Laravel 5.8 如何设置默认值Laravel<；选择>；元素？

我想在类别名称中检索数据库值，并在选择中显示默认值。这是我的编辑视图的控制器

我有一个

category\u产品

表

Product.php

public function categories()
{
    return $this->belongsToMany(Category::class);
}

我得到这个错误

未定义的属性：Illumb\Database\Eloquent\Relations\BelongToMany:：$category\U id

---

您需要在

foreach（）

循环上方的select标记中添加默认值

<div class="col-md-4">
    <div class="form-group">
        <label for="category">category</label>
        <select class="form-control" name="category" id="category">
            <option value="xyz">xyz</option> /* set default option value */
            @foreach($categories as $category)
                <option value="{{ $category->id }}" {{$category->id == $category->id ? 'selected' : '' }}>{{ $category->name }}</option>
            @endforeach
        </select>
    </div>
</div>

---

我改变了密码，但我的问题还没有解决。

public function categories()
{
    return $this->belongsToMany(Category::class);
}

<div class="col-md-4">
    <div class="form-group">
        <label for="category">category</label>
        <select class="form-control" name="category" id="category">
            <option value="xyz">xyz</option> /* set default option value */
            @foreach($categories as $category)
                <option value="{{ $category->id }}" {{$category->id == $category->id ? 'selected' : '' }}>{{ $category->name }}</option>
            @endforeach
        </select>
    </div>
</div>

 <select class="form-control" name="category" id="category">

      @foreach($categories as $category)
           <option value="{{ $category->id }}" {{$product->catetory_id == $category->id ? 'selected' : '' }}>{{ $category->name }}</option>
      @endforeach
 </select>