laravel5 中 关联查询

有这么一组数据

一个学生表users 和 学生成绩表 grades 两个表关联

在方法里面是这样的

public function index()
{
    $result = User::where('is_admin', 0);
    $users = $result->get();
    $count = $result->count();       
    return view('admin.list', compact('count', 'users'));
}

视图循环是这样的

 @foreach ($users as $user)
    <tr>
        <td>{{$user->id}}</td>
        <td>{{$user->name}}</td>
        <td>{{$user->grade->math}}</td>
        <td>{{$user->grade->english}}</td>
        <td>{{$user->grade->c}}</td>
        <td>{{$user->grade->sport}}</td>
        <td>{{$user->grade->think}}</td>
        <td>{{$user->grade->soft}}</td>
    </tr>
@endforeach

得到的结果是 报错 Trying to get property of non-object (View:

$user->grade->math

是找不到的 怎么做关联一起呢

---

phpUser.php定义
public function Grade()
    {
        return $this->hasOne("App\Modules\Grade", 'user_id', 'id');
    }
controller.php
public function index()
{
    $result = User::where('is_admin', 0);
    $users = $result->grade()->get();
    $count = $result->count();       
    return view('admin.list', compact('count', 'users'));
}

view:
@foreach ($users as $user)
    <tr>
        <td>{{$user->id}}</td>
        <td>{{$user->name}}</td>
        <td>{{$user->math}}</td>
        <td>{{$user->english}}</td>
        <td>{{$user->c}}</td>
        <td>{{$user->sport}}</td>
        <td>{{$user->think}}</td>
        <td>{{$user->soft}}</td>
    </tr>
@endforeach

---

User.php

public function grade()
    {
        return $this->hasOne('App\Grade');
    }

Grade.php

public function user()
    {
        return $this->belongsTo('App\User');
    }