php - 查询生成器上的未定义关系方法 - Laravel

Question

我有 3 个表users、teams、athletes。

用户可以是团队或运动员。

我将 user_id 放入 teams 和 athletes 表中。

我将下面的代码放在 User.php 模型中。

public function team()
{
    return $this->hasOne (Team::class);
}


public function athlete()
{
    return $this->hasOne (Athlete::class);
}

我把下面的代码放在 Team.php 模型中

public function user()
{
    return $this->belongsTo(User::class);
}

我把下面的代码放在 Athlete.php

public function user()
{
    return $this->belongsTo(User::class);
}

我在 Controller 中使用以下代码。

$staff_picks = User::notAdmin()->active()->orderBy('id','desc')->take(10)->team()->athlete()->get();

我遇到了错误

laravel.ERROR: Call to undefined method Illuminate\Database\Eloquent\Builder::team()`

知道为什么会这样吗？

Answer 1

好的，所以错误说

Call to undefined method Illuminate\Database\Eloquent\Builder::team()

这意味着 team() 方法未在类 Builder 中定义

现在 Builder 类位于vendor/laravel/framework/src/Illuminate/Database/Eloquent/Builder.php 命名空间Illuminate\Database\Eloquent下

从逻辑上讲，名为 team() 的函数不可能存在，对吧？

---

什么是team()？那么我该如何调用它呢？

team() 是模型 app/User.php 中的一个函数，它返回一个 hasOne 函数

好的，hasOne() 在哪里？

hasOne 是在 vendor/laravel/framework/src/Illuminate/Database/Eloquent/Concerns/HasRelationships.php 命名空间 Illuminate\Database 下的特征\Eloquent\Concerns

See here

namespace Illuminate\Database\Eloquent\Concerns;
// Imports ommitted for brevity

trait HasRelationships
{
// Other methods ommitted for brevity

/**
 * Define a one-to-one relationship.
 *
 * @param  string  $related
 * @param  string  $foreignKey
 * @param  string  $localKey
 * @return \Illuminate\Database\Eloquent\Relations\HasOne
 */
public function hasOne($related, $foreignKey = null, $localKey = null)
{
    $instance = $this->newRelatedInstance($related);
    $foreignKey = $foreignKey ?: $this->getForeignKey();
    $localKey = $localKey ?: $this->getKeyName();
    return $this->newHasOne($instance->newQuery(), $this, $instance->getTable() . '.' . $foreignKey, $localKey);
}
// Other methods are omitted for brevity

但是它怎么称呼呢？我没有使用 HasRelationships 特征

没错，app/User.php 类没有使用 HasRelationships 特性，但它扩展了一个使用该特性的类*

use Illuminate\Foundation\Auth\User as Authenticatable;

class User extends Authenticatable

*虽然不是直接的

Illuminate\Foundation\Auth\User extends Illuminate\Database\Eloquent\Model

See Here

namespace Illuminate\Foundation\Auth;

// Other Imports ommitted for brevity
use Illuminate\Database\Eloquent\Model;

class User extends Model implements
    AuthenticatableContract,
    AuthorizableContract,
    CanResetPasswordContract
{
    use Authenticatable, Authorizable, CanResetPassword, MustVerifyEmail;
}

和

Illuminate\Database\Eloquent\Model uses the Concerns\HasRelationships trait

See Here

namespace Illuminate\Database\Eloquent;

// Imports ommitted for brevity

abstract class Model implements Arrayable, ArrayAccess, Jsonable, JsonSerializable, QueueableEntity, UrlRoutable
{
    use Concerns\HasAttributes,
        Concerns\HasEvents,
        Concerns\HasGlobalScopes,
        Concerns\HasRelationships, // <-- THERE IT IS HERE!!!!
        Concerns\HasTimestamps,
        Concerns\HidesAttributes,
        Concerns\GuardsAttributes,
        ForwardsCalls;
// Rest of class ommitted for brevity

等等!这个类如何知道特征 Concerns\HasRelationships 在没有导入的情况下来自哪里？

因为 Concerns 是附加(或嵌套)到同一命名空间的命名空间，所以此类定义于

这个类在 Illuminate\Database\Eloquent 和 HasRelationships 是在 Illuminate\Database\Eloquent\Concerns 所以一个简单的调用 Concerns\HasRelationships 就足够了

现在 HasRelationships trait 中有函数 hasOne

好的，那么如何避免这个错误呢？

确保您是从模型实例而不是查询生成器调用模型中定义的关系

例子

错

User::where('name', 'John Doe')->teams;

正确

User::where('name', 'John Does')->first()->teams;

但为什么呢？

在检索该模型之前，您对该模型所做的任何 SQL 操作都是一个查询生成器实例

但是一旦你通过 first() 获得模型本身，你就可以调用关系

更新:回答问题的具体场景

您可能想要获取多个模型，因此在获取每条记录之后调用关系函数 team() 并不理想

解决方案？

预加载

使用 with 方法将关系数据包含在通过 get() 获取的集合中

示例

假设我有一个 User 和一个 Profile

每个用户都有一个且只有一个配置文件，所以我在 User 模型上定义了一个 hasOne 关系

public function profile()
{
    return $this->hasOne(Profile::class);
}

现在我们在迁移中需要一个外键来将profiles 表与users 表相关联

Schema::create('profiles', function (Blueprint $table) {
    $table->bigIncrements('id');
    $table->integer('age'); // Column to test with
    $table->unsignedBigInteger('user_id');
    $table->foreign('user_id')->references('id')->on('users');
    $table->timestamps();
});

现在让我们播种一些数据

public function run()
{
    factory(User::class, 10)->create()->each(function ($user) {
        $user->profile()->create(['age' => rand(20, 60)]);
    });
}

现在让我们打开 artisan tinker 看看会发生什么

>>> App\User::take(10);
=> Illuminate\Database\Eloquent\Builder {#3067}

take() User 模型上的函数返回一个 Builder 实例

让我们尝试获取关于它的配置文件

>>> App\User::take(10)->profile();

错误

BadMethodCallException with message 'Call to undefined method Illuminate/Database/Eloquent/Builder::profile()'

但现在我们知道为什么了

现在让我们试试预加载

>>> App\User::take(10)->with('profile');
=> Illuminate\Database\Eloquent\Builder {#3056}

返回一个查询生成器

让我们调用 get()

>>> App\User::take(10)->with('profile')->get();

现在我们得到了我们的数据集合

=> Illuminate\Database\Eloquent\Collection {#3070
     all: [
       App\User {#3022
         id: 1,
         name: "Augusta Botsford MD",
         email: "xwaelchi@example.net",
         email_verified_at: "2019-09-30 16:40:12",
         created_at: "2019-09-30 16:40:12",
         updated_at: "2019-09-30 16:40:12",
         profile: App\Profile {#3095
           id: 1,
           age: 29,
           user_id: 1,
           created_at: "2019-09-30 16:40:12",
           updated_at: "2019-09-30 16:40:12",
         },
       },
       App\User {#3017
         id: 2,
         name: "Olga Leannon",
         email: "ufay@example.com",
         email_verified_at: "2019-09-30 16:40:12",
         created_at: "2019-09-30 16:40:12",
         updated_at: "2019-09-30 16:40:12",
         profile: App\Profile {#3096
           id: 2,
           age: 24,
           user_id: 2,
           created_at: "2019-09-30 16:40:12",
           updated_at: "2019-09-30 16:40:12",
         },
       },
       App\User {#3019
         id: 3,
         name: "Bria Prosacco DDS",
         email: "hartmann.trystan@example.com",
         email_verified_at: "2019-09-30 16:40:12",
         created_at: "2019-09-30 16:40:12",
         updated_at: "2019-09-30 16:40:12",
         profile: App\Profile {#3097
           id: 3,
           age: 43,
           user_id: 3,
           created_at: "2019-09-30 16:40:12",
           updated_at: "2019-09-30 16:40:12",
         },
       },
       App\User {#3054
         id: 4,
         name: "Clare Bayer",
         email: "rosalinda60@example.org",
         email_verified_at: "2019-09-30 16:40:12",
         created_at: "2019-09-30 16:40:12",
         updated_at: "2019-09-30 16:40:12",
         profile: App\Profile {#3098
           id: 4,
           age: 52,
           user_id: 4,
           created_at: "2019-09-30 16:40:12",
           updated_at: "2019-09-30 16:40:12",
         },
       },
       App\User {#3058
         id: 5,
         name: "Vickie Kub",
         email: "katherine.abbott@example.com",
         email_verified_at: "2019-09-30 16:40:12",
         created_at: "2019-09-30 16:40:12",
         updated_at: "2019-09-30 16:40:12",
         profile: App\Profile {#3099
           id: 5,
           age: 42,
           user_id: 5,
           created_at: "2019-09-30 16:40:12",
           updated_at: "2019-09-30 16:40:12",
         },
       },
       App\User {#3059
         id: 6,
         name: "Tressie Gottlieb",
         email: "elmira.osinski@example.net",
         email_verified_at: "2019-09-30 16:40:12",
         created_at: "2019-09-30 16:40:12",
         updated_at: "2019-09-30 16:40:12",
         profile: App\Profile {#3100
           id: 6,
           age: 21,
           user_id: 6,
           created_at: "2019-09-30 16:40:12",
           updated_at: "2019-09-30 16:40:12",
         },
       },
       App\User {#3042
         id: 7,
         name: "Saige Pollich",
         email: "gkemmer@example.org",
         email_verified_at: "2019-09-30 16:40:12",
         created_at: "2019-09-30 16:40:12",
         updated_at: "2019-09-30 16:40:12",
         profile: App\Profile {#3101
           id: 7,
           age: 24,
           user_id: 7,
           created_at: "2019-09-30 16:40:12",
           updated_at: "2019-09-30 16:40:12",
         },
       },
       App\User {#3087
         id: 8,
         name: "Dr. Emiliano Sauer",
         email: "marks.florida@example.net",
         email_verified_at: "2019-09-30 16:40:12",
         created_at: "2019-09-30 16:40:12",
         updated_at: "2019-09-30 16:40:12",
         profile: App\Profile {#3102
           id: 8,
           age: 42,
           user_id: 8,
           created_at: "2019-09-30 16:40:12",
           updated_at: "2019-09-30 16:40:12",
         },
       },
       App\User {#3086
         id: 9,
         name: "Genoveva Abshire",
         email: "colt.harber@example.com",
         email_verified_at: "2019-09-30 16:40:12",
         created_at: "2019-09-30 16:40:12",
         updated_at: "2019-09-30 16:40:12",
         profile: App\Profile {#3103
           id: 9,
           age: 27,
           user_id: 9,
           created_at: "2019-09-30 16:40:12",
           updated_at: "2019-09-30 16:40:12",
         },
       },
       App\User {#3088
         id: 10,
         name: "Dimitri Moore",
         email: "slockman@example.net",
         email_verified_at: "2019-09-30 16:40:12",
         created_at: "2019-09-30 16:40:12",
         updated_at: "2019-09-30 16:40:12",
         profile: App\Profile {#3104
           id: 10,
           age: 30,
           user_id: 10,
           created_at: "2019-09-30 16:40:12",
           updated_at: "2019-09-30 16:40:12",
         },
       },
     ],
   }

我希望这能消除一些困惑