这是我的错误消息:'IEnumerable'不包含'FirstOrDefaultAsync'的定义,并且没有可访问的扩展方法'FirstOrDefaultAsync'接受类型'IEnumerable'的第一个参数可以找到(你是否缺少using指令或程序集引用? )
我已完成以下操作并且错误仍然存在:
这是我的.cshtml.cs代码,其中生成错误(第34行):
DbSet doesn't contain definition for FirstOrDefault?
这是我的DataAccessLayer,它由上面的代码引用并返回IEnumerable。
using System.Collections.Generic;
using System.Linq;
using System.Data.Entity;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.EntityFrameworkCore;
using Movies.Models;
namespace Movies.Pages.MediaDetails
{
public class DetailsModel : PageModel
{
private readonly Movies.Models.MoviesContext _context;
public DetailsModel(Movies.Models.MoviesContext context)
{
_context = context;
}
MovieDataAccessLayer objmovie = new MovieDataAccessLayer();
public Movies Movies { get; set; }
public async Task<IActionResult> OnGetAsync(byte? id)
{
if (id == null)
{
return NotFound();
}
Movies = await objmovie.MovieByMedia(id).FirstOrDefaultAsync(m => m.MediaTypeID == id);
if (Movies == null)
{
return NotFound();
}
return Page();
}
}
}
任何输入将不胜感激。
using System.ComponentModel.DataAnnotations;
using System.Data;
using System.Data.Entity;
using System.Data.SqlClient;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
namespace Movies.Models
{
public class MovieDataAccessLayer
{
string connectionString = "Server=servername;Database=DatabaseMovies;Trusted_Connection=True;MultipleActiveResultSets=true";
public IEnumerable<Movies> MovieByMedia(byte? MediaID)
{
List<Movies> lstmovie = new List<Movies>();
using (SqlConnection con = new SqlConnection(connectionString))
{
SqlCommand cmd = new SqlCommand("usp_MovieByMedia", con);
cmd.Parameters.Add(new SqlParameter("@MediaID", SqlDbType.TinyInt) { Value = MediaID });
cmd.CommandType = CommandType.StoredProcedure;
con.Open();
SqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
Movies movies = new Movies();
movies.MovieTitle = rdr["MovieTitle"].ToString();
movies.MovieYear = Convert.ToInt32(rdr["MovieYear"]);
lstmovie.Add(movies);
}
con.Close();
}
return lstmovie;
}
}
}
方法是IQueryable接口上的扩展方法。由于您的数据访问方法返回IEnumerable而不是异步,因此您应该使用.FirstOrDefaultAsync()
。
.FirstOrDefault()
尝试将您的IEnumerable转换为某种实际的集合,例如:
https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.firstordefault?view=netframework-4.8