c# - 在 Entity Framework 中为某些参数排序

Question

我有一个搜索结果表，其中有一个包含有限值的列

"Completed", "Recruiting", "Active and not Recruiting" 

我希望“Recruiting”行排在第一位，然后是“Active and not Recruiting”，最后是“Completed”。

我正在使用的表达式是这样的

List<Search> lst = new List<Search>(); 

var hello = db.tblSomething.Where(em=>em.someid==obj.someid).ToList

foreach(item in hello)
{
   SomeClass obj1 = new SomeClass();
   obj1.Status = hello.Status;   
   lst.Add(obj1);   
}

Status 可以包含“Completed”、“Recruiting”、“Active and not Recruiting”三个中的任何一个。

Recruiting Status 元素首先出现的表达式是什么？

Answer 1

I want "Recruiting" columns to come first and then "Active and not Recruiting" and at last "Completed".

使用OrderBy .

DotNetFiddle Example .

    public static void Main()
{
    var list = new List<SomeClass>
    {
        new SomeClass{ Status = "Recruiting"},
        new SomeClass{ Status = "Completed"},
        new SomeClass{ Status = "Active and not Recruiting"},
        new SomeClass{ Status = "Completed"},
        new SomeClass{ Status = "Recruiting"}
    };
    
    PrintList(list);
    
    Console.WriteLine("-");
    
    var sorted = list
        .OrderBy(sc => sc.Status.Equals("Recruiting", StringComparison.OrdinalIgnoreCase)
            ? 0
            : sc.Status.Equals("Active and not Recruiting", StringComparison.OrdinalIgnoreCase)
                 ? 1
                 : sc.Status.Equals("Completed", StringComparison.OrdinalIgnoreCase)
                    ? 2
                    : 3)
        .ToList();
    
    
    PrintList(sorted);

}

public static void PrintList(IEnumerable<SomeClass> list)
{
    foreach(var sc in list) Console.WriteLine(sc.Status);
}

public class SomeClass
{
    public string Status { get; set; }  
}

结果:

Recuiting

Completed

Active and not Recruiting

Completed

Recuiting

-

Recuiting

Recuiting

Active and not Recruiting

Completed

Completed

这一切都很好，但代码非常丑陋且非常脆弱。相反，我强烈建议使用 Enum和 DisplayAttribute .

DotNetFiddle Example

using System;
using System.Linq;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
                    
public class Program
{
    public enum StatusType
    {
        [Display(Name = "Invalid", Order = -1)]
        Invalid = 0,
        [Display(Name = "Recuiting", Order = 0)]
        Recruiting,
        [Display(Name = "Completed", Order = 2)]
        Completed,
        [Display(Name = "Active and not Recruiting", Order = 1)]
        ActiveAndNotRecruiting
    }
    
    
    public static void Main()
    {
        var list = new List<SomeClass>
        {
            new SomeClass{ Status = StatusType.Recruiting, Id = 1, Name = "Abraham"},
            new SomeClass{ Status = StatusType.Completed, Id = 2, Name = "Ben"},
            new SomeClass{ Status = StatusType.ActiveAndNotRecruiting, Id = 3, Name = "Carl"},
            new SomeClass{ Status = StatusType.Completed, Id = 4, Name = "Dan"},
            new SomeClass{ Status = StatusType.Recruiting, Id = 5, Name = "Erin"}
        };
        
        PrintList(list);
        
        Console.WriteLine("-");
        
        var sorted = list
            .OrderBy(cs => cs.Status.ToDisplay().Order)
            .ToList();
        
        
        PrintList(sorted);

    }

    public static void PrintList(IEnumerable<SomeClass> list)
    {
        foreach(var sc in list) Console.WriteLine("{0}, {1} is {2}", sc.Id, sc.Name, sc.Status.ToDisplay().Name);
    }
    
    public class SomeClass
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public StatusType Status { get; set; }  
    }
}

public static class EnumExtensions
{
    public static DisplayAttribute ToDisplay(this Enum enumValue) 
    {
        return enumValue.GetType()
            .GetMember(enumValue.ToString())
            .First()
            .GetCustomAttributes(false)
            .Where(a => a is DisplayAttribute)
            .FirstOrDefault() as DisplayAttribute;
    }
}

结果:

1, Abraham is Recuiting

2, Ben is Completed

3, Carl is Active and not Recruiting

4, Dan is Completed

5, Erin is Recuiting

-

1, Abraham is Recuiting

5, Erin is Recuiting

3, Carl is Active and not Recruiting

2, Ben is Completed

4, Dan is Completed

使用枚举的优点是属性的名称和排序被封装到一个逻辑位置。如果你想改变顺序，你可以在一个地方这样做，确保其他一切都改变并且没有其他东西会中断。这也删除了 magic numbers/strings 的使用.