# 模型元數據（Models Metadata） To speed up development[Phalcon\\Mvc\\Model](http://docs.iphalcon.cn/api/Phalcon_Mvc_Model.html)helps you to query fields and constraints from tables related to models. To achieve this,[Phalcon\\Mvc\\Model\\MetaData](http://docs.iphalcon.cn/api/Phalcon_Mvc_Model_MetaData.html)is available to manage and cache table metadata. Sometimes it is necessary to get those attributes when working with models. You can get a metadata instance as follows: ~~~ <?php $robot = new Robots(); // Get Phalcon\Mvc\Model\Metadata instance $metadata = $robot->getModelsMetaData(); // Get robots fields names $attributes = $metadata->getAttributes($robot); print_r($attributes); // Get robots fields data types $dataTypes = $metadata->getDataTypes($robot); print_r($dataTypes); ~~~ ## 緩存元數據（Caching Metadata） Once the application is in a production stage, it is not necessary to query the metadata of the table from the database system each time you use the table. This could be done caching the metadata using any of the following adapters: | Adapter | Description | API | | --- | --- | --- | | Memory | This adapter is the default. The metadata is cached only during the request. When the request is completed, the metadata are released as part of the normal memory of the request. This adapter is perfect when the application is in development so as to refresh the metadata in each request containing the new and/or modified fields. | [Phalcon\\Mvc\\Model\\MetaData\\Memory](http://docs.iphalcon.cn/api/Phalcon_Mvc_Model_MetaData_Memory.html) | | Session | This adapter stores metadata in the`$_SESSION`superglobal. This adapter is recommended only when the application is actually using a small number of models. The metadata are refreshed every time a new session starts. This also requires the use of`session_start()`to start the session before using any models. | [Phalcon\\Mvc\\Model\\MetaData\\Session](http://docs.iphalcon.cn/api/Phalcon_Mvc_Model_MetaData_Session.html) | | Apc | This adapter uses the[Alternative PHP Cache (APC)](http://www.php.net/manual/zh/book.apc.php)to store the table metadata. You can specify the lifetime of the metadata with options. This is the most recommended way to store metadata when the application is in production stage. | [Phalcon\\Mvc\\Model\\MetaData\\Apc](http://docs.iphalcon.cn/api/Phalcon_Mvc_Model_MetaData_Apc.html) | | XCache | This adapter uses[XCache](http://xcache.lighttpd.net/)to store the table metadata. You can specify the lifetime of the metadata with options. This is the most recommended way to store metadata when the application is in production stage. | [Phalcon\\Mvc\\Model\\MetaData\\Xcache](http://docs.iphalcon.cn/api/Phalcon_Mvc_Model_MetaData_Xcache.html) | | Files | This adapter uses plain files to store metadata. By using this adapter the disk-reading is increased but the database access is reduced. | [Phalcon\\Mvc\\Model\\MetaData\\Files](http://docs.iphalcon.cn/api/Phalcon_Mvc_Model_MetaData_Files.html) | As other ORM’s dependencies, the metadata manager is requested from the services container: ~~~ <?php use Phalcon\Mvc\Model\MetaData\Apc as ApcMetaData; $di["modelsMetadata"] = function () { // Create a metadata manager with APC $metadata = new ApcMetaData( [ "lifetime" => 86400, "prefix" => "my-prefix", ] ); return $metadata; }; ~~~ ## 元數據策略（Metadata Strategies） As mentioned above the default strategy to obtain the model’s metadata is database introspection. In this strategy, the information schema is used to know the fields in a table, its primary key, nullable fields, data types, etc. You can change the default metadata introspection in the following way: ~~~ <?php use Phalcon\Mvc\Model\MetaData\Apc as ApcMetaData; $di["modelsMetadata"] = function () { // Instantiate a metadata adapter $metadata = new ApcMetaData( [ "lifetime" => 86400, "prefix" => "my-prefix", ] ); // Set a custom metadata introspection strategy $metadata->setStrategy( new MyIntrospectionStrategy() ); return $metadata; }; ~~~ ### 數據庫內部策略（Database Introspection Strategy） This strategy doesn’t require any customization and is implicitly used by all the metadata adapters. ### 注釋策略（Annotations Strategy） This strategy makes use of[annotations](http://docs.iphalcon.cn/reference/annotations.html)to describe the columns in a model: ~~~ <?php use Phalcon\Mvc\Model; class Robots extends Model { /** * @Primary * @Identity * @Column(type="integer", nullable=false) */ public $id; /** * @Column(type="string", length=70, nullable=false) */ public $name; /** * @Column(type="string", length=32, nullable=false) */ public $type; /** * @Column(type="integer", nullable=false) */ public $year; } ~~~ Annotations must be placed in properties that are mapped to columns in the mapped source. Properties without the @Column annotation are handled as simple class attributes. The following annotations are supported: | Name | Description | | --- | --- | | Primary | Mark the field as part of the table’s primary key | | Identity | The field is an auto\_increment/serial column | | Column | This marks an attribute as a mapped column | The annotation @Column supports the following parameters: | Name | Description | | --- | --- | | type | The column’s type (string, integer, decimal, boolean) | | length | The column’s length if any | | nullable | Set whether the column accepts null values or not | The annotations strategy could be set up this way: ~~~ <?php use Phalcon\Mvc\Model\MetaData\Apc as ApcMetaData; use Phalcon\Mvc\Model\MetaData\Strategy\Annotations as StrategyAnnotations; $di["modelsMetadata"] = function () { // Instantiate a metadata adapter $metadata = new ApcMetaData( [ "lifetime" => 86400, "prefix" => "my-prefix", ] ); // Set a custom metadata database introspection $metadata->setStrategy( new StrategyAnnotations() ); return $metadata; }; ~~~ ## 自定義元數據（Manual Metadata） Phalcon can obtain the metadata for each model automatically without the developer must set them manually using any of the introspection strategies presented above. The developer also has the option of define the metadata manually. This strategy overrides any strategy set in the metadata manager. New columns added/modified/removed to/from the mapped table must be added/modified/removed also for everything to work properly. The following example shows how to define the metadata manually: ~~~ <?php use Phalcon\Mvc\Model; use Phalcon\Db\Column; use Phalcon\Mvc\Model\MetaData; class Robots extends Model { public function metaData() { return array( // Every column in the mapped table MetaData::MODELS_ATTRIBUTES => [ "id", "name", "type", "year", ], // Every column part of the primary key MetaData::MODELS_PRIMARY_KEY => [ "id", ], // Every column that isn't part of the primary key MetaData::MODELS_NON_PRIMARY_KEY => [ "name", "type", "year", ], // Every column that doesn't allows null values MetaData::MODELS_NOT_NULL => [ "id", "name", "type", ], // Every column and their data types MetaData::MODELS_DATA_TYPES => [ "id" => Column::TYPE_INTEGER, "name" => Column::TYPE_VARCHAR, "type" => Column::TYPE_VARCHAR, "year" => Column::TYPE_INTEGER, ], // The columns that have numeric data types MetaData::MODELS_DATA_TYPES_NUMERIC => [ "id" => true, "year" => true, ], // The identity column, use boolean false if the model doesn't have // an identity column MetaData::MODELS_IDENTITY_COLUMN => "id", // How every column must be bound/casted MetaData::MODELS_DATA_TYPES_BIND => [ "id" => Column::BIND_PARAM_INT, "name" => Column::BIND_PARAM_STR, "type" => Column::BIND_PARAM_STR, "year" => Column::BIND_PARAM_INT, ], // Fields that must be ignored from INSERT SQL statements MetaData::MODELS_AUTOMATIC_DEFAULT_INSERT => [ "year" => true, ], // Fields that must be ignored from UPDATE SQL statements MetaData::MODELS_AUTOMATIC_DEFAULT_UPDATE => [ "year" => true, ], // Default values for columns MetaData::MODELS_DEFAULT_VALUES => [ "year" => "2015", ], // Fields that allow empty strings MetaData::MODELS_EMPTY_STRING_VALUES => [ "name" => true, ], ); } } ~~~