Alexander-Shein / CommentManagement

CommentManagement

• Deployed here: https://comment-management.polandcentral.cloudapp.azure.com/swagger/index.html

• Architecture details: https://github.com/Alexander-Shein/EmpCore

It's subscribed to 2 integration events from BlogPostManagementService

• BlogPostPublishedEvent once this event is received CommentManagementService enables leaving comments on a published blog post.
• BlogPostDeletedEvent once this event is received CommentManagementService deletes all the comments for a deleted blog post and disables leaving comments.

API endpoints

FYI: Put version 1 everywhere when you test

• GET /v{version}/comments - searches for comments. Returns paged list. Can be filtered by BlogPostId
• POST /v{version}/comments - it creates a new comment on published blog post. You can leave comments only when BlogPostPublishedEvent is received. Domain Model with implementation:

public class PublishedBlogPost : AggregateRoot<Guid>
{
    public static Result<PublishedBlogPost> Create(Guid id)
    {
        if (id == Guid.Empty) return EmptyBlogPostIdFailure.Instance;
        return new PublishedBlogPost{Id = id};
    }
    
    public Result<Comment> Comment(Commentor commentor, Message message)
    {
        var comment = new Comment(this,
            commentor ?? throw new ArgumentNullException(nameof(commentor)),
            message ?? throw new ArgumentNullException(nameof(message)));

        return Result.Ok(comment);
    }
}

As you can see here PublishedBlogPost has method Comment. It means that it's possible to create a new comment only if you have PublishedBlogPost object.

• PUT /v{version}/comments/{commentId}/replies - creates a replay on a comment. Domain Model with implementation:

public class Comment : AggregateRoot<long>
{
    private Comment() { }

    public PublishedBlogPost PublishedBlogPost { get; private set; }
    public Commentor Commentor { get; private set; }
    public Comment? ParentComment { get; private set; }
    public Message Message { get; private set; }
    
    public DateTime CreatedAt { get; private set; }
    public DateTime UpdatedAt { get; private set; }

    internal Comment(
        PublishedBlogPost publishedBlogPost,
        Commentor commentor,
        Message message,
        Comment? parentComment = null)
    {
        var now = DateTime.UtcNow;

        PublishedBlogPost = publishedBlogPost ?? throw new ArgumentNullException(nameof(publishedBlogPost));
        Commentor = commentor ?? throw new ArgumentNullException(nameof(commentor));
        Message = message ?? throw new ArgumentNullException(nameof(message));
        ParentComment = parentComment;
        CreatedAt = now;
        UpdatedAt = now;
    }

    public Result<Comment> Reply(Commentor commentor, Message message)
    {
        var comment = new Comment(PublishedBlogPost,
            commentor ?? throw new ArgumentNullException(nameof(commentor)),
            message ?? throw new ArgumentNullException(nameof(message)),
            this);

        return comment;
    }
}

As you can see it's possible to create a reply only if you have a comment object. No other way because everything is encapsulated and private/internal constructors won't allow you to create an instance in invalid state.

P.S. Sometimes code return Result and sometimes it throws an exception. The difference between them is if it throws an exception it's a bug in code. If it returns a Result object - it's a validation failure. Before you decide to return a Result or to throw an error you need to ask a question - Can a user do something with it? If yes - return a Result object. If no - throw an exception.

CommentManagement DB schema

CREATE TABLE [dbo].[PublishedBlogPost]
(
  [Id]				UNIQUEIDENTIFIER NOT NULL

  CONSTRAINT [PK_PublishedBlogPost_Id] PRIMARY KEY (Id)
);

CREATE TABLE [dbo].[Commentor]
(
  [Id]				 VARCHAR(128) NOT NULL,
  [UserName]   NVARCHAR(256) NOT NULL CONSTRAINT [DF_Commentor_UserName] DEFAULT '',

  CONSTRAINT [PK_Commentor_Id] PRIMARY KEY (Id)
);

CREATE TABLE [dbo].[Comment]
(
  [Id]					        BIGINT IDENTITY(1,1) NOT NULL,
  [PublishedBlogPostId]	UNIQUEIDENTIFIER NOT NULL,
  [CommentorId]			    VARCHAR(128) NOT NULL,
  [ParentCommentId]		  BIGINT NULL,
  [Message]				      NVARCHAR(1024) NOT NULL		CONSTRAINT [DF_Comment_Message] DEFAULT '',
  [CreatedAt]				    DATETIME2 NOT NULL			CONSTRAINT [DF_Comment_CreatedAt] DEFAULT GETDATE(),
  [UpdatedAt]				    DATETIME2 NOT NULL			CONSTRAINT [DF_Comment_UpdatedAt] DEFAULT GETDATE(),

  CONSTRAINT [PK_Comment_Id] PRIMARY KEY (Id),
  CONSTRAINT [FK_Comment_PublishedBlogPostId_PublishedBlogPost_Id] FOREIGN KEY ([PublishedBlogPostId]) REFERENCES [dbo].[PublishedBlogPost]([Id]),
  CONSTRAINT [FK_Comment_CommentorId_Commentor_Id] FOREIGN KEY ([CommentorId]) REFERENCES [dbo].[Commentor]([Id]),
  CONSTRAINT [FK_Comment_ParentCommentId_Comment_Id] FOREIGN KEY ([ParentCommentId]) REFERENCES [dbo].[Comment]([Id])
);