Question

我有以下一席和POCO班:

public enum Gender
{
    Male,
    Female,
    Unknown
}

public class Person
{
    public int PersonId { get; set; }
    public string LastName { get; set; }
    public string FirstName { get; set; }
    public Gender? Gender { get; set; }
}

我要在我的存放处进行“面向所有人”的问询,这样它就能够研究这样的问题:

return from p in _db.People
       select new Model.Person
       {
          PersonId = p.PersonId,
          LastName = p.LastName,
          FirstName = p.FirstName,
          Gender = p.Gender,
       };

不幸的是,我犯了一个错误,即“没有含蓄地将扼制为模型的类型转换成模型。两性平等

我愿将实体框架所编的插座改为我的性别系,并将其分配给我的组织。

Answer 1

在实体框架中,Enums没有得到支持。亚历克·詹姆斯进行了工作,但这项工作相当多。

相反,我更愿意这样做:

public enum Gender : byte
{
    Male = 1,
    Female,
    Unknown
}

public class Person
{
    public int PersonId { get; set; }
    public string LastName { get; set; }
    public string FirstName { get; set; }
    public byte Gender { get; set; } // this is the EF model property
    public Gender GenderType // this is an additional custom property
    { 
        get { return (Gender) Gender; }
        set { Gender = (byte)value; }
    }
}

它对实际价值来说基本上是一个 h/rap。在您的数据库中,将性别问题作为<代码>tinyint(在概念方面,将性别分布在byte上)。

之后,你可以使用星号绘制和从模型财产中取出:

return from p in _db.People
       select new Model.Person
       {
          PersonId = p.PersonId,
          LastName = p.LastName,
          FirstName = p.FirstName,
          Gender = p.Gender, // sets byte
       };

但是,如果你能够查阅这一观点,因为你为<代码>Gender确定了星号,那么你也将有机会查阅财产编码。

这是否解决了你的问题?

Answer 2

我所熟悉的实体框架没有为论坛提供支持。 EF利用你的问询,制作一份显示文件,然后发送给服务器,如果它不能建立某种操作的等同结构,它就会对这一行动不支持。如果您希望能够退还少量数据,你可以通过使用<代码>ToArray方法创建用于记忆的物体,与实体框架分开。

var myEntities = (from entity in _db.Entities
                  where /* condition */
                  select entity)
                        .ToArray();

This will create a sequence of entities in memory. Any further query statements will then be in the realm of LINQ to Objects which allows parsing of strings into enums:

return from myEntity in myEntities
       select new MyDataContract
       {
            ID = myEntity.ID,
            Gender g = (Gender)Enum.Parse(typeof(Gender), myEntity.Gender, true)
       };

或者,你甚至可以将其细分为<代码>foreach。住宿:

List<MyDataContract> myDataContracts = new List<MyDataContract>();
foreach (var myEntity in myEntities)
{
    var dataContract = new MyDataContract { ID = myEntity.ID };

    if (Enum.IsDefined(typeof(Gender), myEntity.Gender))
        dataContract.Gender = (Gender)Enum.Parse(typeof(Gender), myEntity.Gender, true);

        myDataContracts.Add(dataContract);
}

return myDataContracts.AsEnumerable();

Answer 3

   if (Enum.IsDefined(typeof(Gender), genderstring))
      Gender g = (Gender) Enum.Parse(typeof(Gender), genderstring, true);
   else
      //Deal with invalid string.

Answer 4

~~try~~

Gender = p.Gender != null ? (Gender)Enum.Parse(typeof(Gender), p.Gender) : (Gender?)null;

To parse the string as one of the enums

它意味着改变你的冰和干净的POCO

http://blogs.msdn.com/b/alexj/archive/2009/06/05/tip-23-how-to-fake-enums-in-ef-4.aspx”rel=“nofollow”http://blogs.msdn.com/b/alexj/archive/2009/06/05/tip-23-how-to-fake-enums-in-ef-4.aspx

友情链接