Web api无法执行任何查询或获取返回数据库表中多个行的方法。我有一个公寓模型类，在其中添加了一个BuyerID，它是Buyers模型类的ID。买方类还包含公寓的集合。它返回此错误：
SqlNullValueException: Data is Null. This method or property cannot be
called on Null values
我的公寓模型课程是：
public class Apartment
{
[Key]
public int ID { get; set; }
public string Title { get; set; }
public int NbofRooms { get; set; }
public int Price { get; set; }
public string Address { get; set; }
public int BuyerId { get; set; }
}
我的买家班级是：
public class Buyer
{
[Key]
public int ID { get; set; }
public string FullName { get; set; }
public int Credit { get; set; }
public ICollection<Apartment> apartments { get; set; }
}
我的公寓管理员是：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Assignment2CME.Data;
using Assignment2CME.Models;
using Microsoft.AspNetCore.Cors;
using System.Diagnostics;
using System.Web.Http.Cors;
namespace Assignment2CME.Controllers
{
[Produces("application/json")]
[Route("api/Apartments")]
[System.Web.Http.Cors.EnableCors(origins: "http://localhost:4200", headers: "*", methods: "*")]
[Microsoft.AspNetCore.Cors.EnableCors("BuyersPolicy")]
public class ApartmentsController : Controller
{
private readonly ApartmentContext _context;
public ApartmentsController(ApartmentContext context)
{
_context = context;
}
// GET: api/Apartments
[HttpGet]
public IEnumerable<Apartment> GetApartments()
{
return _context.Apartments;
}
// GET: api/Apartments/5
[HttpGet("{id}")]
public async Task<IActionResult> GetApartment([FromRoute] int id)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
var apartment = await _context.Apartments.SingleOrDefaultAsync(m => m.ID == id);
if (apartment == null)
{
return NotFound();
}
return Ok(apartment);
}
// GET: api/Apartments/5
[HttpGet("Aparts/{id}")]
public async Task<IActionResult> GetApar([FromRoute] int id)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
var apartment = await _context.Apartments.Select(x => x).ToListAsync();
if (apartment == null)
{
return NotFound();
}
return Ok(apartment);
}
// GET: api/Apartments/5
[HttpGet("Title/{id}")]
public async Task<IActionResult> GetTitle([FromRoute] int id)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
var apartment = await _context.Apartments.SingleOrDefaultAsync(m => m.ID == id);
var title = apartment.Title;
if (apartment == null)
{
return NotFound();
}
return Ok(title);
}
// GET: api/Apartments/address1/5
[HttpGet("address1/{id}")]
public async Task<IActionResult> ReturnAddress([FromRoute] int id)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
var apartment = await _context.Apartments.SingleOrDefaultAsync(m => m.ID == id);
var address = apartment.Address;
if (apartment == null)
{
return NotFound();
}
return Ok(address);
}
// GET: api/Apartments/Price/5
[HttpGet("Price/{id}")]
public async Task<IActionResult> GetPrice([FromRoute] int id)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
var apartment = await _context.Apartments.SingleOrDefaultAsync(m => m.ID == id);
var price = apartment.Price;
if (apartment == null)
{
return NotFound();
}
return Ok(price);
}
[HttpGet("NumberofRooms/{id}")]
public async Task<IActionResult> GetNbofRooms([FromRoute] int id)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
var apartment = await _context.Apartments.SingleOrDefaultAsync(m => m.ID == id);
var NumberofRooms = apartment.NbofRooms;
if (apartment == null)
{
return NotFound();
}
return Ok(NumberofRooms);
}
// GET: api/Apartments/40000/70000
[HttpGet("{fromPrice}/{toPrice}")]
public async Task<IActionResult> GetFilteredApartment([FromRoute] int fromPrice,[FromRoute] int toPrice)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
if (fromPrice != 0 && toPrice != 0)
{
var apartment = await _context.Apartments.Where(s => s.Price >= fromPrice && s.Price <= toPrice).OrderByDescending(s => s.Price).ToListAsync();
if (apartment == null)
{
return NotFound();
}
return Ok(apartment);
}
else if(fromPrice != 0)
{
var apartment = await _context.Apartments.Where(s => s.Price >= fromPrice).ToListAsync();
if (apartment == null)
{
return NotFound();
}
return Ok(apartment);
}
else if (toPrice != 0)
{
var apartment = await _context.Apartments.Where(s => s.Price <= toPrice).ToListAsync();
if (apartment == null)
{
return NotFound();
}
return Ok(apartment);
}
else
{
var apartment = _context.Apartments;
if (apartment == null)
{
return NotFound();
}
return Ok(apartment);
}
}
// GET: api/Apartments/Address/Beirut
[HttpGet("Address/{address}")]
public async Task<IActionResult> GetFilteredApartmentByAddress([FromRoute] string address)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
if (address != null)
{
var apartment = await _context.Apartments.Where(s => s.Address == address).OrderByDescending(s => s.Price).ToListAsync();
if (apartment == null)
{
return NotFound();
}
return Ok(apartment);
}
else
{
var apartment = _context.Apartments;
if (apartment == null)
{
return NotFound();
}
return Ok(apartment);
}
}
// GET: api/Apartments/NbofRooms/5
[HttpGet("NbofRooms/{NbofRooms}")]
public async Task<IActionResult> GetFilteredApartmentByNbofRooms([FromRoute] int NbofRooms)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
if (NbofRooms != 0)
{
var apartment = await _context.Apartments.Where(s => s.NbofRooms == NbofRooms).OrderByDescending(s => s.Price).ToListAsync();
if (apartment == null)
{
return NotFound();
}
return Ok(apartment);
}
else
{
var apartment = _context.Apartments;
if (apartment == null)
{
return NotFound();
}
return Ok(apartment);
}
}
// PUT: api/Apartments/5
[HttpPut("{id}")]
public async Task<IActionResult> PutApartment([FromRoute] int id, [FromBody] Apartment apartment)
{
if (!ModelState.IsValid)
{
var errors = ModelState.Values.SelectMany(v => v.Errors);
return BadRequest(ModelState);
}
if (id != apartment.ID)
{
return BadRequest();
}
_context.Entry(apartment).State = EntityState.Modified;
try
{
await _context.SaveChangesAsync();
}
catch (DbUpdateConcurrencyException)
{
if (!ApartmentExists(id))
{
return NotFound();
}
else
{
throw;
}
}
return NoContent();
}
// POST: api/Apartments
[HttpPost]
public async Task<IActionResult> PostApartment([FromBody] Apartment apartment)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
_context.Apartments.Add(apartment);
await _context.SaveChangesAsync();
return CreatedAtAction("GetApartment", new { id = apartment.ID }, apartment);
}
// DELETE: api/Apartments/5
[HttpDelete("{id}")]
public async Task<IActionResult> DeleteApartment([FromRoute] int id)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
var apartment = await _context.Apartments.SingleOrDefaultAsync(m => m.ID == id);
if (apartment == null)
{
return NotFound();
}
_context.Apartments.Remove(apartment);
await _context.SaveChangesAsync();
return Ok(apartment);
}
private bool ApartmentExists(int id)
{
return _context.Apartments.Any(e => e.ID == id);
}
}
}
这是我的上下文类：
public class ApartmentContext: DbContext
{
public ApartmentContext(DbContextOptions options) : base(options)
{
}
protected override void OnModelCreating(ModelBuilder builder)
{
base.OnModelCreating(builder);
}
public DbSet<Apartment> Apartments { get; set; }
public DbSet<Buyer> Buyers { get; set; }
}
返回不止一个公寓的所有物品都无法正常工作。