一个枚举值存储的问题详解编程语言

枚举是编程中常见的类型，经常在代码中使用。枚举的好处就不说了，需要注意的一点是在编译时会变成静态int。这个地方需要注意一下，不然会出现问题。

如下代码定义枚举，并把数据存储到数据库中。

using System; 
using System.Linq; 
using Wisdombud.Mongo; 
namespace MongoTest 
{ 
    public class MongoEnumTest 
    { 
        private MongoDbBaseDao<MyEnum> dao = new MongoDbBaseDao<MyEnum>("mongodb://192.168.163.36:27017/chzhaotest"); 
        public void Test() 
        { 
            MyEnum me1 = new MyEnum(); 
            me1.Name = "company1"; 
            me1.WorkDay = Days.Mon; 
            MyEnum me2 = new MyEnum(); 
            me2.Name = "company2"; 
            me2.WorkDay = Days.Fri; 
            this.dao.Save(me1); 
            this.dao.Save(me2); 
            MyEnum me3 = this.dao.GetAll().ToList().First(); 
            Console.WriteLine(me3.WorkDay + me3.Name); 
        } 
    } 
    public enum Days { Mon, Tue, Wed, Thu, Fri }; 
    public class MyEnum : Wisdombud.Mongo.MongoDbEntity 
    { 
        public string Name { get; set; } 
        public Days WorkDay { get; set; } 
    } 
} 

数据存储到数据库中是这样的[mongodb]。

/* 0 */ 
{ 
  "_id" : ObjectId("551d0ce1b15ae72abc8b42e9"), 
  "Name" : "company1", 
  "WorkDay" : 0 
} 
 
/* 1 */ 
{ 
  "_id" : ObjectId("551d0ce2b15ae72abc8b42ea"), 
  "Name" : "company2", 
  "WorkDay" : 4 
} 
 

如上代码运行结果的是

Moncompany1 

可是如果我要增加枚举的类型，改成如下代码。

using System; 
using System.Linq; 
using Wisdombud.Mongo; 
namespace MongoTest 
{ 
    public class MongoEnumTest 
    { 
        private MongoDbBaseDao<MyEnum> dao = new MongoDbBaseDao<MyEnum>("mongodb://192.168.163.36:27017/chzhaotest"); 
        public void Test() 
        { 
            MyEnum me1 = new MyEnum(); 
            me1.Name = "company1"; 
            me1.WorkDay = Days.Mon; 
            MyEnum me2 = new MyEnum(); 
            me2.Name = "company2"; 
            me2.WorkDay = Days.Fri; 
            this.dao.Save(me1); 
            this.dao.Save(me2); 
            MyEnum me3 = this.dao.GetAll().ToList().First(); 
            Console.WriteLine(me3.WorkDay + me3.Name); 
        } 
    } 
    public enum Days { Sta, Sun, Mon, Tue, Wed, Thu, Fri }; 
    public class MyEnum : Wisdombud.Mongo.MongoDbEntity 
    { 
        public string Name { get; set; } 
        public Days WorkDay { get; set; } 
    } 
} 

注意，我在Mon前面增加了Sta和Sun。在数据库中存储的是

/* 0 */ 
{ 
  "_id" : ObjectId("551d0ce1b15ae72abc8b42e9"), 
  "Name" : "company1", 
  "WorkDay" : 0 
} 
 
/* 1 */ 
{ 
  "_id" : ObjectId("551d0ce2b15ae72abc8b42ea"), 
  "Name" : "company2", 
  "WorkDay" : 4 
} 
 
/* 2 */ 
{ 
  "_id" : ObjectId("551d0dc1b15ae722cce4af5f"), 
  "Name" : "company1", 
  "WorkDay" : 2 
} 
 
/* 3 */ 
{ 
  "_id" : ObjectId("551d0dc2b15ae722cce4af60"), 
  "Name" : "company2", 
  "WorkDay" : 6 
} 
 

两条新的数据变成了2和6，而不是0和4，也就说，当我在前面增加了新的类型之后，所有的枚举都乱了，而且数据库中存储的也错误了。一切原因都是在编译时会变成静态int*

解决这个问题的办法也很简单，在定义枚举时给枚举赋一个默认值，但要从0开始，如下：

using System; 
using System.Linq; 
using Wisdombud.Mongo; 
namespace MongoTest 
{ 
    public class MongoEnumTest 
    { 
        private MongoDbBaseDao<MyEnum> dao = new MongoDbBaseDao<MyEnum>("mongodb://192.168.163.36:27017/chzhaotest"); 
        public void Test() 
        { 
            MyEnum me1 = new MyEnum(); 
            me1.Name = "company1"; 
            me1.WorkDay = Days.Mon; 
            MyEnum me2 = new MyEnum(); 
            me2.Name = "company2"; 
            me2.WorkDay = Days.Fri; 
            this.dao.Save(me1); 
            this.dao.Save(me2); 
            MyEnum me3 = this.dao.GetAll().ToList().First(); 
            Console.WriteLine(me3.WorkDay + me3.Name); 
        } 
    } 
    public enum Days { Sta = 5, Sun = 6, Mon = 0, Tue = 1, Wed = 2, Thu = 3, Fri = 4 }; 
    public class MyEnum : Wisdombud.Mongo.MongoDbEntity 
    { 
        public string Name { get; set; } 
        public Days WorkDay { get; set; } 
    } 
}