For illustration purposes, let's consider 3 tables: Question, Answer and Comment with the following ORM models (in C#).

• A question can have zero or more answers and/or comments.
• An answer belongs to a question and can have zero or more comments.
• A comment belongs to either a question or an answer.

The rules mimic SO/SE mechanism.

class Question 
{
  public int Id {get; set;}
  public string Content {get; set;}
  public IEnumerable<Answer> Answers {get; set;}
  public IEnumerable<Comment> Comments {get; set;}
}

class Answer
{
  public int Id {get; set;}
  public string Content {get; set;}
  public Question Question {get; set;}
  public IEnumerable<Comment> Comments {get; set;}
}

class Comment
{
  public int Id {get; set;}
  public string Content {get; set;}
  public ?????? For {get; set;}
}

Question

I have no idea how to construct the Comment table in which the property For can be either Question or Answer. What is the type of For property?

CodePudding user response：

nothing! leave it to EF, it will manage these relations. as a note, I can say the relations are one-to-many each Answer and Question has own Comment so if you want to put foreign keys you must use two keys for both of them