Laravel5.8 belongsTo 关系不适用于 foreach 循环

Question

我正在使用 hasMany 和 belongsTo 处理 Laravel 关系。它适用于 hasMany 关系，但我在 belongsTo for collection foreach 循环中遇到问题。这是我的 categories table.

    id    name
  --------------
    1     food

和products table.

    id    name         category_id
  ----------------------------------
    1     pizza          1
    2     hamburger      1

以下是hasMany产品型号。

# Product.php

public function products()
{
    return $this->hasMany(Product::class);
}

下面是belongsTo类目模型。

# Category.php

public function category()
{
    return $this->belongsTo(Category::class, 'id');
}

我在 blade 中遇到错误：

Trying to get property of non-object

 <tbody>
   @foreach ($products as $product)
      <tr>
           <td> {{ $product->category->name }} </td>
       </tr>
    @endforeach
  </tbody>

如有任何建议或指导，我们将不胜感激，谢谢

Answer 1

问题出在方法定义上。 belongsTo 方法的第二个参数是外键列名。试试这个：

# Product.php

public function category()
{
    return $this->belongsTo(Category::class, 'category_id');
}

但是，鉴于您的外键是型号名称后跟 _id (category_id)，Laravel 默认会查找此键..所以您可以简化它像这样：

# Product.php

public function category()
{
    return $this->belongsTo(Category::class);
}

来自documentation：

... In the example above, Eloquent will try to match the post_id from the Comment model to an id on the Post model. Eloquent determines the default foreign key name by examining the name of the relationship method and suffixing the method name with a _ followed by the name of the primary key column. However, if the foreign key on the Comment model is not post_id, you may pass a custom key name as the second argument to the belongsTo method:
/**
 * Get the post that owns the comment.
 */
public function post()
{
    return $this->belongsTo('App\Post', 'foreign_key');
}

Answer 2

Category.php

public function category()
{
  return $this->belongsTo(Category::class, 'category_id');
}

而不是 'id' in category() 使用 'category_id'..... 因为你已经给 category_id 作为外键....所以 laravel 会搜索它...

Laravel5.8 belongsTo 关系不适用于 foreach 循环

Laravel5.8 belongsTo relation not working for foreach loop

php

laravel

laravel-5

relationship

belongs-to

Category.php