LINQ to Entities 无法识别方法 'Int32 Int32(System.String)' 方法，并且此方法无法转换为存储表达式 [英] LINQ to Entities does not recognize the method 'Int32 Int32(System.String)' method, and this method cannot be translated into a store expression

问题描述

我正在尝试使用 Linq to Entities 查询数据库上下文，但出现此错误:

I am trying to Query Database Context using Linq to Entities and I am getting this error:

LINQ to Entities 无法识别方法 'Int32 Int32(System.String)' 方法，并且该方法无法转换为存储表达式.`

LINQ to Entities does not recognize the method 'Int32 Int32(System.String)' method, and this method cannot be translated into a store expression.`

代码:

public IEnumerable<CourseNames> GetCourseName()
{
   var course = from o in entities.UniversityCourses
                select new CourseNames
                {
                    CourseID = Convert.ToInt32(o.CourseID),
                    CourseName = o.CourseName,
                 };
   return course.ToList();
}

我在看到 这个

public IEnumerable<CourseNames> GetCourseName()
{
    var temp = Convert.ToInt32(o.CourseID);
    var course = from o in entities.UniversityCourses
                 select new CourseNames
                 {
                     CourseID = temp,
                     CourseName = o.CourseName,
                 };
    return course.ToList();
}

但它抛出一个错误:

当前上下文中不存在名称‘o’"

"The name 'o' does not exist in the current context"

这是我为 GetCourseName

namespace IronwoodWeb
{
    public class CourseNames
    {
        public int CourseID { get; set; }
        public string CourseName { get; set; }
    }
}

推荐答案

public IEnumerable<CourseNames> GetCourseName()
{
    var courses = from o in entities.UniversityCourses
                  select new { o.CourseID, o.CourseName };

    return courses.ToList() // now we have in-memory query
                  .Select(c => new CourseNames()
                  {
                     CourseID = Convert.ToInt32(c.CourseID), // OK
                     CourseName = c.CourseName
                  });
}

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