Entity Framework (code first) - Relation one to many

Question

I have trouble with setting a one to many relationship in EF (.net Core) 6.

I have a table with users

public class UserDomain{
   Id{get;set;}
   Name{get;set;}
}

I have a table with messages where I want to track who has seen the messages

public class MessageDomain{
  Id{get;set;}
  Title{get;set;}
  Message{get;set;}
  List<UserDomain> UsersRead{get;set;}
}

Now when I add a migration it sets a column on the user table with an integer of the id of the message. But that is not what I want. Because then the read message switches every time I set a message as read.

I tried

modelBuilder.Entity<MessageDomain>().HasMany(x => x.UsersRead).WithOne().HasForeignKey(x => x.Id);

But that also did not work.

Answer 1

In order to have one-to-many relationship you will have to have that column which will be a FK to the other table.

In your case if MessageDomain needs to have relation ship to many users. You need to add MessageDomainId column in UserDomain class. - it will also generate that column in the db.

But that is not what I want. Because then the read message switches every time I set a message as read.

You will have to update the reference on UserDomain each time that happens

Answer 2

Based on the comment on the answer above you will probably need to create an additional table.

1. UserDomain
2. UserMessages
3. MessagesDomain

Where user will have a one to many relationships with UserMessages and then MessagesDomain will then have One to many relationship with UserMessages.

public class UserDomain
{
   Id{get;set;}
   Name{get;set;}
   List<UserMessages> ReadMessages{get;set;}
}

public class UserMessages
{
   UserId{get;set;}
   MessageId{get;set;}
   MessageDomain MsgDomain{get;set;}
   UserDomain UserDomain{get;set;}
}

public class MessageDomain{
  Id{get;set;}
  Title{get;set;}
  Message{get;set;}
  List<UserMessages> ReadBy{get;set;}
}

You will then use UserMessages to track which user read which message, you can then include the related tables in your query to get all the data.