如何通过 Eloquent 获取单个集合中每位教师的学生数

Question

A Teacher has many Students. When I am showing the Teachers list I also want to show the counts of Student for each Teachers. How can I do this by using Eloquent?

I can find the Teachers from this, $teacher= Teacher::where('teacher_status','active')->get();

I can find the Student count from this $student_count = Student::where('teacher_id','teachers.id')->count();

How can I conbine this two query and return the response in a single array/collection?

Answer 1

If you want to count the number of students related to teacher without actually loading them you may use the withCount method and this add new propery named by a {relation}_count column on your resulting models. For example:

Teacher::where('teacher_status','active')->withCount('students')->get();

Also you need and to your Teacher model hasMany relation method to Students

Answer 2

In your teacher model, create the relationship students:

class Teacher extends Model
{
    public function students()
    {
        return $this->hasMany(Student::class, 'teacher_id');
    }
}

In your controller you can do the following:

public function example(){
    $teachers = Teacher::where('teacher_status','active')->withCount('students')->get();
    
    return view('teacherViewExample', compact('teachers'));
}

In your view (teacherViewExample):

<table>
  <thead>
    <tr>
      <th>Teacher Name</th>
      <th>Students Count</th>
    </tr>
  </thead>
  <tbody>
    @foreach($teachers as $teacher)
    <tr>
      <td>{{ $teacher->name }}</td>
      <td>{{ $teacher->students_count }}</td>
    </tr>
    @endforeach
  </tbody>
</table>

Full documentation on how to use withCount() here: https://laravel.com/docs/9.x/eloquent-relationships#counting-related-models

Sometimes you may want to count the number of related models for a given relationship without actually loading the models. To accomplish this, you may use the withCount method. The withCount method will place a {relation}_count attribute on the resulting models:

Answer 3

In case frontend and backend are separated, ie Laravel for backend, Angular for frontend, below are examples for Laravel:

In api.php,

Route::get('teacher-with-students-count', 'TeacherController@getTeacherWithStudentsCount');
 

In Teacher.php (model)

class Teacher extends Model
{
    public function students()
    {
        return $this->hasMany(Student::class, 'teacher_id', 'id');
    }
}

In TeacherController.php

public function getTeacherWithStudentsCount()
    {
        $teachers = Teacher::where('teacher_status','active')->withCount('students')->get();

        return $this->giveSuccessResponse($teachers);
    }