实体框架一对多自引用关系

Question

This is my application's model:

public class Email
{
    public int Id {get; set;}

    public string Content {get; set;}

    public string Address {get; set;}
}

I want to add the option to response to an email (Chain of emails - responses) should it look like this?:

public class Email
{
    public int Id {get; set;}

    public string Content {get; set;}

    public string Address {get; set;}

    public int? PreviousEmailId {get; set;}

    public virtual Email PreviousEmail {get; set;}

    public virtual List<Email> Responses {get; set;}
}

The response email can be a response to another email and so on.. just like an email application

I want to have the possibility to get an email and display all of the emails it is referred to, as a chain, to my clients. And just like in real Email application, when deleting an email, All of the chain should be deleted as well.

Can anyone tell me how should I define the model (I'm using EF 6 code first). How should I define the relations? What is the best practice?

I hope it's clear enough, it's similar concept to how other Email application's work.

Thanks!

Answer 1

You can solve this issue by two ways

first solution: same as you proposed which called a recursive relations "self relation", to store an optional reference to the parent Email "Previous Email" in your case as follow:

public class Email
{
     public int Id {get; set;}
     public int? PrevousEmailId {get; set;}
     // other properties

     public virtual Email PreviousEmail{get;set;}
}

second solution: to store the relation in a separate table that will allow you to response to many recipients at the same time for example and its a general solution of the recursive relation or graph relation ship as follows:

public class Email
{
     public int Id {get; set;}
     // other properties
}

public class EmailResponse
{
     public int EmailId {get; set;}
     public int PreviousEmailId {get; set;}

     public virtual Email Email {get; set;}
     public virtual Email PreviousEmail {get; set;}
}

I hope this will help you