slake-school-service/app/Models/ResearchDirection.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsToMany;
use Illuminate\Database\Eloquent\SoftDeletes;

class ResearchDirection extends Model
{
    use SoftDeletes;

    protected $fillable = [
        'name',
        'sort',
        'status',
        'remark',
    ];

    protected $casts = [
        'sort' => 'integer',
        'status' => 'integer',
    ];

    public function adminUsers(): BelongsToMany
    {
        return $this->belongsToMany(
            AdminUser::class,
            'admin_user_research_directions',
            'research_direction_id',
            'admin_user_id'
        );
    }

    public function teachers(): BelongsToMany
    {
        return $this->belongsToMany(
            Teacher::class,
            'teacher_research_direction',
            'research_direction_id',
            'teacher_id'
        );
    }
}