web api c# asp.net core post to two tables

Question

How to do post record to tables with many-to-many relationship I have table books, authors and Book_Author. Please help.

Sachin Singh · Answer

If you are using EF then public class LibraryDAL { private LibraryContext db; public LibraryDAL() { db= new LibraryContext(); // your context class } public void AddBooks(Book book) { db.Books.Add(book); db.SaveChanges(); } public void AddAuthors(Author author) { db.Authors.Add(author); db.SaveChanges(); } public void AddBooksToExistingAuthor( int authorId, Book book) { var author= db.Authors.Find(authorId); author.Books.Add(book); // this will create a new row to bridge table db.SaveChanges(); } public void AddAuthorToExistingBook( int bookId, Author author) { var book= db.Books.Find(bookId); book.Authors.Add(author); // this will create a new row to bridge table db.SaveChanges(); } } I discussed the 4 scenarios, 1. Add new book 2. Add new Author 3. Add Author to Existing Book and 4. Add Book to existing Author. The last two methods are used to fill the many-to-many table using EF.

Nitin Sontakke · Answer

The trick here is to create an container class, which has all the data you want to post. Once data is received on WebAPI side, you can disintegrate it and store it in different tables. You know the data and you know which part of the class should go to which table. Hope it helps. If it is not clear please do let me know.

Marina · Answer

Thank you for a very good explanation. I am trying to write post of a new book which possibly may have more than one author. This is BookRepository: namespace MyBookWebAPI.Repository { public class BookRepository : IBookRepository { private readonly MyBookWebApiContext _context; public BookRepository(MyBookWebApiContext context) { _context = context; } public async Task > GetAllBooksAsync() { var records = await _context.Books.ToListAsync(); return records; } public async Task GetBookByIdAsync(int bookId) { var records = await _context.Books.Where(x => x.Id == bookId).Select(x => new Book() { Id = x.Id, Title = x.Title, PublisherId = x.PublisherId }).FirstOrDefaultAsync(); return records; } public async Task AddBookAsync(List authorsId, Book book) { var authors = _context.Authors.Where(a => authorsId.Contains(a.Id)).ToList(); foreach (var author in authors) { var bookAuthor = new Book_Author() { Author = author, Book = book }; _context.Add(bookAuthor); _context.Books.Add(book); await _context.SaveChangesAsync(); return book.Id; } } } } AddBookAsync gives an error "not all code paths retrutn a value. Can you, please, advise what can I do?