感觉好长时间没写东西了，一方面主要是自己的角色发生了变化，每天要面对各种各样的事情和突发事件，不能再有一个完整的长时间让自己静下来写代码，或者写文章。

另一方面现在公司技术栈不再停留在只有 Laravel + VUE 了，我们还有小程序、APP 等开发，所以我关注的东西也就多了。

接下来我还是会继续持续「高产」，把写技术文章当作一个习惯，坚持下去。

好了，废话不多说，今天来说一说「Eloquent： 修改器」。

一直想好好研究下 Eloquent。但苦于 Eloquent 有太多可研究的，无法找到一个切入点。前两天看一同事好像对这个「Eloquent： 修改器」了解不多，所以今天就拿它作为入口，扒一扒其实现源代码。

首先还是拿一个 Demo 为例：

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);
    }
}

这个代码比较简单，就是通过已有属性 birthday，计算 Baby 几岁了，得到 age 属性。

前端就可以直接拿到结果：

return $baby->age;

同样的，还有 setXxxAttribute 方法来定义一个修改器。

源代码

读代码还是从使用入手，如上通过 $baby->age 调用 age 属性，这个属性没在类中定义，所以只能通过 PHP 的魔术方法 __get() 调用了。

我们看看 Model 类的 __get() 方法：

/**
 * Dynamically retrieve attributes on the model.
 *
 * @param  string  $key
 * @return mixed
 */
public function __get($key)
{
    return $this->getAttribute($key);
}

好了，我们开始解读源代码了：

/**
 * 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);
    }

    ...
}

重点自然就在第二个 if 上，主要判断 attributes 数组中是否包含该属性，如果没有，则会执行函数 $this->hasGetMutator($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');
}

这就对上了我们的 Demo 中自定义的函数 getAgeAttribute()，也就返回 true 了。

接下来就是执行函数 $this->getAttributeValue($key),进而执行函数：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);
}

好了，到此我们基本就知道了获取自定义 Attribute 的流程了。

相信解析 set XxxAttribute 也是很简单的。

总结

好长时间没写东西了，先从最简单的入手，练练手。解析 Eloquent 需要费很多脑细胞，接下来的一段时间我会围绕着这个主题好好研究下去，尽可能的全部解读一遍：：

.
|____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

参考

• Eloquent： 修改器 https://laravel-china.org/docs/laravel/5.7/eloquent-mutators/2297
• __get()使用说明 http://php.net/manual/zh/language.oop5.overloading.php#object.get

未完待续