SQLSTATE [42000]：语法错误或访问冲突：1066 Not unique table/alias on relationship

Question

所以，我从 Laravel 框架收到以下错误；但我找不到这个框架为什么会产生这个错误：

SQLSTATE[42000]: Syntax error or access violation: 1066 Not unique table/alias: 'participants' (SQL: select `participants`.*, `participants`.`message_id` as `pivot_message_id`, `participants`.`user_id` as `pivot_user_id`, `participants`.`created_at` as `pivot_created_at`, `participants`.`updated_at` as `pivot_updated_at` from `participants` inner join `participants` on `participants`.`id` = `participants`.`user_id` where `participants`.`deleted_at` is null and `participants`.`message_id` in (2))

我的消息/参与者关系如下所示：

public function participants()
{
    return $this->belongsToMany('Namespace\Modules\Email\Models\Participant', 'participants', 'message_id', 'user_id')->withTimestamps();
}

我试着这样称呼它：

public function getAllMessages()
{
   return Message::with('user')->with('participants')->get();
}

为什么会出现此错误？这是怎么回事？

编辑：包括完整模型

留言

class Message extends Eloquent
{
    use PublishedTrait;
    use SoftDeletingTrait;

    /**
     * The database table used by the model.
     *
     * @var string
     */
    protected $table = 'messages';

    /**
     * The attributes that can be set with Mass Assignment.
     *
     * @var array
     */
    protected $fillable = ['subject', 'user_id', 'body', 'status'];

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

    /**
     * Validation rules.
     *
     * @var array
     */
    protected $rules = [
        'subject' => 'required|max:255',
        'body' => 'required',
    ];

    /**
     * User relationship
     *
     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
     */
    public function user()
    {
        return $this->belongsTo(Config::get('email.user_model'));
    }

    public function assets()
    {
        return $this->belongsToMany('Namespace\Modules\Assets\Models\Asset', 'message_assets');
    }

    /**
     * Participants relationship
     *
     * @return \Illuminate\Database\Eloquent\Relations\HasMany
     */
    public function participants()
    {
        return $this->belongsToMany('Namespace\Modules\Email\Models\Participant', 'participants', 'message_id', 'user_id')->withTimestamps();
    }

    /**
     * Recipients of this message
     *
     * @return \Illuminate\Database\Eloquent\Relations\HasMany
     */
    public function recipients()
    {
        return $this->participants()->where('user_id', '!=', $this->user_id);
    }

    /**
     * Returns the latest message from a thread
     *
     * @return Namespace\Modules\Email\Models\Message
     */
    public function getLatestMessageAttribute()
    {
        return $this->messages()->latest()->first();
    }

    /**
     * Returns threads that the user is associated with
     * @param $query
     * @param $userId
     * @return mixed
     */
    public function scopeForUser($query, $userId)
    {
        return $query->join('participants', 'messages.id', '=', 'participants.message_id')
            ->where('participants.user_id', $userId)
            ->where('participants.deleted_at', null)
            ->select('messages.*');
    }

    /**
     * Returns threads that the user is associated with
     * @param $query
     * @param $userId
     * @return mixed
     */
    public function scopeForUserWithDeleted($query, $userId)
    {
        return $query->join('participants', 'messages.id', '=', 'participants.message_id')
            ->where('participants.user_id', $userId)
            ->select('messages.*');
    }

    /**
     * Returns messages that the user has sent
     * @param $query
     * @param $userId
     * @return mixed
     */
    public function scopeByUser($query, $userId)
    {
        return $query->where('user_id', $userId);
    }

    /**
     * Returns threads with new messages that the user is associated with
     * @param $query
     * @param $userId
     * @return mixed
     */
    public function scopeForUserWithNewMessages($query, $userId)
    {
        return $query->join('participants', 'messages.id', '=', 'participants.message_id')
            ->where('participants.user_id', $userId)
            ->whereNull('participants.deleted_at')
            ->where(function ($query) {
                $query->where('messages.updated_at', '>', $this->getConnection()->raw($this->getConnection()->getTablePrefix() . 'participants.last_read'))
                    ->orWhereNull('participants.last_read');
            })
            ->select('messages.*');
    }

}

参与者

class Participant extends Eloquent
{
    use SoftDeletingTrait;

    /**
     * The database table used by the model.
     *
     * @var string
     */
    protected $table = 'participants';

    /**
     * The attributes that can be set with Mass Assignment.
     *
     * @var array
     */
    protected $fillable = ['message_id', 'user_id', 'last_read'];

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

    /**
     * Thread relationship
     *
     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
     */
    public function message()
    {
        return $this->hasMany('Namespace\Modules\Email\Models\Message');
    }

    /**
     * User relationship
     *
     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
     */
    public function user()
    {
        return $this->belongsTo(Config::get('email.user_model'));
    }
}

Answer 1

为很久以后遇到此错误的任何人回答此问题。

从您的表记录来看，participants table 似乎是users 和messages 之间的pivot table。您正在引用数据透视表，导致数据库行为不端。

执行此操作的正确方法是在您的 users 模型中：

public function messages(){
   return $this->belongsToMany(Message::class, 'participants', 'user_id', 'message_id')->withPivot('last_read');
}

在您的messages 模型中：

public function users(){
   return $this->belongsToMany(User::class, 'participants', 'message_id', 'user_id')->withPivot('last_read');
}

这样，当你调用来自用户的消息时，使用这个：

$messages = $user->messages()->get();

当你检查用户的消息时，

$user = $message->users()->get()

最后一次阅读

$last_read = $message->pivot->last_read;

Answer 2

通过 Larachat 官方 Slack 回答：

此关系缺少数据透视表才能正常工作。 participants 方法中的第二个参数是要使用的数据透视表：

public function participants()
{
    return $this->belongsToMany('Namespace\Modules\Email\Models\Participant', 'PIVOT', 'message_id', 'user_id')->withTimestamps();
}

因此，您不能使用参与者作为数据透视表，因为它是关系中的表之一，您需要一个message_participant 数据透视表。

Answer 3

你的错误是

...from `participants` inner join `participants` ...

您需要为每个引用提供别名，如

...from `participants` p1 inner join `participants` p2 ...

然后在正确的地方使用p1和p2，例如

...on p1.`id` = p2.`user_id` ...

（我猜哪个是p1，哪个是p2；你必须做出决定）