How can I find where a table comes from, since a table shows up, but is not being declared anywhere? - entity-framework

Question

In my .NET Core 5 app I tried to implement a chat, so I created 3 tables - Chats, Messages and UsersChats and 3 corresponding models Chat, Message, UserChat.
However, a bit after I migrated and proceeded with writing code I saw that there was one more table created - ChatUser with two columns - ChatsId and UsersId and they were being populated with chats and users and the UserChat was all null.
So, I thought that I should delete the ChatUser table and see what happens. It turns out that the this.data.SaveChanges(); throws and exception, because it tries to save the data to the ChatUser table. Therefore I returned the table and tried to find where it comes from, but I have not created a model for it, I have not created a DbSet for it or anything, so it is a mystery to me how it came alive.
Here are my 3 models:
public class Chat
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Message> Messages { get; set; } = new List<Message>();
public ICollection<User> Users { get; set; } = new List<User>();
public IEnumerable<UserChat> UserChats { get; set; }
}
public class Message
{
public int Id { get; set; }
public int ChatId { get; set; }
[JsonIgnore]
public Chat Chat { get; set; }
public string UserId { get; set; }
public User User { get; set; }
public string Content { get; set; }
public DateTime CreatedAt { get; set; }
}
public class UserChat
{
public string UserId { get; set; }
public User User { get; set; }
public int ChatId { get; set; }
public Chat Chat { get; set; }
}
Here is the User model:
public class User : IdentityUser
{
[JsonIgnore]
public ICollection<Chat> Chats { get; set; } = new List<Chat>();
public IEnumerable<UserChat> UserChats { get; set; }
}
The DB Sets:
public DbSet<Chat> Chats { get; set; }
public DbSet<Message> Messages { get; set; }
public DbSet<UserChat> UsersChats { get; set; }
The Relations:
builder
.Entity<Message>()
.HasOne(m => m.Chat)
.WithMany(c => c.Messages)
.HasForeignKey(m => m.ChatId)
.OnDelete(DeleteBehavior.Restrict);
builder
.Entity<UserChat>()
.HasKey(uc => new { uc.UserId, uc.ChatId });
The method in which the error occurs:
public void AddUserToChat(string userId, string chatName) {
var chatId = this.data
.Chats
.Where(c => c.Name == chatName)
.Select(c => c.Id)
.FirstOrDefault();
var user = this.data
.Users
.Where(c => c.Id == userId)
.FirstOrDefault();
var chat = this.data
.Chats
.Where(c => c.Name == chatName)
.FirstOrDefault();
chat.Users.Add(user);
this.data.SaveChanges();
}
And finally - what I have in my migration:
migrationBuilder.CreateTable(
name: "Chats",
columns: table => new {
Id = table.Column < int > (type: "int", nullable: false)
.Annotation("SqlServer:Identity", "1, 1"),
Name = table.Column < string > (type: "nvarchar(max)", nullable: true)
},
constraints: table => {
table.PrimaryKey("PK_Chats", x => x.Id);
});
migrationBuilder.CreateTable(
name: "ChatUser",
columns: table => new {
ChatsId = table.Column < int > (type: "int", nullable: false),
UsersId = table.Column < string > (type: "nvarchar(450)", nullable: false)
},
constraints: table => {
table.PrimaryKey("PK_ChatUser", x => new {
x.ChatsId, x.UsersId
});
table.ForeignKey(
name: "FK_ChatUser_AspNetUsers_UsersId",
column: x => x.UsersId,
principalTable: "AspNetUsers",
principalColumn: "Id",
onDelete: ReferentialAction.Cascade);
table.ForeignKey(
name: "FK_ChatUser_Chats_ChatsId",
column: x => x.ChatsId,
principalTable: "Chats",
principalColumn: "Id",
onDelete: ReferentialAction.Cascade);
});
migrationBuilder.CreateTable(
name: "Messages",
columns: table => new {
Id = table.Column < int > (type: "int", nullable: false)
.Annotation("SqlServer:Identity", "1, 1"),
ChatId = table.Column < int > (type: "int", nullable: false),
UserId = table.Column < string > (type: "nvarchar(450)", nullable: true),
Content = table.Column < string > (type: "nvarchar(max)", nullable: true),
CreatedAt = table.Column < DateTime > (type: "datetime2", nullable: false)
},
constraints: table => {
table.PrimaryKey("PK_Messages", x => x.Id);
table.ForeignKey(
name: "FK_Messages_AspNetUsers_UserId",
column: x => x.UserId,
principalTable: "AspNetUsers",
principalColumn: "Id",
onDelete: ReferentialAction.Restrict);
table.ForeignKey(
name: "FK_Messages_Chats_ChatId",
column: x => x.ChatId,
principalTable: "Chats",
principalColumn: "Id",
onDelete: ReferentialAction.Restrict);
});
migrationBuilder.CreateTable(
name: "UserChat",
columns: table => new {
UserId = table.Column < string > (type: "nvarchar(450)", nullable: false),
ChatId = table.Column < int > (type: "int", nullable: false)
},
constraints: table => {
table.PrimaryKey("PK_UserChat", x => new {
x.UserId, x.ChatId
});
table.ForeignKey(
name: "FK_UserChat_AspNetUsers_UserId",
column: x => x.UserId,
principalTable: "AspNetUsers",
principalColumn: "Id",
onDelete: ReferentialAction.Restrict);
table.ForeignKey(
name: "FK_UserChat_Chats_ChatId",
column: x => x.ChatId,
principalTable: "Chats",
principalColumn: "Id",
onDelete: ReferentialAction.Restrict);
});
migrationBuilder.CreateIndex(
name: "IX_ChatUser_UsersId",
table: "ChatUser",
column: "UsersId");
migrationBuilder.CreateIndex(
name: "IX_Messages_ChatId",
table: "Messages",
column: "ChatId");
migrationBuilder.CreateIndex(
name: "IX_Messages_UserId",
table: "Messages",
column: "UserId");
migrationBuilder.CreateIndex(
name: "IX_UserChat_ChatId",
table: "UserChat",
column: "ChatId");
}

Answer 1

Turns out that due to the navigational properties I have in Chat EF Core gets confused. The newer versions of EF Core automatically create the mapping table for you, so to fix it you can either remove the navigational properties and create the mapping table yourself, or you keep the navigational properties and leave EF do it's job.