不是重复:请参阅评论和回答这个问题。ASP.Net核心NullReferenceException未由用户处理
我几乎是ASP.net核心开发的新手。我正在用MySql作为我的数据库构建一个示例web api。
的My Book型号:
public class Book
{
[Key]
public long Id { get; set; }
[Required]
public string Name { get; set; }
[Required]
public string Author { get; set; }
public DateTime CreatedOn { get; set; } = DateTime.UtcNow;
public Book()
{
}
}
public class WebAPIDataContext : DbContext
{
public WebAPIDataContext(DbContextOptions<WebAPIDataContext> options)
: base(options)
{
}
public DbSet<Book> Books { get; set; }
}
图书库:
public class BookRepository: IBookRepository
{
private readonly WebAPIDataContext _db;
public BookRepository(WebAPIDataContext db) {
_db = db;
}
public Book CreateBook(Book book) {
_db.Books.Add(book);
_db.SaveChanges();
return book;
}
public void DeleteBook(long id)
{
Book book = GetBook(id);
if (book != null) {
_db.Books.Remove(book);
_db.SaveChanges();
}
}
public List<Book> GetAllBooks()
{
return _db.Books.AsNoTracking().ToList();
}
public Book GetBook(long id)
{
return _db.Books.FirstOrDefault(o => o.Id == id);
}
public void UpdateBook(long id, Book book)
{
throw new NotImplementedException();
}
}
public interface IBookRepository
{
List<Book> GetAllBooks();
Book GetBook(long id);
Book CreateBook(Book book);
void UpdateBook(long id, Book book);
void DeleteBook(long id);
}
并预定控制器:
[Route("api/[controller]")]
public class BooksController : Controller
{
private readonly IBookRepository _books;
[HttpGet("")]
public IActionResult GetAllBooks()
{
List<Book> books = _books.GetAllBooks();
return Ok(books);
}
[HttpGet("{id}")]
public IActionResult GetBook(long id)
{
Book book = _books.GetBook(id);
if (book == null)
{
return NotFound();
}
return Ok(book);
}
[HttpPost]
public IActionResult CreateBook([FromBody] Book book)
{
if (ModelState.IsValid == false)
{
return BadRequest(ModelState);
}
Book createdBook= _books.CreateBook(book);
return CreatedAtAction(
nameof(GetBook), new { id = createdBook.Id }, createdBook);
}
[HttpPut("{id}")]
public IActionResult UpdateBook(long id, [FromBody] Book book)
{
if (ModelState.IsValid == false)
{
return BadRequest(ModelState);
}
try
{
_books.UpdateBook(id, book);
return Ok();
}
catch (EntityNotFoundException<Book>)
{
return NotFound();
}
}
[HttpDelete("{id}")]
public IActionResult DeleteBook(long id)
{
_books.DeleteBook(id);
return Ok();
}
}
当我从扬鞭POST请求创建一个新的书它给我NullReferenceException
错误。我究竟做错了什么?
嗯,我试图处理null建议在这篇文章,但没有帮助。 – Nitish
您将控制器类中的_books分配给实现的位置?现在它在运行时没有初始化状态。除非你在构造函数中使用DI,否则不会发生这种情况,假设是你尝试去的路线。不是杜佩......只是误解他为什么在他的情况。 – mvermef
这是我第一次尝试使用ASP.net Core,我正在关注本教程(https://joonasw.net/view/building-a-basic-web-api-on-asp-net-core)。我基本上尝试了与他相同的逻辑,但使用不同的模型。也许你可以给我正确的方式? – Nitish