我有一个问题雄辩模型，课程雄辩模型，大学雄辩模型。大学与课程之间存在一对多的关系。问题与课程之间存在多对多的关系。三种模型如下所示：
问题模型
namespace App;
use Illuminate\Database\Eloquent\Model;
class Question extends Model
{
/**
* The database table that the Model uses
* @var string
*/
protected $table = "questions";
/**
* The fields that are mass assignable
* @var array
*/
protected $fillable = ['title','body','images','quality_score','deactivated','creator_id','reviewer_id'];
/**
* Images is stored as serialized json.
* So we cast it to a PHP array.
* See: http://laravel.com/docs/5.1/eloquent-mutators#attribute-casting
*/
protected $casts = [
'images' => 'array',
];
public function courses(){
return $this->belongsToMany('App\Course');
}
}
课程模型
namespace App;
use Illuminate\Database\Eloquent\Model;
class Course extends Model
{
/**
* The database table used by the model
* @var string
*/
protected $table = "courses";
/**
* The fields that can be mass assigned
* @var array
*/
protected $fillable = ['name', 'instructor', 'acronym', 'university_id', 'creator_id', 'reviewer_id'];
/**
* There exists a many to one relationship between the Course and User
* This user is the creator of the course
*
* @method void
*
*/
public function creator(){
return $this->hasOne('App\User','creator_id');
}
/**
* There exists a many to one relationship between the Course and User
* This user is the reviewer of the course
* The reviewer of the Course will always be an admin
* If an Admin is the creator, then the reviewer is also the same admin
*
* @method void
*/
public function reviewer(){
return $this->hasOne('App\User','reviewer_id');
}
/**
* There exists a one to many relationship between the University and the Course
* This university is where the course is held
* Courses may float i.e. not be associated to any university
*
* @method void
*/
public function university(){
return $this->belongsTo('App\University');
}
/**
* This method is an accessor. It automatically changes the acronym to be all capitals
* regardless of how it is stored in the database.
* See: http://laravel.com/docs/5.1/eloquent-mutators#accessors-and-mutators
* @param $value (String from Database)
* @return string (Capitalized String)
*/
public function getAcronymAttribute($value){
return strtoupper($value);
}
}
大学模式
namespace App;
use Illuminate\Database\Eloquent\Model;
class University extends Model
{
/**
* The database table used by the model
* @var string
*/
protected $table = "universities";
/**
* The fields that can be mass assigned
* name = Name of the University (Example: University of Illinois at Urbana Champaign)
* acronym = Acronym of the University (Example: UIUC)
* creator_id = Id of User that created the University
* reviewer_id = Id of User that reviewed and approved the University
*
* Universities will not be displayed to users without admin role unless they have been reviewed.
*
* @var array
*/
protected $fillable = ['name','acronym','creator_id','reviewer_id'];
/**
* This method is an accessor. It automatically changes the acronym to be all capitals
* regardless of how it is stored in the database.
* See: http://laravel.com/docs/5.1/eloquent-mutators#accessors-and-mutators
* @param $value (String from Database)
* @return string (Capitalized String)
*/
public function getAcronymAttribute($value){
return strtoupper($value);
}
}
在我的主页上，我显示了一系列问题，并允许过滤课程和大学。控制器方法如下所示：
public function getHome(Request $request){
/**
* Eager Load with Course and University
*/
$questions = Question::with('courses.university')->get();
/*
* Filter Questions to remove unwanted entries based on course id
*/
if($request->has('course_id') && $request->input('course_id') != -1){
$questions = $questions->filter(function($question) use ($request){
foreach($question->courses as $course){
if ($course->id == $request->input('course_id')){
return true;
}
}
});
}
/*
* Filter Questions to remove unwanted entries based on university id
*/
if($request->has('university_id') && $request->input('university_id') != -1){
$questions = $questions->filter(function($question) use ($request){
foreach($question->courses as $course){
if ($course->university->id == $request->input('university_id')){
return true;
}
}
});
}
/*
* Return the Welcome View with Pagination on the Questions Displayed
* List of Courses and List of Universities
*/
return view('welcome',[
'questions' => $questions,
'courses' => Course::all(),
'universities' => University::all(),
'selected_university_id' => $request->input('university_id',-1),
'selected_course_id' => $request->input('course_id',-1)
]);
}
我上面所做的是返回数据库中的所有问题，并将它们组合在一起以删除所有与过滤器不匹配的问题。这显然效率很低。我想使用带有约束的嵌套Eager Loading，除了我在定义约束的外观方面遇到很多麻烦。此外，我想使用服务器端分页来使客户端在低速互联网连接上体验更好。
以下是我的一次尝试：
$questions = Question::with(['courses.university' => function($query) use ($request){
if($request->has('university_id') && $request->input('university_id') != -1) {
$query->where('id', $request->input('university_id'));
}
if($request->has('course_id') && $request->input('course_id') != -1){
$query->where('courses.id',$request->input('course_id'));
}
}])->paginate(10);
当我没有任何过滤器时，此功能正常。
当我确定了一个university_id时，我收到错误：试图获取非对象的属性（查看：/var/www/testing.com/resources/views/welcome.blade.php）
当我确定了course_id时，我收到错误：SQLSTATE [42S22]：找不到列：1054未知列＆＃39; courses.id＆＃39;在＆＃39; where子句＆＃39; （SQL：从universities中选择*，其中universities。id位于（1,2）和courses。id = 1）
当我定义了course_id时，我预料到错误（因为我对$ query-＆gt; where方法的第一个参数进行了盲目的攻击。</ p>
我正在寻找帮助来定义嵌套的Eager Loading Constraints。
答案 0 :(得分：0)
我在一篇中篇文章中找到了解决方案。该解决方案适用于laravel的更高版本，因为它使用 whereHas 。
// If you want to put the constraint on the second relation
$questions = Question::with(['courses' => function($query) use($request){
return $query->whereHas('university', function($inner_query) use($request){
return $inner_query->where('id', $request->input('university_id'));
});
}, 'courses.university'])->paginate(10);
对于您的情况，一个简单的方法就可以解决问题。
$questions = Question::whereHas('courses', function($query) use ($request){
return $query->where('university_id', $request->input('university_id'));
})->with(['courses.university'])->paginate(10);
我还建议使用when子句以减少代码量。
$questions = Question::when(($request->has('course_id') && $request->input('course_id') != -1), function ($query) use($request){
return $query->where('course_id', $request->input('course_id'));
})->when($request->has('university_id') && $request->input('university_id') != -1, function ($outer_query) use($request){
return $outer_query->whereHas('courses', function($query) use($request){
return $query->where('university_id', $request->input('university_id'));
})->with(['courses.university']);
})->with(['courses.university'])->paginate(10);