使用LINQ加载相关实体

Question

I have the following two classes:

Author class:

public class Author
{
    public Author()
    {
        this.Books = new List<Book>();
    }
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public DateTime DOB { get; set; }
    public virtual ICollection<Book> Books { get; set; }
}

And the Book class:

public class Book
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime DatePublished { get; set; }
    public bool IsBorrowed { get; set; }
    public bool IsOverdue { get; set; }
    public int AuthorId { get; set; }
    public virtual Author Author { get; set; }
}

An author can have many books. What I am having trouble with is loading all the books associated with an Author. For example I have an Author in my database with an ID of 1, I want to return all the books associated with that particular Author.

My thought process was that the best way to do this is with LINQ, however I am lost on how to properly create a LINQ query to do this. Could you please guide me on the best way to accomplish said task?

Answer 1

Look here https://msdn.microsoft.com/en-us/library/bb397906.aspx .. Thats a good site to start with.

If you are working with entity framework I´ll recommend https://msdn.microsoft.com/en-us/library/bb399375(v=vs.110).aspx

You need to instantiate the database context first, and after that you can access the specified entity with linq

var dbContext = new DataContext();
var query = from book in dbContext.Books
where book.AuthorId == 1
select book;

After that you can either get your results in a foreach-loop (or such) or executing the methods

.First();

With exceptions or

.FirstOrDefault();

without exceptions.

Answer 2

You need to query the books table. Something like:

IQueryable<Book> books =  
from book in db.Books
where book.AuthorId == 1  
select book;