Laravel 如何使用可选关系实现hasOne

我有一张这样的顾客桌

id
name

像这样的另一个表策略

id
policy_name

id 
customer_id
policy_id

    protected $appends = ['policy_customer'];

    public function policy_customer() {
        return $this->hasOne('App\Models\PolicyCustomer', "customer_id", "id");
    }

    public function getPolicyCustomerAttribute(){
        return $this->policy_customer()->firstOrFail();
    }

还有另一位像这样的顾客

id
policy_name

id 
customer_id
policy_id

    protected $appends = ['policy_customer'];

    public function policy_customer() {
        return $this->hasOne('App\Models\PolicyCustomer', "customer_id", "id");
    }

    public function getPolicyCustomerAttribute(){
        return $this->policy_customer()->firstOrFail();
    }

在我的客户模型中，我是这样写的

id
policy_name

id 
customer_id
policy_id

    protected $appends = ['policy_customer'];

    public function policy_customer() {
        return $this->hasOne('App\Models\PolicyCustomer', "customer_id", "id");
    }

    public function getPolicyCustomerAttribute(){
        return $this->policy_customer()->firstOrFail();
    }

在客户模型中

    public function policy() {
        return $this->belongsTo('App\Models\Policy', "policy_id", "id");
    }

    public function customer() {
        return $this->belongsTo('App\Models\Customer', "customer_id", "id");
    }

并非所有客户都有与其帐户关联的策略。 当我查询Customer:：get（）时，没有问题。但是，如果我尝试将其作为控制器的响应返回，我会得到如下错误：

[2020-02-06 06:11:47] local.ERROR: Illuminate\Database\Eloquent\ModelNotFoundException: No query results for model [App\Models\PolicyCustomer]. in D:\Projects\others\jayhawker\backend\vendor\laravel\framework\src\Illuminate\Database\Eloquent\Builder.php:454
Stack trace:
#0 D:\Projects\others\jayhawker\backend\vendor\laravel\framework\src\Illuminate\Support\Traits\ForwardsCalls.php(23): Illuminate\Database\Eloquent\Builder->firstOrFail()
#1 D:\Projects\others\jayhawker\backend\vendor\laravel\framework\src\Illuminate\Database\Eloquent\Relations\Relation.php(385): Illuminate\Database\Eloquent\Relations\Relation->forwardCallTo(Object(Illuminate\Database\Eloquent\Builder), 'firstOrFail', Array)
#2 D:\Projects\others\jayhawker\backend\app\Models\Customer.php(41): Illuminate\Database\Eloquent\Relations\Relation->__call('firstOrFail', Array)
#3 D:\Projects\others\jayhawker\backend\vendor\laravel\framework\src\Illuminate\Database\Eloquent\Concerns\HasAttributes.php(454): App\Models\Customer->getPolicyAttribute(NULL)
#

如果我从客户模型中删除getPolicyCustomerAttribute函数，它不会引发异常。

---

我遗漏了什么吗？

只需删除您的

getPolicyCustomerAttribute

访问器方法。所有关系方法都会自动提供包含关系结果的同名属性

也就是说，

$customer->policy\u customer

将包含相关的PolicyCustomer实例，或者如果没有相关记录，它将为

null

$customer->policy_customer === $customer->policy_customer()->first();

---

您的数据库看起来像

多对多

。策略和客户之间的关系是什么？您可以使用

多对多

关系。我也尝试了多对多。如果我删除getPolicyCustomerAttribute，错误将消失，但对象不在结果json中