【C#/Blazor】実務Webアプリ開発編 (23)DDDのドメインサービスとは？～集約をまたぐビジネスルール～

src/MentorApp.Domain/
  Models/
    Users/
      User.cs
      IUserRepository.cs
    Mentorships/
      Mentorship.cs
      IMentorshipRepository.cs
    Topics/
      Topic.cs
      ITopicRepository.cs
    Shared/
      IUnitOfWork.cs
      IUnitOfWorkFactory.cs
  Services/  ←ドメインサービスを配置するフォルダ
    MentorshipDuplicationCheckService.cs
    RoleChangeValidationService.cs 

public class MentorshipDuplicationCheckService
{
    public void ValidateMentorshipCreation(
        User mentor,
        User mentee,
        bool hasActiveMentorshipForPair)
    {
        if (mentor.Role != Role.Mentor)
            throw new InvalidOperationException(...);

        if (mentee.Role != Role.Mentee)
            throw new InvalidOperationException(...);

        if (mentor.Id == mentee.Id)
            throw new InvalidOperationException(...);

        if (hasActiveMentorshipForPair)
            throw new InvalidOperationException(...);
    }
}

public class RoleChangeValidationService
{
    public void Validate(
        User user,
        Role newRole,
        bool participatesInActiveMentorship)
    {
        if (user.Role == newRole)
            return;

        if (participatesInActiveMentorship)
        {
            throw new InvalidOperationException(
                "Active なメンタリング関係が存在するため、ロールを変更できません。...");
        }
    }
}

await using var uow = await unitOfWorkFactory.CreateAsync(cancellationToken);

var mentor = await uow.Users.FindByIdAsync(request.MentorUserId, cancellationToken)
    ?? throw new ArgumentException(...);

var mentee = await uow.Users.FindByIdAsync(request.MenteeUserId, cancellationToken)
    ?? throw new ArgumentException(...);

var hasActiveMentorshipForPair = await uow.Mentorships.HasActiveMentorshipAsync(
    mentor.Id,
    mentee.Id,
    cancellationToken);

// ★ここでドメインサービスを使う
// 集めてきた判断材料をドメインサービスへ渡して、判断をゆだねる
duplicationCheckService.ValidateMentorshipCreation(
    mentor,
    mentee,
    hasActiveMentorshipForPair);

var mentorship = new Mentorship(request.MentorUserId, request.MenteeUserId, now);
await uow.Mentorships.AddAsync(mentorship, cancellationToken);
await uow.SaveChangesAsync(cancellationToken);

await using var uow = await unitOfWorkFactory.CreateAsync(cancellationToken);

var user = await uow.Users.FindByIdAsync(request.UserId, cancellationToken)
    ?? throw new KeyNotFoundException(...);

var participatesInActiveMentorship = await uow.Mentorships.HasAnyActiveMentorshipByUserIdAsync(
    user.Id,
    cancellationToken);

// ★ここでドメインサービスを使う
// 集めてきた判断材料をドメインサービスへ渡して、判断をゆだねる
roleChangeValidation.Validate(user, request.NewRole, participatesInActiveMentorship);
user.ChangeRole(request.NewRole);

await uow.SaveChangesAsync(cancellationToken);

var hasDisplayNameChanged = request.DisplayName != user.DisplayName;
var hasRoleChanged = request.Role != user.Role;

if (hasDisplayNameChanged)
{
    user.UpdateDisplayName(request.DisplayName);
}

if (hasRoleChanged)
{
    var participatesInActiveMentorship = await uow.Mentorships.HasAnyActiveMentorshipByUserIdAsync(
        user.Id,
        cancellationToken);

    // ★ここでドメインサービスを使う
    // 集めてきた判断材料をドメインサービスへ渡して、判断をゆだねる
    roleChangeValidation.Validate(user, request.Role, participatesInActiveMentorship);
    user.ChangeRole(request.Role);
}

await uow.SaveChangesAsync(cancellationToken);