環境

Laravel v9.5.1 (PHP v8.1.3)

usersテーブル
id - integer
name - string

rolesテーブル
id - integer
name - string

role_userテーブル
user_id - integer
role_id - integer

Pivotを使わない場合

Models/RoleUser.php

class RoleUser extends Model
{
  ...
  public function user(): BelongsTo
  {
	return $this->belongsTo(User::class);
  }

  public function role(): BelongsTo
  {
	return $this->belongsTo(Role::class);
  }
}

Models/User.php

class User extends Model
{
  ...
  public function roleUsers(): HasMany
  {
	return $this->hasMany(RoleUser::class);
  }
}

Models/Role.php

class Role extends Model
{
  ...
  public function roleUsers(): HasMany
  {
	return $this->hasMany(RoleUser::class);
  }
}

userからroleを取得するとき、めちゃくちゃめんどくさいし分かりづらい！

User::first()->roleUsers()->first()->role()->first()

Pivotを使う場合

Models/RoleUser.php

use Illuminate\Database\Eloquent\Relations\Pivot;

class RoleUser extends Pivot
{
  ...
  public function user(): BelongsTo
  {
	return $this->belongsTo(User::class);
  }

  public function role(): BelongsTo
  {
	return $this->belongsTo(Role::class);
  }
}

Models/User.php

class User extends Model
{
  ...
  public function roles(): BelongsToMany
  {
	return $this->belongsToMany(Role::class, 'role_user', 'user_id', 'role_id');
  }
}

Models/Role.php

class Role extends Model
{
  ...
  public function users(): BelongsToMany
  {
	return $this->belongsToMany(User::class, 'role_user', 'user_id', 'role_id');
  }
}

userからroleを取得するとき下記のようにしたら取得できるので、シンプルで分かりやすい！

User::first()->roles()

参考