
	 *
	 * Example usage:
	 * ```
	 * public $validates = [
	 *     'title' => 'please enter a title',
	 *     'email' => [
	 *         ['notEmpty', 'message' => 'Email is empty.'],
	 *         ['email', 'message' => 'Email is not valid.'],
	 *     ]
	 * ];
	 * ```
	 *
	 * @var array
	 */
	public $validates = [];

	/**
	 * Model hasOne relations.
	 *
	 * @var array
	 */
	public $hasOne = [];

	/**
	 * Model hasMany relations.
	 *
	 * @var array
	 */
	public $hasMany = [];

	/**
	 * Model belongsTo relations.
	 *
	 * @var array
	 */
	public $belongsTo = [];

	/**
	 * Stores model instances for internal use.
	 *
	 * While the `Model` public API does not require instantiation thanks to late static binding
	 * introduced in PHP 5.3, LSB does not apply to class attributes. In order to prevent you
	 * from needing to redeclare every single `Model` class attribute in subclasses, instances of
	 * the models are stored and used internally.
	 *
	 * @var array
	 */
	protected static $_instances = [];

	/**
	 * List of initialized instances.
	 *
	 * @see lithium\data\Model::_initialize();
	 * @var array
	 */
	protected static $_initialized = [];

	/**
	 * Class dependencies.
	 *
	 * @var array
	 */
	protected $_classes = [
		'connections' => 'lithium\data\Connections'
	];

	/**
	 * A list of the current relation types for this `Model`.
	 *
	 * @var array
	 */
	protected $_relations = [];

	/**
	 * Matching between relation's fieldnames and their corresponding relation name.
	 *
	 * @var array
	 */
	protected $_relationFieldNames = [];

	/**
	 * List of relation types.
	 *
	 * Valid relation types are:
	 * - `belongsTo`
	 * - `hasOne`
	 * - `hasMany`
	 *
	 * @var array
	 */
	protected $_relationTypes = ['belongsTo', 'hasOne', 'hasMany'];

	/**
	 * Store available relation names for this model which still unloaded.
	 *
	 * @var array This array use the following notation : `relation_name => relation_type`.
	 */
	protected $_relationsToLoad = [];

	/**
	 * Specifies all meta-information for this model class, including the name of the data source it
	 * connects to, how it interacts with that class, and how its data structure is defined.
	 *
	 * - `connection`: The name of the connection (as defined in `Connections::add()`) to which the
	 *   model should bind
	 * - `key`: The primary key or identifier key for records / documents this model produces,
	 *   i.e. `'id'` or `array('_id', '_rev')`. Defaults to `'id'`.
	 * - `name`: The canonical name of this model. Defaults to the class name.
	 * - `source`: The name of the database table or document collection to bind to. Defaults to the
	 *   lower-cased and underscored name of the class, i.e. `class UserProfile` maps to
	 *   `'user_profiles'`.
	 * - `title`: The field or key used as the title for each record. Defaults to `'title'` or
	 *   `'name'`, if those fields are available.
	 *
	 * @var array
	 * @see lithium\data\Connections::add()
	 */
	protected $_meta = [
		'name' => null,
		'title' => null,
		'class' => null,
		'source' => null,
		'connection' => 'default'
	];

	/**
	 * Array of closures used to lazily initialize metadata.
	 *
	 * @var array
	 */
	protected $_initializers = [];

	/**
	 * Defines the data schema in array notation or, after initialization, holds the
	 * schema object.
	 *
	 * `Model` subclasses can manually define a schema in array notation. The array
	 * notation will then be lazily converted to a schema object by the first call to
	 * `Model::schema()`.
	 *
	 * The schema should only be defined in subclasses for schemaless persistent data
	 * sources (e.g. MongoDB), for all other data sources this is done automatically. If
	 * you desire a fixed schema for a schemaless data source, the following example shows
	 * how you'd define one manually.
	 *
	 * For MongoDB specifically, you can also automate schema definition. Please see
	 * lithium\data\soure\MondoDb::$_schema for more information.
	 *
	 * ```
	 * protected $_schema = [
	 *     '_id'  => ['type' => 'id'],
	 *     'name' => ['type' => 'string', 'default' => 'Moe', 'null' => false],
	 *     'sign' => ['type' => 'string', 'default' => 'bar', 'null' => false],
	 *     'age'  => ['type' => 'integer', 'default' => 0, 'null' => false]
	 * ];
	 * ```
	 *
	 * @see lithium\data\source\MongoDb::$_schema
	 * @see lithium\data\Model::schema()
	 * @see lithium\data\Schema
	 * @var array|\lithium\data\Schema
	 */
	protected $_schema = [];

	/**
	 * Default query parameters for the model finders.
	 *
	 * Can be either redefined in a model subclass or changed during runtime
	 * using `Model::query()`.
	 *
	 * For a detailed description of the available query options below see
	 * the description of the `$options` parameter of `Model::find()`.
	 *
	 * @see lithium\data\Model::find()
	 * @see lithium\data\Model::query()
	 * @see lithium\data\model\Query::__construct()
	 * @var array
	 */
	protected $_query = [
		'fields'     => null,
		'conditions' => null,
		'having'     => null,
		'group'      => null,
		'order'      => null,
		'limit'      => null,
		'offset'     => null,
		'page'       => null,
		'with'       => [],
		'joins'      => []
	];

	/**
	 * Custom find query properties, indexed by name.
	 *
	 * @see lithium\data\Model::finder()
	 * @var array
	 */
	protected $_finders = [];

	/**
	 * Stores all custom instance methods created by `Model::instanceMethods`.
	 *
	 * @var array
	 */
	protected static $_instanceMethods = [];

	/**
	 * Holds an array of values that should be processed on `Model::config()`. Each value should
	 * have a matching protected property (prefixed with `_`) defined in the class. If the
	 * property is an array, the property name should be the key and the value should be `'merge'`.
	 *
	 * @see lithium\data\Model::config()
	 * @var array
	 */
	protected $_autoConfig = [
		'meta',
		'finders',
		'query',
		'schema',
		'classes',
		'initializers'
	];

	/**
	 * Holds an array of attributes to be inherited.
	 *
	 * @see lithium\data\Model::_initialize()
	 * @var array
	 */
	protected $_inherits = [];

	/**
	 * Configures the model for use. This method will set the `Model::$_schema`, `Model::$_meta`,
	 * `Model::$_finders` class attributes, as well as obtain a handle to the configured
	 * persistent storage connection.
	 *
	 * @param array $config Possible options are:
	 *        - `meta`: Meta-information for this model, such as the connection.
	 *        - `finders`: Custom finders for this model.
	 *        - `query`: Default query parameters.
	 *        - `schema`: A `Schema` instance for this model.
	 *        - `classes`: Classes used by this model.
	 */
	public static function config(array $config = []) {
		if (($class = get_called_class()) === __CLASS__) {
			return;
		}

		if (!isset(static::$_instances[$class])) {
			static::$_instances[$class] = new $class();
		}
		$self = static::$_instances[$class];

		foreach ($self->_autoConfig as $key) {
			if (isset($config[$key])) {
				$_key = "_{$key}";
				$val = $config[$key];
				$self->$_key = is_array($val) ? $val + $self->$_key : $val;
			}
		}

		static::$_initialized[$class] = false;
	}

	/**
	 * Init default connection options and connects default finders.
	 *
	 * This method will set the `Model::$_schema`, `Model::$_meta`, `Model::$_finders` class
	 * attributes, as well as obtain a handle to the configured persistent storage connection
	 *
	 * @param string $class The fully-namespaced class name to initialize.
	 * @return object Returns the initialized model instance.
	 */
	protected static function _initialize($class) {
		$self = static::$_instances[$class];

		if (isset(static::$_initialized[$class]) && static::$_initialized[$class]) {
			return $self;
		}
		static::$_initialized[$class] = true;

		$properties = [
			'validates',
			'belongsTo',
			'hasMany',
			'hasOne',
			'_meta',
			'_finders',
			'_query',
			'_classes',
			'_initializers'
		];
		if (is_array($self->_schema)) {
			$properties[] = '_schema';
		}
		if ($self->_inherits) {
			$properties = array_merge($self->_inherits, $properties);
		}
		$self->_inherit($properties);

		$source = [
			'classes' => [], 'meta' => [], 'finders' => [], 'schema' => []
		];

		$meta = $self->_meta;
		if ($meta['connection']) {
			$classes = $self->_classes;
			$conn = $classes['connections']::get($meta['connection']);
			$source = (($conn) ? $conn->configureClass($class) : []) + $source;
		}

		$self->_classes += $source['classes'];
		$self->_meta = compact('class') + $self->_meta + $source['meta'];

		$self->_initializers += [
			'name' => function($self) {
				return basename(str_replace('\\', '/', $self));
			},
			'source' => function($self) {
				return Inflector::tableize($self::meta('name'));
			},
			'title' => function($self) {
				$titleKeys = ['title', 'name'];
				$titleKeys = array_merge($titleKeys, (array) $self::meta('key'));
				return $self::hasField($titleKeys);
			}
		];

		if (is_object($self->_schema)) {
			$self->_schema->append($source['schema']);
		} else {
			$self->_schema += $source['schema'];
		}

		$self->_finders += $source['finders'] + static::_finders();

		$self->_classes += [
			'query'       => 'lithium\data\model\Query',
			'validator'   => 'lithium\util\Validator',
			'entity'      => 'lithium\data\Entity'
		];

		static::_relationsToLoad();
		return $self;
	}

	/**
	 * Returns an instance of a class with given `config`. The `name` could be a key from the
	 * `classes` array, a fully-namespaced class name, or an object. Typically this method is used
	 * in `_init` to create the dependencies used in the current class.
	 *
	 * @param string|object $name A `classes` alias or fully-namespaced class name.
	 * @param array $options The configuration passed to the constructor.
	 * @return object
	 */
	protected static function _instance($name, array $options = []) {
		$self = static::_object();
		if (is_string($name) && isset($self->_classes[$name])) {
			$name = $self->_classes[$name];
		}
		return Libraries::instance(null, $name, $options);
	}

	/**
	 * Enables magic finders. These provide some syntactic-sugar which allows
	 * to i.e. use `Model::all()` instead  of `Model::find('all')`.
	 *
	 * ```
	 * // Retrieves post with id `23` using the `'first'` finder.
	 * Posts::first(['conditions' => ['id' => 23]]);
	 * Posts::findById(23);
	 * Posts::findById(23);
	 *
	 * // All posts that have a trueish `is_published` field.
	 * Posts::all(['conditions' => ['is_published' => true]]);
	 * Posts::findAll(['conditions' => ['is_published' => true]]);
	 * Posts::findAllByIsPublshed(true)
	 *
	 * // Counts all posts.
	 * Posts::count()
	 * ```
	 *
	 * @see lithium\data\Model::find()
	 * @see lithium\data\Model::$_meta
	 * @link http://php.net/language.oop5.overloading.php PHP Manual: Overloading
	 * @throws BadMethodCallException On unhandled call, will throw an exception.
	 * @param string $method Method name caught by `__callStatic()`.
	 * @param array $params Arguments given to the above `$method` call.
	 * @return mixed Results of dispatched `Model::find()` call.
	 */
	public static function __callStatic($method, $params) {
		$self = static::_object();

		if (isset($self->_finders[$method])) {
			if (count($params) === 2 && is_array($params[1])) {
				$params = [$params[1] + [$method => $params[0]]];
			}
			if ($params && !is_array($params[0])) {
				$params[0] = ['conditions' => static::key($params[0])];
			}
			return $self::find($method, $params ? $params[0] : []);
		}
		preg_match('/^findBy(?P<field>\w+)$|^find(?P<type>\w+)By(?P<fields>\w+)$/', $method, $args);

		if (!$args) {
			$message = "Method `%s` not defined or handled in class `%s`.";
			throw new BadMethodCallException(sprintf($message, $method, get_class($self)));
		}

		$field = Inflector::underscore($args['field'] ? $args['field'] : $args['fields']);
		$type = isset($args['type']) ? $args['type'] : 'first';
		$type[0] = strtolower($type[0]);

		$conditions = [$field => array_shift($params)];
		$params = (isset($params[0]) && count($params) === 1) ? $params[0] : $params;
		return $self::find($type, compact('conditions') + $params);
	}

	/**
	 * Magic method that allows calling `Model::_instanceMethods`'s closure like normal methods
	 * on the model instance.
	 *
	 * @see lithium\data\Model::instanceMethods
	 * @param string $method Method name caught by `__call()`.
	 * @param array $params Arguments given to the above `$method` call.
	 * @return mixed
	 */
	public function __call($method, $params) {
		$methods = static::instanceMethods();
		if (isset($methods[$method]) && is_callable($methods[$method])) {
			return call_user_func_array($methods[$method], $params);
		}
		$message = "Unhandled method call `{$method}`.";
		throw new BadMethodCallException($message);
	}

	/**
	 * Determines if a given method can be called.
	 *
	 * @param string $method Name of the method.
	 * @param boolean $internal Provide `true` to perform check from inside the
	 *                class/object. When `false` checks also for public visibility;
	 *                defaults to `false`.
	 * @return boolean Returns `true` if the method can be called, `false` otherwise.
	 */
	public static function respondsTo($method, $internal = false) {
		$self = static::_object();
		$methods = static::instanceMethods();
		$isFinder = isset($self->_finders[$method]);
		preg_match('/^findBy(?P<field>\w+)$|^find(?P<type>\w+)By(?P<fields>\w+)$/', $method, $args);
		$staticRepondsTo = $isFinder || $method === 'all' || !!$args;
		$instanceRespondsTo = isset($methods[$method]);
		return $instanceRespondsTo || $staticRepondsTo || parent::respondsTo($method, $internal);
	}

	/**
	 * The `find` method allows you to retrieve data from the connected data source.
	 *
	 * Examples:
	 * ```
	 * Posts::find('all'); // returns all records
	 * Posts::find('count'); // returns a count of all records
	 *
	 * // The first ten records that have `'author'` set to `'Bob'`.
	 * Posts::find('all', [
	 *     'conditions' => ['author' => 'Bob'],
	 *     'limit' => 10
	 * ]);
	 *
	 * // First record where the id matches 23.
	 * Posts::find('first', [
	 *     'conditions' => ['id' => 23]
	 * ]);
	 * ```
	 *
	 * Shorthands:
	 * ```
	 * // Shorthand for find first by primary key.
	 * Posts::find(23);
	 *
	 * // Also works with objects.
	 * Posts::find(new MongoId(23));
	 * ```
	 *
	 * @see lithium\data\Model::finder()
	 * @param string|object|integer $type The name of the finder to use. By default the
	 *        following finders are available. Custom finders can be added via `Model::finder()`.
	 *        - `'all'`: Returns all records matching the conditions.
	 *        - `'first'`: Returns the first record matching the conditions.
	 *        - `'count'`: Returns an integer count of all records matching the conditions.
	 *          When using `Database` adapter, you can specify the field to count on
	 *          via `fields`, when multiple fields are given does a count on all fields (`'*'`).
	 *        - `'list'`: Returns a one dimensional array, where the key is the (primary)p
	 *          key and the value the title of the record (the record must have a `'title'`
	 *          field). A result may look like: `[1 => 'Foo', 2 => 'Bar']`.
	 *
	 *        Instead of the name of a finder, also supports shorthand usage with an object or
	 *        integer as the first parameter. When passed such a value it is equal to
	 *        `Model::find('first', ['conditions' => ['<key>' => <value>]])`.
	 *
	 *        Note: When an undefined finder is tried to be used, the method will not error out, but
	 *        fallback to the `'all'` finder.
	 * @param array $options Options for the query.
	 *        Common options accepted are:
	 *        - `'conditions'` _array_: The conditions for the query
	 *           i.e. `'array('is_published' => true)`.
	 *        - `'fields'` _array|null_: The fields that should be retrieved. When set to
	 *          `null` or `'*'` and by default, uses all fields. To optimize query performance,
	 *          limit the fields to just the ones actually needed.
	 *        - `'order'` _array|string_: The order in which the data will be returned,
	 *           i.e. `'created ASC'` sorts by created date in ascending order. To sort by
	 *           multiple fields use the array syntax `array('title' => 'ASC', 'id' => 'ASC)`.
	 *        - `'limit'` _integer_: The maximum number of records to return.
	 *        - `'page'` _integer_: Allows to paginate data sets. Specifies the page of the set
	 *          together with the limit option specifying the number of records per page. The first
	 *          page starts at `1`. Equals limit * offset.
	 *        - `'with'` _array_: Relationship names to be included in the query.
	 *        Also supported are:
	 *        - `'offset'` _integer_
	 *        - `'having'` _array|string_
	 *        - `'group'` _array|string_
	 *        - `'joins'` _array_
	 * @return mixed The result/s of the find. Actual result depends on the finder being used. Most
	 *         often this is an instance of `lithium\data\Collection` or `lithium\data\Entity`.
	 * @filter Allows to execute logic before querying (i.e. for rewriting of $options)
	 *         or after i.e. for caching results.
	 */
	public static function find($type, array $options = []) {
		$self = static::_object();

		if (is_object($type) || !isset($self->_finders[$type])) {
			$options['conditions'] = static::key($type);
			$type = 'first';
		}

		$options += (array) $self->_query;
		$meta = ['meta' => $self->_meta, 'name' => get_called_class()];
		$params = compact('type', 'options');

		$implementation = function($params) use ($meta) {
			$options = $params['options'] + ['type' => 'read', 'model' => $meta['name']];
			$query = static::_instance('query', $options);

			return static::connection()->read($query, $options);
		};
		if (isset($self->_finders[$type])) {
			$finder = $self->_finders[$type];

			$reflect = new \ReflectionFunction($finder);
			if ($reflect->getNumberOfParameters() > 2) {
				$message  = 'Old style finder function in file ' . $reflect->getFileName() . ' ';
				$message .= 'on line ' . $reflect->getStartLine() . '. ';
				$message .= 'The signature for finder functions has changed. It is now ';
				$message .= '`($params, $next)` instead of the old `($self, $params, $chain)`. ';
				$message .= 'Instead of `$self` use `$this` or `static`.';
				trigger_error($message, E_USER_DEPRECATED);

				return Filters::bcRun(
					get_called_class(), __FUNCTION__, $params, $implementation, [$finder]
				);
			}

			$implementation = function($params) use ($finder, $implementation) {
				return $finder($params, $implementation);
			};
		}
		return Filters::run(get_called_class(), __FUNCTION__, $params, $implementation);
	}

	/**
	 * Sets or gets a custom finder by name. The finder definition can be an array of
	 * default query options, or an anonymous functions that accepts an array of query
	 * options, and a function to continue. To get a finder specify just the name.
	 *
	 * In this example we define and use `'published'` finder to quickly
	 * retrieve all published posts.
	 * ```
	 * Posts::finder('published', [
	 *     'conditions' => ['is_published' => true]
	 * ]);
	 *
	 * Posts::find('published');
	 * ```
	 *
	 * Here we define the same finder using an anonymous function which
	 * gives us more control over query modification.
	 * ```
	 * Posts::finder('published', function($params, $next) {
	 *     $params['options']['conditions']['is_published'] = true;
	 *
	 *     // Perform modifications before executing the query...
	 *     $result = $next($params);
	 *     // ... or after it has executed.
	 *
	 *     return $result;
	 * });
	 * ```
	 *
	 * When using finder array definitions the option array is _recursivly_ merged
	 * (using `Set::merge()`) with additional options specified on the `Model::find()`
	 * call. Options specificed on the find will overwrite options specified in the
	 * finder.
	 *
	 * Array finder definitions are normalized here, so that it can be relied upon that defined
	 * finders are always anonymous functions.
	 *
	 * @see lithium\util\Set::merge()
	 * @param string $name The finder name, e.g. `'first'`.
	 * @param string|callable|null $finder The finder definition.
	 * @return callable|void Returns finder definition if querying, or void if setting.
	 */
	public static function finder($name, $finder = null) {
		$self = static::_object();

		if ($finder === null) {
			return isset($self->_finders[$name]) ? $self->_finders[$name] : null;
		}
		if (is_array($finder)) {
			$finder = function($params, $next) use ($finder) {
				$params['options'] = Set::merge($params['options'], $finder);
				return $next($params);
			};
		}
		$self->_finders[$name] = $finder;
	}

	/**
	 * Returns an array with the default finders.
	 *
	 * @see lithium\data\Model::_initialize()
	 * @return array
	 */
	protected static function _finders() {
		$self = static::_object();

		return [
			'all' => function($params, $next) {
				return $next($params);
			},
			'first' => function($params, $next) {
				$options =& $params['options'];
				$options['limit'] = 1;

				$data = $next($params);

				if (isset($options['return']) && $options['return'] === 'array') {
					$data = is_array($data) ? reset($data) : $data;
				} else {
					$data = is_object($data) ? $data->rewind() : $data;
				}
				return $data ?: null;
			},
			'list' => function($params, $next) use ($self) {
				$result = [];
				$meta = $self::meta();
				$name = $meta['key'];

				foreach ($next($params) as $entity) {
					$key = $entity->{$name};
					$result[is_scalar($key) ? $key : (string) $key] = $entity->title();
				}
				return $result;
			},
			'count' => function($params, $next) use ($self) {
				$options = array_diff_key($params['options'], $self->_query);

				if ($options && !isset($params['options']['conditions'])) {
					$options = ['conditions' => $options];
				} else {
					$options = $params['options'];
				}
				$options += ['type' => 'read', 'model' => $self];
				$query = $self::invokeMethod('_instance', ['query', $options]);
				return $self::connection()->calculation('count', $query, $options);
			}
		];
	}

	/**
	 * Gets or sets the default query for the model.
	 *
	 * @param array $query Possible options are:
	 *        - `'conditions'`: The conditional query elements, e.g.
	 *          `'conditions' => ['published' => true]`
	 *        - `'fields'`: The fields that should be retrieved. When set to `null`, defaults to
	 *          all fields.
	 *        - `'order'`: The order in which the data will be returned, e.g. `'order' => 'ASC'`.
	 *        - `'limit'`: The maximum number of records to return.
	 *        - `'page'`: For pagination of data.
	 *        - `'with'`: An array of relationship names to be included in the query.
	 * @return mixed Returns the query definition if querying, or `null` if setting.
	 */
	public static function query($query = null) {
		$self = static::_object();

		if (!$query) {
			return $self->_query;
		}
		$self->_query = $query + $self->_query;
	}

	/**
	 * Gets or sets Model's metadata.
	 *
	 * @see lithium\data\Model::$_meta
	 * @param string $key Model metadata key.
	 * @param string $value Model metadata value.
	 * @return mixed Metadata value for a given key.
	 */
	public static function meta($key = null, $value = null) {
		$self = static::_object();
		$isArray = is_array($key);

		if ($value || $isArray) {
			$value ? $self->_meta[$key] = $value : $self->_meta = $key + $self->_meta;
			return;
		}
		return $self->_getMetaKey($isArray ? null : $key);
	}

	/**
	 * Helper method used by `meta()` to generate and cache metadata values.
	 *
	 * @param string $key The name of the meta value to return, or `null`, to return all values.
	 * @return mixed Returns the value of the meta key specified by `$key`, or an array of all meta
	 *         values if `$key` is `null`.
	 */
	protected function _getMetaKey($key = null) {
		if (!$key) {
			$all = array_keys($this->_initializers);
			$call = [&$this, '_getMetaKey'];
			return $all ? array_combine($all, array_map($call, $all)) + $this->_meta : $this->_meta;
		}

		if (isset($this->_meta[$key])) {
			return $this->_meta[$key];
		}
		if (isset($this->_initializers[$key]) && $initializer = $this->_initializers[$key]) {
			unset($this->_initializers[$key]);
			return ($this->_meta[$key] = $initializer(get_called_class()));
		}
	}

	/**
	 * The `title()` method is invoked whenever an `Entity` object is cast or coerced
	 * to a string. This method can also be called on the entity directly, i.e. `$post->title()`.
	 *
	 * By default, when generating the title for an object, it uses the the field specified in
	 * the `'title'` key of the model's meta data definition. Override this method to generate
	 * custom titles for objects of this model's type.
	 *
	 * @see lithium\data\Model::$_meta
	 * @see lithium\data\Entity::__toString()
	 * @param object $entity The `Entity` instance on which the title method is called.
	 * @return string Returns the title representation of the entity on which this method is called.
	 */
	public function title($entity) {
		$field = static::meta('title');
		return $entity->{$field};
	}

	/**
	 * If no values supplied, returns the name of the `Model` key. If values
	 * are supplied, returns the key value.
	 *
	 * @param mixed $values An array of values or object with values. If `$values` is `null`,
	 *              the meta `'key'` of the model is returned.
	 * @return mixed Key value.
	 */
	public static function key($values = null) {
		$key = static::meta('key');

		if ($values === null) {
			return $key;
		}

		$self = static::_object();
		$entity = $self->_classes['entity'];
		if (is_object($values) && is_string($key)) {
			return static::_key($key, $values, $entity);
		} elseif ($values instanceof $entity) {
			$values = $values->to('array');
		}

		if (!is_array($values) && !is_array($key)) {
			return [$key => $values];
		}

		$key = (array) $key;
		$result = [];
		foreach ($key as $value) {
			if (!isset($values[$value])) {
				return null;
			}
			$result[$value] = $values[$value];
		}
		return $result;
	}

	/**
	 * Helper for the `Model::key()` function
	 *
	 * @see lithium\data\Model::key()
	 * @param string $key The key
	 * @param object $values Object with attributes.
	 * @param string $entity The fully-namespaced entity class name.
	 * @return mixed The key value array or `null` if the `$values` object has no attribute
	 *         named `$key`
	 */
	protected static function _key($key, $values, $entity) {
		if (isset($values->$key)) {
			return [$key => $values->$key];
		} elseif (!$values instanceof $entity) {
			return [$key => $values];
		}
		return null;
	}

	/**
	 * Returns a list of models related to `Model`, or a list of models related
	 * to this model, but of a certain type.
	 *
	 * @param string $type A type of model relation.
	 * @return array|object|void An array of relation instances or an instance of relation.
	 */
	public static function relations($type = null) {
		$self = static::_object();

		if ($type === null) {
			return static::_relations();
		}
		if (isset($self->_relationFieldNames[$type])) {
			$type = $self->_relationFieldNames[$type];
		}

		if (isset($self->_relations[$type])) {
			return $self->_relations[$type];
		}
		if (isset($self->_relationsToLoad[$type])) {
			return static::_relations(null, $type);
		}
		if (in_array($type, $self->_relationTypes, true)) {
			return array_keys(static::_relations($type));
		}
	}

	/**
	 * This method automagically bind in the fly unloaded relations.
	 *
	 * @see lithium\data\Model::relations()
	 * @param $type A type of model relation.
	 * @param $name A relation name.
	 * @return An array of relation instances or an instance of relation.
	 */
	protected static function _relations($type = null, $name = null) {
		$self = static::_object();

		if ($name) {
			if (isset($self->_relationsToLoad[$name])) {
				$t = $self->_relationsToLoad[$name];
				unset($self->_relationsToLoad[$name]);
				return static::bind($t, $name, (array) $self->{$t}[$name]);
			}
			return isset($self->_relations[$name]) ? $self->_relations[$name] : null;
		}
		if (!$type) {
			foreach ($self->_relationsToLoad as $name => $t) {
				static::bind($t, $name, (array) $self->{$t}[$name]);
			}
			$self->_relationsToLoad = [];
			return $self->_relations;
		}
		foreach ($self->_relationsToLoad as $name => $t) {
			if ($type === $t) {
				static::bind($t, $name, (array) $self->{$t}[$name]);
				unset($self->_relationsToLoad[$name]);
			}
		}
		return array_filter($self->_relations, function($i) use ($type) {
			return $i->data('type') === $type;
		});
	}

	/**
	 * Creates a relationship binding between this model and another.
	 *
	 * @see lithium\data\model\Relationship
	 * @param string $type The type of relationship to create. Must be one of `'hasOne'`,
	 *               `'hasMany'` or `'belongsTo'`.
	 * @param string $name The name of the relationship. If this is also the name of the model,
	 *               the model must be in the same namespace as this model. Otherwise, the
	 *               fully-namespaced path to the model class must be specified in `$config`.
	 * @param array $config Any other configuration that should be specified in the relationship.
	 *              See the `Relationship` class for more information.
	 * @return object Returns an instance of the `Relationship` class that defines the connection.
	 */
	public static function bind($type, $name, array $config = []) {
		$self = static::_object();
		if (!isset($config['fieldName'])) {
			$config['fieldName'] = $self->_relationFieldName($type, $name);
		}

		if (!in_array($type, $self->_relationTypes)) {
			throw new ConfigException("Invalid relationship type `{$type}` specified.");
		}
		$self->_relationFieldNames[$config['fieldName']] = $name;
		$rel = static::connection()->relationship(get_called_class(), $type, $name, $config);
		return $self->_relations[$name] = $rel;
	}

	/**
	 * Lazy-initialize the schema for this Model object, if it is not already manually set in the
	 * object. You can declare `protected $_schema = [...]` to define the schema manually.
	 *
	 * @param mixed $field Optional. You may pass a field name to get schema information for just
	 *        one field. Otherwise, an array containing all fields is returned. If `false`, the
	 *        schema is reset to an empty value. If an array, field definitions contained are
	 *        appended to the schema.
	 * @return array|lithium\data\Schema
	 */
	public static function schema($field = null) {
		$self = static::_object();

		if (!is_object($self->_schema)) {
			$self->_schema = static::connection()->describe(
				$self::meta('source'), $self->_schema, $self->_meta
			);
			if (!is_object($self->_schema)) {
				$class = get_called_class();
				throw new ConfigException("Could not load schema object for model `{$class}`.");
			}
			$key = (array) $self::meta('key');
			if ($self->_schema && $self->_schema->fields() && !$self->_schema->has($key)) {
				$key = implode('`, `', $key);
				throw new ConfigException("Missing key `{$key}` from schema.");
			}
		}
		if ($field === false) {
			return $self->_schema->reset();
		}
		if (is_array($field)) {
			return $self->_schema->append($field);
		}
		return $field ? $self->_schema->fields($field) : $self->_schema;
	}

	/**
	 * Checks to see if a particular field exists in a model's schema. Can check a single field, or
	 * return the first field found in an array of multiple options.
	 *
	 * @param mixed $field A single field (string) or list of fields (array) to check the existence
	 *        of.
	 * @return mixed If `$field` is a string, returns a boolean indicating whether or not that field
	 *         exists. If `$field` is an array, returns the first field found, or `false` if none of
	 *         the fields in the list are found.
	 */
	public static function hasField($field) {
		if (!is_array($field)) {
			return static::schema()->fields($field);
		}
		foreach ($field as $f) {
			if (static::hasField($f)) {
				return $f;
			}
		}
		return false;
	}

	/**
	 * Instantiates a new record or document object, initialized with any data passed in. For
	 * example:
	 *
	 * ```
	 * $post = Posts::create(['title' => 'New post']);
	 * echo $post->title; // echoes 'New post'
	 * $success = $post->save();
	 * ```
	 *
	 * Note that while this method creates a new object, there is no effect on the database until
	 * the `save()` method is called.
	 *
	 * In addition, this method can be used to simulate loading a pre-existing object from the
	 * database, without actually querying the database:
	 *
	 * ```
	 * $post = Posts::create(['id' => $id, 'moreData' => 'foo'], ['exists' => true]);
	 * $post->title = 'New title';
	 * $success = $post->save();
	 * ```
	 *
	 * This will create an update query against the object with an ID matching `$id`. Also note that
	 * only the `title` field will be updated.
	 *
	 * @param array $data Any data that this object should be populated with initially.
	 * @param array $options Options to be passed to item.
	 * @return object Returns a new, _un-saved_ record or document object. In addition to the values
	 *         passed to `$data`, the object will also contain any values assigned to the
	 *         `'default'` key of each field defined in `$_schema`.
	 * @filter
	 */
	public static function create(array $data = [], array $options = []) {
		$defaults = ['defaults' => true, 'class' => 'entity'];
		$options += $defaults;

		$params = compact('data', 'options');

		return Filters::run(get_called_class(), __FUNCTION__, $params, function($params) {
			$class = $params['options']['class'];
			unset($params['options']['class']);
			if ($class === 'entity' && $params['options']['defaults']) {
				$data = Set::merge(Set::expand(static::schema()->defaults()), $params['data']);
			} else {
				$data = $params['data'];
			}
			return static::_instance($class, [
				'model' => get_called_class(),
				'data' => $data
			] + $params['options']);
		});
	}

	/**
	 * Getter and setter for custom instance methods. This is used in `Entity::__call()`.
	 *
	 * ```
	 * Model::instanceMethods([
	 *     'methodName' => ['Class', 'method'],
	 *     'anotherMethod' => [$object, 'method'],
	 *     'closureCallback' => function($entity) {}
	 * ]);
	 * ```
	 *
	 * @see lithium\data\Entity::__call()
	 * @param array $methods
	 * @return array
	 */
	public static function instanceMethods(array $methods = null) {
		$class = get_called_class();

		if (!isset(static::$_instanceMethods[$class])) {
			static::$_instanceMethods[$class] = [];
		}
		if ($methods === []) {
			return static::$_instanceMethods[$class] = [];
		}
		if ($methods !== null) {
			static::$_instanceMethods[$class] = $methods + static::$_instanceMethods[$class];
		}
		return static::$_instanceMethods[$class];
	}

	/**
	 * An instance method (called on record and document objects) to create or update the record or
	 * document in the database that corresponds to `$entity`.
	 *
	 * For example, to create a new record or document:
	 * ```
	 * $post = Posts::create(); // Creates a new object, which doesn't exist in the database yet
	 * $post->title = "My post";
	 * $success = $post->save();
	 * ```
	 *
	 * It is also used to update existing database objects, as in the following:
	 * ```
	 * $post = Posts::first($id);
	 * $post->title = "Revised title";
	 * $success = $post->save();
	 * ```
	 *
	 * By default, an object's data will be checked against the validation rules of the model it is
	 * bound to. Any validation errors that result can then be accessed through the `errors()`
	 * method.
	 *
	 * ```
	 * if (!$post->save($someData)) {
	 *     return ['errors' => $post->errors()];
	 * }
	 * ```
	 *
	 * To override the validation checks and save anyway, you can pass the `'validate'` option:
	 *
	 * ```
	 * $post->title = "We Don't Need No Stinkin' Validation";
	 * $post->body = "I know what I'm doing.";
	 * $post->save(null, ['validate' => false]);
	 * ```
	 *
	 * By default only validates and saves fields from the schema (if available). This behavior
	 * can be controlled via the `'whitelist'` and `'locked'` options.
	 *
	 * @see lithium\data\Model::$validates
	 * @see lithium\data\Model::validates()
	 * @see lithium\data\Entity::errors()
	 * @param object $entity The record or document object to be saved in the database. This
	 *        parameter is implicit and should not be passed under normal circumstances.
	 *        In the above example, the call to `save()` on the `$post` object is
	 *        transparently proxied through to the `Posts` model class, and `$post` is passed
	 *        in as the `$entity` parameter.
	 * @param array $data Any data that should be assigned to the record before it is saved.
	 * @param array $options Options:
	 *        - `'callbacks'` _boolean_: If `false`, all callbacks will be disabled before
	 *           executing. Defaults to `true`.
	 *        - `'validate'` _boolean|array_: If `false`, validation will be skipped, and the
	 *          record will be immediately saved. Defaults to `true`. May also be specified as
	 *          an array, in which case it will replace the default validation rules specified
	 *          in the `$validates` property of the model.
	 *        - `'events'` _string|array_: A string or array defining one or more validation
	 *          _events_. Events are different contexts in which data events can occur, and
	 *          correspond to the optional `'on'` key in validation rules. They will be passed
	 *          to the validates() method if `'validate'` is not `false`.
	 *        - `'whitelist'` _array_: An array of fields that are allowed to be saved to this
	 *          record. When unprovided will - if available - default to fields of the current
	 *          schema and the `'locked'` option is not `false`.
	 *        - `'locked'` _boolean_: Whether to use schema for saving just fields from the
	 *          schema or not. Defaults to `true`.
	 * @return boolean Returns `true` on a successful save operation, `false` on failure.
	 * @filter
	 */
	public function save($entity, $data = null, array $options = []) {
		$self = static::_object();
		$_meta = ['model' => get_called_class()] + $self->_meta;
		$_schema = $self->schema();

		$defaults = [
			'validate' => true,
			'events' => $entity->exists() ? 'update' : 'create',
			'whitelist' => null,
			'callbacks' => true,
			'locked' => $self->_meta['locked']
		];
		$options += $defaults;
		$params = compact('entity', 'data', 'options');

		$filter = function($params) use ($_meta, $_schema) {
			$entity = $params['entity'];
			$options = $params['options'];

			if ($params['data']) {
				$entity->set($params['data']);
			}
			if (($whitelist = $options['whitelist']) || $options['locked']) {
				$whitelist = $whitelist ?: array_keys($_schema->fields());
			}
			if ($rules = $options['validate']) {
				$events = $options['events'];
				$validateOpts = compact('events', 'whitelist');
				if (is_array($rules)) {
					$validateOpts['rules'] = $rules;
				}

				if (!$entity->validates($validateOpts)) {
					return false;
				}
			}
			$type = $entity->exists() ? 'update' : 'create';

			$query = static::_instance('query',
				compact('type', 'whitelist', 'entity') + $options + $_meta
			);
			return static::connection()->{$type}($query, $options);
		};

		if (!$options['callbacks']) {
			return $filter($params);
		}
		return Filters::run(get_called_class(), __FUNCTION__, $params, $filter);
	}

	/**
	 * An important part of describing the business logic of a model class is defining the
	 * validation rules. In Lithium models, rules are defined through the `$validates` class
	 * property, and are used by this method before saving to verify the correctness of the data
	 * being sent to the backend data source.
	 *
	 * Note that these are application-level validation rules, and do not
	 * interact with any rules or constraints defined in your data source. If such constraints fail,
	 * an exception will be thrown by the database layer. The `validates()` method only checks
	 * against the rules defined in application code.
	 *
	 * This method uses the `Validator` class to perform data validation. An array representation of
	 * the entity object to be tested is passed to the `check()` method, along with the model's
	 * validation rules. Any rules defined in the `Validator` class can be used to validate fields.
	 * See the `Validator` class to add custom rules, or override built-in rules.
	 *
	 * @see lithium\data\Model::$validates
	 * @see lithium\util\Validator::check()
	 * @see lithium\data\Entity::errors()
	 * @param object $entity Model entity to validate. Typically either a `Record` or `Document`
	 *        object. In the following example:
	 *        ```
	 *            $post = Posts::create($data);
	 *            $success = $post->validates();
	 *        ```
	 *        The `$entity` parameter is equal to the `$post` object instance.
	 * @param array $options Available options:
	 *        - `'rules'` _array_: If specified, this array will _replace_ the default
	 *          validation rules defined in `$validates`.
	 *        - `'events'` _mixed_: A string or array defining one or more validation
	 *          _events_. Events are different contexts in which data events can occur, and
	 *          correspond to the optional `'on'` key in validation rules. For example, by
	 *          default, `'events'` is set to either `'create'` or `'update'`, depending on
	 *          whether `$entity` already exists. Then, individual rules can specify
	 *          `'on' => 'create'` or `'on' => 'update'` to only be applied at certain times.
	 *          Using this parameter, you can set up custom events in your rules as well, such
	 *          as `'on' => 'login'`. Note that when defining validation rules, the `'on'` key
	 *          can also be an array of multiple events.
	 *        - `'required`' _mixed_: Represents whether the value is required to be present
	 *          in `$values`. If `'required'` is set to `true`, the validation rule will be
	 *          checked. if `'required'` is set to 'false' , the validation rule will be skipped
	 *          if the corresponding key is not present. If don't set `'required'` or set this
	 *          to `null`, the validation rule will be skipped if the corresponding key is not
	 *          present in update and will be checked in insert. Defaults is set to `null`.
	 *        - `'whitelist'` _array_: If specified, only fields in this array will be validated
	 *          and others will be skipped.
	 * @return boolean Returns `true` if all validation rules on all fields succeed, otherwise
	 *         `false`. After validation, the messages for any validation failures are assigned to
	 *         the entity, and accessible through the `errors()` method of the entity object.
	 * @filter
	 */
	public function validates($entity, array $options = []) {
		$defaults = [
			'rules' => $this->validates,
			'events' => $entity->exists() ? 'update' : 'create',
			'model' => get_called_class(),
			'required' => null,
			'whitelist' => null
		];
		$options += $defaults;

		if ($options['required'] === null) {
			$options['required'] = !$entity->exists();
		}
		$self = static::_object();
		$validator = $self->_classes['validator'];
		$entity->errors(false);
		$params = compact('entity', 'options');

		$implementation = function($params) use ($validator) {
			$entity = $params['entity'];
			$options = $params['options'];
			$rules = $options['rules'];
			unset($options['rules']);
			if ($whitelist = $options['whitelist']) {
				$whitelist = array_combine($whitelist, $whitelist);
				$rules = array_intersect_key($rules, $whitelist);
			}

			if ($errors = $validator::check($entity->data(), $rules, $options)) {
				$entity->errors($errors);
			}
			return empty($errors);
		};
		return Filters::run(get_called_class(), __FUNCTION__, $params, $implementation);
	}

	/**
	 * Deletes the data associated with the current `Model`.
	 *
	 * @param object $entity Entity to delete.
	 * @param array $options Options.
	 * @return boolean Success.
	 * @filter Good for executing logic for i.e. invalidating cached results.
	 */
	public function delete($entity, array $options = []) {
		$params = compact('entity', 'options');

		return Filters::run(get_called_class(), __FUNCTION__, $params, function($params) {
			$options = $params + $params['options'] + [
				'model' => get_called_class(),
				'type' => 'delete'
			];
			unset($options['options']);

			$query = static::_instance('query', $options);
			return static::connection()->delete($query, $options);
		});
	}

	/**
	 * Update multiple records or documents with the given data, restricted by the given set of
	 * criteria (optional).
	 *
	 * @param mixed $data Typically an array of key/value pairs that specify the new data with which
	 *              the records will be updated. For SQL databases, this can optionally be an SQL
	 *              fragment representing the `SET` clause of an `UPDATE` query.
	 * @param mixed $conditions An array of key/value pairs representing the scope of the records
	 *              to be updated.
	 * @param array $options Any database-specific options to use when performing the operation. See
	 *              the `delete()` method of the corresponding backend database for available
	 *              options.
	 * @return boolean Returns `true` if the update operation succeeded, otherwise `false`.
	 * @filter
	 */
	public static function update($data, $conditions = [], array $options = []) {
		$params = compact('data', 'conditions', 'options');

		return Filters::run(get_called_class(), __FUNCTION__, $params, function($params) {
			$options = $params + $params['options'] + [
				'model' => get_called_class(),
				'type' => 'update'
			];
			unset($options['options']);

			$query = static::_instance('query', $options);
			return static::connection()->update($query, $options);
		});
	}

	/**
	 * Remove multiple documents or records based on a given set of criteria. **WARNING**: If no
	 * criteria are specified, or if the criteria (`$conditions`) is an empty value (i.e. an empty
	 * array or `null`), all the data in the backend data source (i.e. table or collection) _will_
	 * be deleted.
	 *
	 * @param mixed $conditions An array of key/value pairs representing the scope of the records or
	 *              documents to be deleted.
	 * @param array $options Any database-specific options to use when performing the operation. See
	 *              the `delete()` method of the corresponding backend database for available
	 *              options.
	 * @return boolean Returns `true` if the remove operation succeeded, otherwise `false`.
	 * @filter
	 */
	public static function remove($conditions = [], array $options = []) {
		$params = compact('conditions', 'options');

		return Filters::run(get_called_class(), __FUNCTION__, $params, function($params) {
			$options = $params['options'] + $params + [
				'model' => get_called_class(),
				'type' => 'delete'
			];
			unset($options['options']);

			$query = static::_instance('query', $options);
			return static::connection()->delete($query, $options);
		});
	}

	/**
	 * Gets the connection object to which this model is bound. Throws exceptions if a connection
	 * isn't set, or if the connection named isn't configured.
	 *
	 * @return object Returns an instance of `lithium\data\Source` from the connection configuration
	 *         to which this model is bound.
	 */
	public static function &connection() {
		$self = static::_object();
		$connections = $self->_classes['connections'];
		$name = isset($self->_meta['connection']) ? $self->_meta['connection'] : null;

		if ($conn = $connections::get($name)) {
			return $conn;
		}
		$class = get_called_class();
		$msg = "The data connection `{$name}` is not configured for model `{$class}`.";
		throw new ConfigException($msg);
	}

	protected static function &_object() {
		$class = get_called_class();

		if (!isset(static::$_instances[$class])) {
			static::$_instances[$class] = new $class();
			static::config();
		}
		$object = static::_initialize($class);
		return $object;
	}

	/**
	 * Iterates through relationship types to construct relation map.
	 *
	 * @todo See if this can be rewritten to be lazy.
	 * @return void
	 */
	protected static function _relationsToLoad() {
		try {
			if (!$connection = static::connection()) {
				return;
			}
		} catch (ConfigException $e) {
			return;
		}

		if (!$connection::enabled('relationships')) {
			return;
		}

		$self = static::_object();

		foreach ($self->_relationTypes as $type) {
			$self->$type = Set::normalize($self->$type);
			foreach ($self->$type as $name => $config) {
				$self->_relationsToLoad[$name] = $type;
				$fieldName = $self->_relationFieldName($type, $name);
				$self->_relationFieldNames[$fieldName] = $name;
			}
		}
	}

	protected function _relationFieldName($type, $name) {
		if (!isset($this->{$type}[$name]['fieldName'])) {
			$fieldName = static::connection()->relationFieldName($type, $name);
			$this->{$type}[$name]['fieldName'] = $fieldName;
		}
		return $this->{$type}[$name]['fieldName'];
	}

	/**
	 * Eager loads relations.
	 *
	 * @param mixed $collection The collection to extend.
	 * @param array $relations The relations to eager load.
	 * @return mixed The collection.
	 */
	public static function embed(&$collection, $relations) {
		$tree = Set::expand(array_fill_keys(array_keys(Set::normalize($relations)), []));

		foreach ($tree as $name => $subtree) {
			$rel = static::relations($name);
			$to = $rel->to();
			$related = $rel->embed($collection, isset($relations[$name]) ? $relations[$name] : []);

			$subrelations = [];
			foreach ($relations as $path => $value) {
				if (preg_match('~^'.$name.'\.(.*)$~', $path, $matches)) {
					$subrelations[] = $matches[1];
				}
			}
			if ($subrelations) {
				$to::embed($related, $subrelations);
			}
		}
		return $collection;
	}

	/**
	 * Resetting the model.
	 */
	public static function reset() {
		$class = get_called_class();
		unset(static::$_instances[$class]);
	}
}