c# - Entity Framework : OrderBy() numeric property when mapped column type is textual

Question

 return JsonConvert.SerializeObject(new Entities()
   .Student_Master
   .Where(k => k.Student_Location == Location && k.Student_Course == Program)
   .OrderBy(i => i.Student_Batch)
   .Select(i => i.Student_Batch)
   .Distinct()
   .ToList());

输出:

 [23,24,28,25,30,26,27,29]

需要输出

 [23,24,25,26,27,28,29,30]

我尝试使用 OrderBy(i => i.Student_Batch) 但在数据库中 Student_Batch 数据类型是 string 所以排序不正确

我试过如下

  var data=new Entities().Student_Master.Where(k => k.Student_Location == Location && k.Student_Course == Program).OrderBy(i => i.Student_Batch).Select(i => i.Student_Batch).Distinct().ToList();
 foreach(var obj in data)
   {
     //converted string to int then store in array 
   }

有什么简单的方法吗？

Answer 1

好的，因为问题出在排序上。您的选择很少，我将展示其中的 2 个。首先是您可以使用 Array.Sort()，这很常见:

string[] values = new Entities()
    .Student_Master
    .Where(k => k.Student_Location == Location && k.Student_Course == Program).Select(i => i.Student_Batch)
    .Distinct().ToArray();
Array.Sort(values); // all you need.

第二种常见方法是创建自定义比较器并在 OrderBy 中使用它:

public class MeComparer : IComparer<string> {
    public int Compare(string stringA, string stringB) {
        // your compare logic goes here...
        // eg. return int.Parse(stringA) - int.Parse(stringB)
    }
}

// and use it like 
return JsonConvert.SerializeObject(new Entities()
    .Student_Master
    .Where(k => k.Student_Location == Location && k.Student_Course == Program)
   .Select(i => i.Student_Batch)
   .Distinct()
   .ToList()
   .OrderBy(i => i.Student_Batch, new MeComparer()) // <-- HERE
);