一对一的实体框架具有其他属性

Question

I am new to EF and have got a very basic question. Can someone please advise how to implement below scenario using Code First approach ?

    public class Book
    {
       public int Id {get; set;}
       public string title {get; set;}
       public string author {get; set;}
       public DateTime DateBorrowed {get; set;}
       public DateTime DateReturned {get; set;}

       public virtual User Borrower {get;set;}
    }
    public class User
    {
       public int Id {get;set;}
       public string UserName {get;set;}
       public string Email {get; set;}

       public virtual ICollection<Book> Books {get; set;}
    }

I would like to maintain both the Book and User classes/underlying tables maintain a unique collection of records every time. In other words, how do we separate DateBorrowed and DateReturned properties in a separate class so that book borrowing and returning transactions would be maintained in a separate SQL table.

Answer 1

Current setup will only allow each book to have one single record of when it was borrowed and when it was returned. Every time its borrowed or returned, it will overwrite the last one. What you're probably looking to do is more along the lines to creating a class that holds the two dates, and then reference that class as a foreign key in your Book table.

Your current table may change like so (code not tested):

public class Book
{
   public int BookId {get; set;}
   public string title {get; set;}
   public string author {get; set;}

   public virtual ICollection<BorrowingRecord> BorrowingRecords { get; set; }

   public int UserId { get; set; }
   public virtual User Borrower {get;set;}
}

public class BorrwingRecord
{
    public int BorrowingRecordId {get; set; }
    public DateTime DateBorrowed {get; set;}
    public DateTime DateReturned {get; set;}

    public int BookId { get; set; }
    public virtual Book Book { get; set; }
}

public class User
{
   public int UserId {get;set;}
   public string UserName {get;set;}
   public string Email {get; set;}

   public virtual ICollection<Book> Books {get; set;}
}

You already have the right idea with your User table. Just set up the connections and you're good to go.

What you're looking for is a One-to-Many relationship. Consult this page for more detail on it: https://msdn.microsoft.com/en-us/data/jj713564.aspx

Here's an example of how you'd get books borrowed by a given user and the borrowing record of those books (code not tested and assumes you've set up your context):

var booksForUser = context.Books.Where(b => b.UserId == GivenUserID);

foreach(var book in booksForUser)
{
    var borrowingRecordForBook = context.BorrowingRecords.Where(br => br.BookId == book.BookId);

    // do what you need with this data.
}