Question

我创建了一个JoinModel类来连接多个表的课程列表，即Model文件夹下的课程摘要。以前工作正常。现在，我添加了一个包含新年，课程表2019的表格，并将课程表2019添加到CourseDateModel.cs中。但是我收到错误消息，抱怨“无法在LINQ to Entities查询中构造”。我正在使用Entity Framework 6，首先使用代码生成CourseDataModel.cs文件。下面是我的代码：

CourseDataModel.cs

namespace course.Models
{
using System;
using System.Data.Entity;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;

public partial class CourseDataModel : DbContext
{
    public CourseDataModel()
        : base("name=CourseDataModel")
    {
    }


    public virtual DbSet<courselist> courselist { get; set; 
    public virtual DbSet<courselist2019> courselist2019 { get; set; }
    public virtual DbSet<contentsummary> contentsummary { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {

    }
}
}

JoinModel.cs

public class JoinModel
{
    [Key]
    public int id { get; set; }
    public contentsummary Contentsummary { get; set; }
    public courselist Courselist { get; set; }
    public courselist2019 Courselist2019 { get; set; }
}

HomeController.cs

 public ActionResult Index( )
        {

    var searchResults = (from a in db.courselist
                 join b in db.coursesummary on
                                new { subject=a.subject, catalog=a.catalog    } equals
                                 new { subject=b.Subject,   catalog=b.Catalogno } into ab
                                 where a.active ==true
                                 from b in ab.DefaultIfEmpty()

                                 select new JoinModel
                                 {
                                     Courselist = a,
                                     Contentsummary = b


                                 }).ToList();
return View(searchResults);
}

我尝试更改查询

var searchResults = (from a in db.courselist
                 join b in db.coursesummary on
                                new { subject=a.subject, catalog=a.catalog } equals
                                 new { subject=b.Subject, catalog=b.Catalogno } into ab
                                 where a.active ==true
                                 from b in ab.DefaultIfEmpty()

                                 //select new JoinModel
                                  select new
                                 {
                                     Courselist = a,
                                     Contentsummary = b


                                 }).ToList()
                                 .Select(x=>new JoinModel(){Courselist=x.a, Contentsummary=x.b});

Answer 1

我发现CourseDataModel.cs文件包含系统生成的额外代码行。我注释掉了，现在可以正常工作：

//public System.Data.Entity.DbSet<course.Models.JoinModel2019> JoinModel2019 { get; set; }

在DataModel中添加新表时的LINQ to Entities查询

1 个答案: