public static void AddAuthors()
{
var author1 = new Author
{
FirstName = "Charles",
LastName = "Dickens"
};
var author2 = new Author
{
FirstName = "Ernest",
LastName = "Hemingway"
};
var author3 = new Author
{
FirstName = "José",
LastName = "Saramago"
};
var authors = new List <Author>();
authors.Add(author1);
authors.Add(author2);
authors.Add(author3);
using (var ctx = new EFC.BooksDbContext())
{
if (ctx.Authors.Count() == 0)
{
ctx.Authors.AddRange(authors);
ctx.SaveChanges();
}
}
}
public static void AddToEFCTest()
{
var shelf = new Shelf();
shelf.ShelfId = 0;
shelf.Description = "New Shelf";
shelf.ShelfBooks = new List <ShelfBook>();
var sb1 = new ShelfBook
{
ShelfId = 0,
Book = new Book
{
BookId = 100,
Author = new Author
{
AuthorId = 2,
FirstName = "Existing Author",
LastName = "2"
},
Title = "Existing Book1"
}
};
shelf.ShelfBooks.Add(sb1);
var sb2 = new ShelfBook
{
ShelfId = 0,
Book = new Book
{
BookId = 200,
Author = new Author
{
AuthorId = 2,
FirstName = "Existing Author",
LastName = "2"
},
Title = "Existing Book2"
}
};
shelf.ShelfBooks.Add(sb2);
using (var ctx = new EFC.BooksDbContext())
{
ctx.Shelfs.Add(shelf); // throws error
// Error:
// System.InvalidOperationException:
// 'The instance of entity type 'Author' cannot be tracked because another instance
// with the key value '{AuthorId: 2}' is already being tracked.
// When attaching existing entities, ensure that only one entity instance
// with a given key value is attached.'
}
}
