I can't get Tweet Replies from database on my .NET 7.0 Web API

I am making a Twitter Clone API. When I try to get a Tweet by Id with its replies, it returns null even if there is a reply.
Tweet.cs

using TwitterCloneApp.Core.Interfaces;

namespace TwitterCloneApp.Core.Models
{
    public class Tweet : IBaseEntity, IDeletable, IUpdatedAt, ICreatedAt
	{
		public int Id { get; set; }
		public int UserId { get; set; }
		public string Content { get; set; }
		public User User { get; set; }
		public bool isMainTweet { get; set; }
		public bool IsDeleted { get; set; } = false;
        public DateTime? DeletedAt { get; set; }
		public DateTime? UpdatedAt { get; set; }
		public DateTime? CreatedAt { get; set; }
        public ICollection<Tag>? Tags { get; set; } // Many-to-Many ilişkisi için koleksiyon
		public ICollection<Tweet>? Replies { get; set; }
		public ICollection<Like>? Likes { get; set; }
    }
}

TwReply.Cs (for relation)

namespace TwitterCloneApp.Core.Models
{
    public class TwReply
    {
        public int TweetId { get; set; }
        public int ReplyId { get; set; }
        public Tweet Tweet { get; set; }
        public Tweet Reply { get; set; }
    }
}

TweetDto.cs

using TwitterCloneApp.DTO.Tag;
using TwitterCloneApp.DTO.User;

namespace TwitterCloneApp.DTO.Tweet
{
    public class TweetDto
	{
        public int Id { get; set; }
		public UserResponseDto User { get; set; }
		public string? Content { get; set; }
        public DateTime? CreatedAt { get; set; }
        public int LikeCount { get; set; }
		public List<TagResponseDto>? Tags { get; set; }
        public List<ReplyResponseDto>? Replies { get; set; }
    }
}

ReplyResponseDto.cs

using TwitterCloneApp.DTO.User;

namespace TwitterCloneApp.DTO.Tweet
{
    public class ReplyResponseDto
    {
        public UserResponseDto User { get; set; }
        public string Content { get; set; }
        public DateTime? CreatedAt { get; set; }
        public int LikeCount { get; set; }
    }
}

UserResponseDto.cs

namespace TwitterCloneApp.DTO.User
{
	public class UserResponseDto
	{
        public string UserName { get; set; }
        public string DisplayName { get; set; }
        public string? ProfileImg { get; set; }
    }
}

TweetController part

[HttpGet("[action]")]
public async Task<IActionResult> GetTweetByIdAsync(int id)
{
	var tweet = await _tweetService.GetTweetByIdAsync(id);
	return Ok(tweet);
}

TweetService part

public async Task<TweetDto> GetTweetByIdAsync(int tweetId)
{
	return await _tweetRepository.GetTweetWithTagsByIdAsync(tweetId);
}

TweetRepository part

public async Task<TweetDto> GetTweetWithTagsByIdAsync(int tweetId)
{
	var tweet = await _tweet.Include(t => t.Tags)
							.Include(t => t.Replies).ThenInclude(reply => reply.User)
							.Include(t => t.User)
							.Include(t => t.Likes)
							.FirstOrDefaultAsync(t => t.Id == tweetId);

	if (tweet == null)
	{
		return null; // veya gerekli işlemleri yapın
	}

	var tweetDto = new TweetDto
	{
		Id = tweet.Id,
		Content = tweet.Content,
		CreatedAt = tweet.CreatedAt,
		LikeCount = tweet.Likes?.Count ?? 0,
		Tags = tweet.Tags?.Select(t => new TagResponseDto
		{
			Name = t.Name
		}).ToList(),
		User = new UserResponseDto
		{
			UserName = tweet.User.UserName,
			DisplayName = tweet.User.DisplayName,
			ProfileImg = tweet.User.ProfileImg
		},
		Replies = tweet.Replies?.Select(reply => new ReplyResponseDto
		{
			User = new UserResponseDto
			{
				UserName = reply.User.UserName,
				DisplayName = reply.User.DisplayName,
				ProfileImg = reply.User.ProfileImg
			},
			Content = reply.Content,
			CreatedAt = reply.CreatedAt,
			LikeCount = reply.Likes?.Count ?? 0
		}).ToList()
	};

	return tweetDto;
}

AppDbContext.cs

using Microsoft.EntityFrameworkCore;
using System.Reflection;
using TwitterCloneApp.Core.Models;

namespace TwitterCloneApp.Repository
{
    public class AppDbContext : DbContext
    {
        public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
        { 
        }
        public DbSet<User> Users { get; set; }
        public DbSet<Tweet> Tweets { get; set; }
        public DbSet<Tag> Tags { get; set; }
        public DbSet<Like> Likes { get; set; }
        public DbSet<TwReply> TwReplies { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.ApplyConfigurationsFromAssembly(Assembly.GetExecutingAssembly());
            
            var relationships = modelBuilder.Model.GetEntityTypes()
                .SelectMany(e => e.GetForeignKeys());

            foreach (var relationship in relationships)
            {
                relationship.DeleteBehavior = DeleteBehavior.Restrict;
            }
            base.OnModelCreating(modelBuilder);
        }

    }
}

There are 2 replies (3 and 10) for Tweet Id:1
but output is:

{
  "id": 1,
  "user": {
    "userName": "asdasdasd",
    "displayName": "asdasdasd",
    "profileImg": "string"
  },
  "content": "First tweet",
  "createdAt": null,
  "likeCount": 3,
  "tags": [
    {
      "name": "#testingSeed1"
    },
    {
      "name": "#testingSeed2"
    },
    {
      "name": "#testing"
    }
  ],
  "replies": []
}

I tried to get replies while getting a Tweet by Id but the program doesn't get Replies. I checked how does it work with breakpoints and it seems problem is in TweetRepository part. It returns nothing for Replies when it gets entity. I use Entity Framework Core BTW.

The entity Tweet (simplified) is :

public class Tweet
{
    public int Id { get; set; }
    public string Content { get; set; } = "";
    public ICollection<Tweet>? Replies { get; set; }
}

Then EF Core will tanlaste this model to this DB Schema :

CREATE TABLE [Tweets] (
    [Id] int NOT NULL,
    [Content] nvarchar(max) NOT NULL,
    [TweetId] int NULL,
    CONSTRAINT [PK_Tweets] PRIMARY KEY ([Id]),
    CONSTRAINT [FK_Tweets_Tweets_TweetId] FOREIGN KEY ([TweetId]) REFERENCES [Tweets] ([Id])
);

When the DB schema isn't specified, EF Core use convention to determine the DB schema. And the convention for a collection navigation property to the same entity is 1 to n (a tweet can have manyreplies, but can reply to only one tweet). It's like the model was :

public class Tweet
{
    public int Id { get; set; }
    public string Content { get; set; } = "";
    public ICollection<Tweet>? Replies { get; set; }
    public Tweet ReplyTo { get; set; }
}

You can refer to the documentatino EF Core : Conventions for relationship discovery for more information about the convention about relationship.

In you case, it's a relation n to n (a tweet can have many reply and can reply to many tweet) by the intermediate entity TwReply.

By convention, the model will be :

public class Tweet
{
    public int Id { get; set; }
    public string Content { get; set; } = "";
    public ICollection<TwReply>? Replies { get; set; }
}

public class TwReply
{
    public int Id { get; set; }
    public Tweet Tweet { get; set; }
    public Tweet Reply { get; set; }
}

If you want keep your model, you need to specify manually the relation like :

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    ...
    modelBuilder.Entity<Tweet>()
        .HasMany(t => t.Replies)
        .WithMany()
        .UsingEntity<TwReply>(
            i => i.HasOne(tr => tr.Reply).WithMany(),
            i => i.HasOne(tr => tr.Tweet).WithMany()
        );
}