Laravel relationship return null when use with get data

Question

i have two table: class_list 、 teacher_detail i try to use relationship to get data from two table, i can get class_list data correctly but when i use with() to get teacher_detail data, it will return null.

how can i get teacher_detail data?

ClassListModel

  protected $fillable = [
        'CLASS_NAME',
        'IMG_SRC',
        'TEACHER_ID',
        'DESCRIBE',
        'START_DATE',
        'CLASS_WEEK_DAY',
        'START_TIME',
        'END_TIME',
        'CREATETIME',
        'CREATOR',
        'LASTUPDATE',
        'MODIFIER'
      ];

      public $primaryKey = 'id';

      protected $dateFormat = 'Y-m-d';

      public $timestamps = false;

      protected $table = 'class_list';
      public function teacherElement(){
        return $this->belongsTo(TeacherDetailModel::class,'teacher_id','id')->select(['id','name','graduated_school']);
      }

TeacherDetailModel

  protected $fillable = [
    'NAME',
    'GRADE_SCHOOL',
    'EXPERTISE',
    'EMAIL',
    'CREATETIME',
    'CREATOR',
    'LASTUPDATE',
    'MODIFIER'
  ];

  public $primaryKey = 'id';

  protected $dateFormat = 'Y-m-d';

  public $timestamps = false;

  protected $table = 'TEACHER_DETAIL';
  public function ClassListModelHasMany(){
    return $this->hasMany(ClassListModel::class,'id','teacher_id');
  }

use relationship

  public function show(Request $request)
    {
        //
        $post = $request->post();
        $detail = ClassListModel::where("class_list.id","=",$post['body']['ID'])
                  ->with('teacherElement')
                  ->get();
        return $detail;
    }

foreignId constrained

    Schema::table('TEACHER_DETAIL', function (Blueprint $table) {
      $table->foreignId('id')->constrained('USER', 'id');
    });
    Schema::table('CLASS_LIST', function (Blueprint $table) {
      //
      $table->foreignId('TYPE_ID')->constrained('CLASS_TYPE', 'id');
      $table->foreignId('TEACHER_ID')->constrained('TEACHER_DETAIL','id');
    });

return Value(teacher_element is null) enter image description here

i delete select in teacherElement but it still not work

Answer 1

your relation is incorrect.

change it to on TeacherDetailModel:

 public function ClassListModelHasMany(){
    return $this->hasMany(ClassListModel::class,'teacher_id','id');
  }

also can change query like this:

    $detail = ClassListModel::where('id',$post['body']['ID'])
                  ->with('teacherElement')
                  ->get();
    return $detail;