Laravel5 软删除（SoftDeletes）的 deleted_at 改造

正常来说数据库最好不要做真正的硬删除操作，所以可以改用柔和的软删除。也就是在数据库增加一个字段，比如 is_deleted，如果是 0 的时候表示正常，1 表示已被删除。

使用软删除可能碰到的问题：如果表中有 UNIQUE 索引的字段，比如 User 表的 username，被软删除后，username 已经被占用了，新的数据不能使用该 username。解决方法是，定义联合索引唯一约束，即 UNIQUE KEY username_INDEX (username) 改成 UNIQUE KEY username_INDEX (username, is_deleted)。

看上去问题好像解决了，但是新的问题：如果 username 被第二次软删除，is_deleted 为 1 的也被占用了。进一步的解决方法是把 is_deleted 定义为，当 0 值时表示未删除，非 0 表示被删除并且是一个自增 ID 或者时间戳或者 UUID，那么就能保证唯一性。

Laravel 框架已经提供了很好的软删除功能：《Soft Deleting》

To enable soft deletes for a model, use the Illuminate\Database\Eloquent\SoftDeletes trait on the model and add the deleted_at column to your $dates property:

使用步骤

1. 在表中增加字段 deleted_at
2. 在 Model 中使用 trait SoftDeletes
3. 在 Model 中添加 deleted_at 到 $dates 成员变量

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;

class Flight extends Model
{
    use SoftDeletes;

    /**
     * The attributes that should be mutated to dates.
     *
     * @var array
     */
    protected $dates = ['deleted_at'];
}

Laravel 的软删除就是用 delete_at 字段作为删除的标记，类型是 Timestamp，默认是 NULL 的话表示未删除。

但是，使用 Laravel 自带的软删除是存在文章开头提到的问题的。因为虽然可以定义联合唯一索引 UNIQUE：(username, deleted_at)，但是 deleted_at 默认值是 NULL，MySQL 下唯一值是不算 NULL 的，即唯一值列出现多个 NULL 值都不会报错。

我的改进方法是把 deleted_at 改成存储 BIGINT 类型的 Unix 时间戳，默认值 0。

SoftDeletes：app/Models/SoftDeletesEx.php

<?php
namespace App\Models;

use Illuminate\Database\Eloquent\SoftDeletes;

trait SoftDeletesEx {
    use SoftDeletes;

    /**
     * Boot the soft deleting trait for a model.
     *
     * @return void
     */
    public static function bootSoftDeletes() {
        static::addGlobalScope(new SoftDeletingScopeEx());
    }

    /**
     * Perform the actual delete query on this model instance.
     *
     * @return void
     */
    protected function runSoftDelete() {
        $query = $this->newQueryWithoutScopes()->where($this->getKeyName(), $this->getKey());
        
        $this->{$this->getDeletedAtColumn()} = $time = \DB::Raw('UNIX_TIMESTAMP(NOW())');
        
        $query->update([
            $this->getDeletedAtColumn() => $time
        ]);
    }

    /**
     * Restore a soft-deleted model instance.
     *
     * @return bool|null
     */
    public function restore() {
        // If the restoring event does not return false, we will proceed with this
        // restore operation. Otherwise, we bail out so the developer will stop
        // the restore totally. We will clear the deleted timestamp and save.
        if ($this->fireModelEvent('restoring') === false) {
            return false;
        }
        
        $this->{$this->getDeletedAtColumn()} = 0;
        
        // Once we have saved the model, we will fire the "restored" event so this
        // developer will do anything they need to after a restore operation is
        // totally finished. Then we will return the result of the save call.
        $this->exists = true;
        
        $result = $this->save();
        
        $this->fireModelEvent('restored', false);
        
        return $result;
    }

    /**
     * Determine if the model instance has been soft-deleted.
     *
     * @return bool
     */
    public function trashed() {
        return ! ($this->{$this->getDeletedAtColumn()} === 0);
    }
}

app/Models/SoftDeletingScopeEx.php

<?php
namespace App\Models;

use Illuminate\Database\Eloquent\Builder;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletingScope;

class SoftDeletingScopeEx extends SoftDeletingScope {

    /**
     * Apply the scope to a given Eloquent query builder.
     *
     * @param \Illuminate\Database\Eloquent\Builder $builder            
     * @param \Illuminate\Database\Eloquent\Model $model            
     * @return void
     */
    public function apply(Builder $builder, Model $model) {
        $builder->where($model->getQualifiedDeletedAtColumn(), 0);
    }

    /**
     * Extend the query builder with the needed functions.
     *
     * @param \Illuminate\Database\Eloquent\Builder $builder            
     * @return void
     */
    public function extend(Builder $builder) {
        foreach ($this->extensions as $extension) {
            $this->{"add{$extension}"}($builder);
        }
        
        $builder->onDelete(function (Builder $builder) {
            $column = $this->getDeletedAtColumn($builder);
            
            return $builder->update([
                $column => \DB::Raw('UNIX_TIMESTAMP(NOW())')
            ]);
        });
    }

    /**
     * Add the restore extension to the builder.
     *
     * @param \Illuminate\Database\Eloquent\Builder $builder            
     * @return void
     */
    protected function addRestore(Builder $builder) {
        $builder->macro('restore', function (Builder $builder) {
            $builder->withTrashed();
            
            return $builder->update([
                $builder->getModel()
                    ->getDeletedAtColumn() => 0
            ]);
        });
    }

    /**
     * Add the without-trashed extension to the builder.
     *
     * @param \Illuminate\Database\Eloquent\Builder $builder            
     * @return void
     */
    protected function addWithoutTrashed(Builder $builder) {
        $builder->macro('withoutTrashed', function (Builder $builder) {
            $model = $builder->getModel();
            
            $builder->withoutGlobalScope($this)
                ->where($model->getQualifiedDeletedAtColumn(), 0);
            
            return $builder;
        });
    }

    /**
     * Add the only-trashed extension to the builder.
     *
     * @param \Illuminate\Database\Eloquent\Builder $builder            
     * @return void
     */
    protected function addOnlyTrashed(Builder $builder) {
        $builder->macro('onlyTrashed', function (Builder $builder) {
            $model = $builder->getModel();
            
            $builder->withoutGlobalScope($this)
                ->where($model->getQualifiedDeletedAtColumn(), '<>', 0);
            
            return $builder;
        });
    }
}

我把代码放在 GitHub：https://github.com/broly8/SoftDeletesEx