sam-api/app/Models/Commons/DepartmentUser.php

<?php

namespace App\Models\Commons;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;
use App\Traits\BelongsToTenant;
use App\Traits\ModelTrait;
use App\Models\Members\User;

/**
 * @mixin IdeHelperDepartmentUser
 */
class DepartmentUser extends Model
{
    use SoftDeletes, BelongsToTenant, ModelTrait;

    protected $table = 'department_user';
    protected $fillable = [
        'tenant_id','department_id','user_id','is_primary','joined_at','left_at',
    ];

    protected $casts = [
        'tenant_id'     => 'integer',
        'department_id' => 'integer',
        'user_id'       => 'integer',
        'is_primary'    => 'integer',
        'joined_at'     => 'datetime',
        'left_at'       => 'datetime',
    ];

    public function department()
    {
        return $this->belongsTo(Department::class, 'department_id');
    }

    public function user()
    {
        // User 네임스페이스가 다르면 여기만 맞춰줘.
        return $this->belongsTo(User::class, 'user_id');
    }
}