Laravel 5.4一对多关系（检查数据透视表中是否存在记录）

问题描述：

I want to check if current user already has this car.

User.php:

public function car()
    {
        return $this->hasMany(Car::class);
    }

Car.php

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

For example, I'm passing to view all cars from cars table and I want to check if current user already has this car:

@foreach( $cars as $car )

   @if(Auth::user()->cars->where('car_id', $car->id)->exists())

        You have this car!

   @else

        Buy this car!

   @endif

@endforeach

Now, this code returns an error:

Call to a member function where() on null

How can I check if User already has this car?

我想检查当前用户是否已经拥有此车。 p>

User.php： strong> p>

  public function car（）
 {
返回$ this-＆gt; hasMany（Car :: class）; 
  } 
  code>  pre> 
 
   Car.php  strong>  p> 
 
 
  public function user（）
 {  
返回$ this-＆gt; belongsTo（User :: class）; 
} 
  code>  pre> 
 
 例如，我要传递查看汽车表中的所有汽车 我想检查当前用户是否已经拥有这款车： p> 
 
 
  @foreach（$ cars as $ car）
 
 @if（Auth :: user（） -  ＆gt; cars-＆gt; where（'car_id'，$ car-＆gt; id） - ＆gt; exists（））
 
你有这辆车！
 
 @else 
 
购买这款车！  n 
 @endif 
 
 @ endforeach 
  code>  pre> 
 
 现在，此代码返回错误： p> 
 
 
 
 调用成员函数where（）on null  p> 
  blockquote> 
 
 如何检查用户是否已经拥有此车？ p> 
  div>

答

2 Problems:

First the typo car/cars.

Second, you have public function car() so it should be Auth::user()->car()->where('car_id', $car->id)->exists() for condition chaining.

Check out the "One To Many" Section in Laravel 5.4 Documentation about chaining query conditions (pretty much at the end of the section).

Laravel 5.4一对多关系（检查数据透视表中是否存在记录）

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