Eloquent： 修改器

感受好長時間沒寫東西了，一方面主要是本身的角色發生了變化，天天要面對各類各樣的事情和突發事件，不能再有一個完整的長時間讓本身靜下來寫代碼，或者寫文章。

另外一方面如今公司技術棧再也不停留在只有 Laravel + VUE 了，咱們還有小程序、APP 等開發，因此我關注的東西也就多了。

接下來我仍是會繼續持續「高產」，把寫技術文章看成一個習慣，堅持下去。

好了，廢話很少說，今天來講一說「Eloquent： 修改器」。

一直想好好研究下 Eloquent。但苦於 Eloquent 有太多可研究的，沒法找到一個切入點。前兩天看一同事好像對這個「Eloquent： 修改器」瞭解很少，因此今天就拿它做爲入口，扒一扒其實現源代碼。

首先仍是拿一個 Demo 爲例：

Demo

<?php
namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Carbon\Carbon;

class Baby extends Model {
    protected $table = 'baby';
    protected $appends = ['age'];

    public function getAgeAttribute() {
        $date = new Carbon($this->birthday);
        return Carbon::now()->diffInYears($date);
    }
}
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這個代碼比較簡單，就是經過已有屬性 birthday，計算 Baby 幾歲了，獲得 age 屬性。

前端就能夠直接拿到結果：

return $baby->age;
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一樣的，還有 setXxxAttribute 方法來定義一個修改器。

源代碼

讀代碼仍是從使用入手，如上經過 $baby->age 調用 age 屬性，這個屬性沒在類中定義，因此只能經過 PHP 的魔術方法 __get() 調用了。

咱們看看 Model 類的 __get() 方法：

/** * Dynamically retrieve attributes on the model. * * @param string $key * @return mixed */
public function __get($key) {
    return $this->getAttribute($key);
}
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好了，咱們開始解讀源代碼了：

/** * Get an attribute from the model. * * @param string $key * @return mixed */
public function getAttribute($key) {
    if (! $key) {
        return;
    }

    // If the attribute exists in the attribute array or has a "get" mutator we will
    // get the attribute's value. Otherwise, we will proceed as if the developers
    // are asking for a relationship's value. This covers both types of values.
    if (array_key_exists($key, $this->attributes) ||
        $this->hasGetMutator($key)) {
        return $this->getAttributeValue($key);
    }

    ...
}
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重點天然就在第二個 if 上，主要判斷 attributes 數組中是否包含該屬性，若是沒有，則會執行函數 $this->hasGetMutator($key)：

/** * Determine if a get mutator exists for an attribute. * * @param string $key * @return bool */
public function hasGetMutator($key) {
    return method_exists($this, 'get'.Str::studly($key).'Attribute');
}
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這就對上了咱們的 Demo 中自定義的函數 getAgeAttribute()，也就返回 true 了。

接下來就是執行函數 $this->getAttributeValue($key),進而執行函數：return $this->mutateAttribute($key, $value);

/** * Get the value of an attribute using its mutator. * * @param string $key * @param mixed $value * @return mixed */
protected function mutateAttribute($key, $value) {
    return $this->{'get'.Str::studly($key).'Attribute'}($value);
}
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好了，到此咱們基本就知道了獲取自定義 Attribute 的流程了。

相信解析 set XxxAttribute 也是很簡單的。

總結

好長時間沒寫東西了，先從最簡單的入手，練練手。解析 Eloquent 須要費不少腦細胞，接下來的一段時間我會圍繞着這個主題好好研究下去，儘量的所有解讀一遍：：

.
|____Capsule
| |____Manager.php
|____composer.json
|____Concerns
| |____BuildsQueries.php
| |____ManagesTransactions.php
|____Connection.php
|____ConnectionInterface.php
|____ConnectionResolver.php
|____ConnectionResolverInterface.php
|____Connectors
| |____ConnectionFactory.php
| |____Connector.php
| |____ConnectorInterface.php
| |____MySqlConnector.php
| |____PostgresConnector.php
| |____SQLiteConnector.php
| |____SqlServerConnector.php
|____Console
| |____Factories
| | |____FactoryMakeCommand.php
| | |____stubs
| | | |____factory.stub
| |____Migrations
| | |____BaseCommand.php
| | |____FreshCommand.php
| | |____InstallCommand.php
| | |____MigrateCommand.php
| | |____MigrateMakeCommand.php
| | |____RefreshCommand.php
| | |____ResetCommand.php
| | |____RollbackCommand.php
| | |____StatusCommand.php
| |____Seeds
| | |____SeedCommand.php
| | |____SeederMakeCommand.php
| | |____stubs
| | | |____seeder.stub
|____DatabaseManager.php
|____DatabaseServiceProvider.php
|____DetectsDeadlocks.php
|____DetectsLostConnections.php
|____Eloquent
| |____Builder.php
| |____Collection.php
| |____Concerns
| | |____GuardsAttributes.php
| | |____HasAttributes.php
| | |____HasEvents.php
| | |____HasGlobalScopes.php
| | |____HasRelationships.php
| | |____HasTimestamps.php
| | |____HidesAttributes.php
| | |____QueriesRelationships.php
| |____Factory.php
| |____FactoryBuilder.php
| |____JsonEncodingException.php
| |____MassAssignmentException.php
| |____Model.php
| |____ModelNotFoundException.php
| |____QueueEntityResolver.php
| |____RelationNotFoundException.php
| |____Relations
| | |____BelongsTo.php
| | |____BelongsToMany.php
| | |____Concerns
| | | |____InteractsWithPivotTable.php
| | | |____SupportsDefaultModels.php
| | |____HasMany.php
| | |____HasManyThrough.php
| | |____HasOne.php
| | |____HasOneOrMany.php
| | |____MorphMany.php
| | |____MorphOne.php
| | |____MorphOneOrMany.php
| | |____MorphPivot.php
| | |____MorphTo.php
| | |____MorphToMany.php
| | |____Pivot.php
| | |____Relation.php
| |____Scope.php
| |____SoftDeletes.php
| |____SoftDeletingScope.php
|____Events
| |____ConnectionEvent.php
| |____QueryExecuted.php
| |____StatementPrepared.php
| |____TransactionBeginning.php
| |____TransactionCommitted.php
| |____TransactionRolledBack.php
|____Grammar.php
|____Migrations
| |____DatabaseMigrationRepository.php
| |____Migration.php
| |____MigrationCreator.php
| |____MigrationRepositoryInterface.php
| |____Migrator.php
| |____stubs
| | |____blank.stub
| | |____create.stub
| | |____update.stub
|____MigrationServiceProvider.php
|____MySqlConnection.php
|____PostgresConnection.php
|____Query
| |____Builder.php
| |____Expression.php
| |____Grammars
| | |____Grammar.php
| | |____MySqlGrammar.php
| | |____PostgresGrammar.php
| | |____SQLiteGrammar.php
| | |____SqlServerGrammar.php
| |____JoinClause.php
| |____JsonExpression.php
| |____Processors
| | |____MySqlProcessor.php
| | |____PostgresProcessor.php
| | |____Processor.php
| | |____SQLiteProcessor.php
| | |____SqlServerProcessor.php
|____QueryException.php
|____README.md
|____Schema
| |____Blueprint.php
| |____Builder.php
| |____Grammars
| | |____ChangeColumn.php
| | |____Grammar.php
| | |____MySqlGrammar.php
| | |____PostgresGrammar.php
| | |____RenameColumn.php
| | |____SQLiteGrammar.php
| | |____SqlServerGrammar.php
| |____MySqlBuilder.php
| |____PostgresBuilder.php
| |____SQLiteBuilder.php
| |____SqlServerBuilder.php
|____Seeder.php
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參考

• Eloquent： 修改器 laravel-china.org/docs/larave…
• __get()使用說明 php.net/manual/zh/l…

未完待續