作为枚举类属性 [英] Enum as Class Property
问题描述
我有一类简单的东西,状态,它包含两个属性。我想用一个枚举的属性(StatusID)中的一个,这样我可以消灭一堆魔字符串。
我的问题是,再怎么我使用它,比如:我有一个方法,该方法返回一个列表在一个下拉框,看起来像这样绑定 - >
公共静态的IList<状态> GetAdminStatuses()
{
IQueryable的<状态> STAT = context.tblAdminStatus
。凡(S => s.InactiveDate> DateTime.Now || s.InactiveDate == NULL)
。选择(S =>新建状态()
{
StatusID = s.StatusID,
状态说明= s.StatusDesc
});
返回stat.ToList();
}
这显然不喜欢我的 StatusID = s.StatusID
部分为DB将它存储为VARCHAR。我失去了一些简单的在这里还是有我偶然到小白的领土,不应该做这种方式?
有关参考这里是类和枚举:
公共类状态
{
公共字符串StatusID {获得;组;}
公共字符串状态说明{获得;组;}
}
公共枚举MyStatusID
{
草案,以待,拒绝,接受,关闭
}
修改
因此,采取的意见在这里我能得到我的方法但是编译在运行时我得到以下 - > 法System.Object的解析(System.Type的,System.String)有不支持转换为SQL。
思考?
编辑 - 它的方法是全部按要求,谢谢(请注意,NoaStatusID == MyStatusID)
公共静态的IList<状态> GetAdminStatuses(NoaStatusID currentStatus = NoaStatusID.draft)
{
使用(VAR上下文= MemberDataContext.Create())
{
IQueryable的<状态> STAT = context.tblAdminStatus
。凡(S => s.InactiveDate> DateTime.Now || s.InactiveDate == NULL)
。选择(S =>新建状态()
{
StatusID = NoaStatusID)Enum.Parse(typeof运算(NoaStatusID),s.StatusID)
状态说明= s.StatusDesc
});
开关(currentStatus)
{
案例NoaStatusID.draft:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending));
打破;
案例NoaStatusID.pending:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.accepted || s.StatusID == NoaStatusID.declined || s.StatusID == NoaStatusID.pending));
打破;
案例NoaStatusID.declined:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending || s.StatusID == NoaStatusID.declined));
打破;
案例NoaStatusID.accepted:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.accepted) );
打破;
案例NoaStatusID.mailed:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal) );
打破;
案例NoaStatusID.monitor:
案例NoaStatusID.appeal:
案例NoaStatusID.close:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal));
打破;
}
返回stat.ToList();
}
}
我相信你正在寻找的是:
StatusID =(MyStatusID)Enum.Parse(typeof运算(MyStatusID),s.StatusID)
在.NET 4.0中也有一个 Enum.TryParse(字符串,出枚举)
但是这不是你的。选择里面非常有用( )
或者
尽管在大多数情况下效率不高,你可以保持 Status.StatusID
作为一个字符串,并添加只读属性 StatusEnum
的飞输出枚举值:
公共MyStatusID StatusEnum {
得到 {
返程(MyStatusID)Enum.Parse(typeof运算(MyStatusID),StatusID)
}
私定;
}
在.NET 4.0中:
公共MyStatusID StatusEnum {
得到 {
MyStatusID值;
如果(!Enum.TryParse(StatusID,超时值)
值= MyStatusID.Default; //默认值,而不是异常投掷
返回值;
}
私定;
}
这种替代重新解析值每次instance.StatusEnum被读取,所以我不建议这样做,除非LINQ恨第一种方法
在回答你的最后编辑:
在Enum.Parse()被翻译成SQL罚款,你的榜样。问题出在哪里,你要添加一个。凡()
子句具有与枚举$ C $比较switch语句C>。 LINQ不知道如何把一个
枚举==枚举
成SQL,但它的确实知道用C#对象做到这一点。因此最简单的解决办法就是了ToList()他们,并做局部的比较。不幸的是,这意味着它的下载行从数据库中-all-状态类型,然后在本地过滤它们。如果你有百万条记录这未必是合理的:
公共静态的IList<状态> GetAdminStatuses(NoaStatusID currentStatus = NoaStatusID.draft)
{
使用(VAR上下文= MemberDataContext.Create())
{
名单<状态> STAT = context.tblAdminStatus
。凡(S => s.InactiveDate> DateTime.Now || s.InactiveDate == NULL)
。选择(S =>新建状态()
{
StatusID = NoaStatusID)Enum.Parse(typeof运算(NoaStatusID),s.StatusID)
状态说明= s.StatusDesc
})
.ToList();
开关(currentStatus)
{
案例NoaStatusID.draft:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending))了ToList()。
打破;
案例NoaStatusID.pending:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.accepted || s.StatusID == NoaStatusID.declined || s.StatusID == NoaStatusID.pending))了ToList()。
打破;
案例NoaStatusID.declined:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending || s.StatusID == NoaStatusID.declined))了ToList()。
打破;
案例NoaStatusID.accepted:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.accepted) ).ToList();
打破;
案例NoaStatusID.mailed:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal) ).ToList();
打破;
案例NoaStatusID.monitor:
案例NoaStatusID.appeal:
案例NoaStatusID.close:
STAT = stat.Where(S =>(s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal))了ToList()。
打破;
}
返回统计;
}
}
I have a class for something simple, Status, and it contains two properties. I want to use an Enum for one of the Properties(StatusID) so that I can eliminate a bunch of Magic Strings.
My question is how I then work with it, for example: I have a Method that returns a List for binding in a dropdown box that looks like this -->
public static IList<Status> GetAdminStatuses()
{
IQueryable<Status> stat=context.tblAdminStatus
.Where(s => s.InactiveDate > DateTime.Now || s.InactiveDate == null)
.Select(s => new Status()
{
StatusID=s.StatusID,
StatusDescription=s.StatusDesc
});
return stat.ToList();
}
It obviously does not like my StatusID=s.StatusID
part as the DB stores it as a varchar. Am I missing something simple here or have I stumbled into noob territory and should not be doing it this way?
For reference here is the Class and Enum:
public class Status
{
public string StatusID {get; set;}
public string StatusDescription {get; set;}
}
public enum MyStatusID
{
draft, pending, declined, accepted, close
}
EDIT
So taking the advice here I was able to get my method to compile however at runtime I get the following --> Method 'System.Object Parse(System.Type, System.String)' has no supported translation to SQL.
Thoughts?
EDIT - Method in it's entirety by request, thanks (NOTE that NoaStatusID == MyStatusID)
public static IList<Status> GetAdminStatuses(NoaStatusID currentStatus = NoaStatusID.draft)
{
using (var context = MemberDataContext.Create())
{
IQueryable<Status> stat=context.tblAdminStatus
.Where(s => s.InactiveDate > DateTime.Now || s.InactiveDate == null)
.Select(s => new Status()
{
StatusID=NoaStatusID)Enum.Parse(typeof(NoaStatusID),s.StatusID),
StatusDescription=s.StatusDesc
});
switch (currentStatus)
{
case NoaStatusID.draft:
stat=stat.Where(s => (s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending));
break;
case NoaStatusID.pending:
stat = stat.Where(s => (s.StatusID == NoaStatusID.accepted || s.StatusID ==NoaStatusID.declined || s.StatusID ==NoaStatusID.pending));
break;
case NoaStatusID.declined:
stat = stat.Where(s => (s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending || s.StatusID == NoaStatusID.declined));
break;
case NoaStatusID.accepted:
stat = stat.Where(s => (s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.accepted));
break;
case NoaStatusID.mailed:
stat = stat.Where(s => (s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal));
break;
case NoaStatusID.monitor:
case NoaStatusID.appeal:
case NoaStatusID.close:
stat = stat.Where(s => (s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal));
break;
}
return stat.ToList();
}
}
i believe what you're searching for is:
StatusID = (MyStatusID)Enum.Parse(typeof(MyStatusID), s.StatusID),
in .Net 4.0 there is also a Enum.TryParse(string, out enum)
but that is not so useful inside your .Select()
Alternatively:
albeit less efficient in most cases, you can keep the Status.StatusID
as a string and add a readonly property StatusEnum
that outputs the Enum value on the fly:
public MyStatusID StatusEnum {
get {
return (MyStatusID)Enum.Parse(typeof(MyStatusID), StatusID)
}
private set;
}
in .Net 4.0:
public MyStatusID StatusEnum {
get {
MyStatusID value;
if(!Enum.TryParse(StatusID, out value)
value = MyStatusID.Default; // default value, instead of Exception throwing
return value;
}
private set;
}
this alternative re-parses the value everytime instance.StatusEnum is read, so I don't recommend it unless LINQ hates the first approach
Responding to your last EDIT:
The Enum.Parse() is translating to SQL fine in your example. The problem is in the switch statement where you're adding on a .Where()
clause that has a comparison with an Enum
. LINQ doesn't know how to turn an Enum == Enum
into SQL but it does know to do it with C# objects. So the easiest solution is to ToList() them and do the comparison locally. Unfortunately, that means it's downloading rows of -all- Status types from the database and then filters them locally. If you have millions of records this may not be reasonable:
public static IList<Status> GetAdminStatuses(NoaStatusID currentStatus = NoaStatusID.draft)
{
using (var context = MemberDataContext.Create())
{
List<Status> stat=context.tblAdminStatus
.Where(s => s.InactiveDate > DateTime.Now || s.InactiveDate == null)
.Select(s => new Status()
{
StatusID=NoaStatusID)Enum.Parse(typeof(NoaStatusID),s.StatusID),
StatusDescription=s.StatusDesc
})
.ToList();
switch (currentStatus)
{
case NoaStatusID.draft:
stat=stat.Where(s => (s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending)).ToList();
break;
case NoaStatusID.pending:
stat = stat.Where(s => (s.StatusID == NoaStatusID.accepted || s.StatusID ==NoaStatusID.declined || s.StatusID ==NoaStatusID.pending)).ToList();
break;
case NoaStatusID.declined:
stat = stat.Where(s => (s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending || s.StatusID == NoaStatusID.declined)).ToList();
break;
case NoaStatusID.accepted:
stat = stat.Where(s => (s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.accepted)).ToList();
break;
case NoaStatusID.mailed:
stat = stat.Where(s => (s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal)).ToList();
break;
case NoaStatusID.monitor:
case NoaStatusID.appeal:
case NoaStatusID.close:
stat = stat.Where(s => (s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal)).ToList();
break;
}
return stat;
}
}
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