第一个具有继承TPH的复杂类型

Question

是否可以在EF 4.1中使用复杂类型的继承TPH ?

    [ComplexType]
    public class Unit
    {
        public double Value { get; set; }
        public Unit() { }
        public Unit(double Value)
        {
            this.Value = Value;
        }
    }
    public class Celsius: Unit
    {
       public Celsius(double Value) : base (Value)  { }
       public static explicit operator Kelvin(Celsius c)
       {
         return new Kelvin(c.Degrees + 273.16d);
       }
       [NotMapped]
       public double Degrees 
       {
         get { return this.Value; }
       }
    }

我在这个类关联中使用一对一:当我调用()SaveChanges()引发异常

public class Measurement
{
    [Key,
     Column("Id"),
     DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long Id { get; set; }
    public DateTime MTime { get; set; }
    public Unit Value { get; set; }
}

和上下文:

class TestContext : DbContext
{
    public DbSet<Measurement> Measurements { get; set; }
    protected override void OnModelCreating(DbModelBuilder modelBuilder)     
    {
        try
        {
            modelBuilder.ComplexType<Unit>().Property(u => u.Value).HasColumnName("Value");
            modelBuilder.Entity<Unit>()
                        .Map<Celsius>(m => m.Requires("TypeName").HasValue("Celsius"))
                        .Map<Kelvin>(m => m.Requires("TypeName").HasValue("Kelvin"));
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex);
        }
    } 
}

是否有可能在FE 4.1代码中首先使用具有继承的单表层次结构的复杂类型?

Answer 1

好的，我在EF 5 beta测试，但我认为这应该是一样的。这是一种变通方法，但你可能能够接受。当这是一个复杂类型时，鉴别符部分似乎不起作用，所以我在各自的构造函数中初始化了它。

我有这个，它工作:

public class Measurement
{
    [Key,
        Column("Id"),
        DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long Id { get; set; }
    public DateTime MTime { get; set; }
    public virtual Unit Value { get; set; }
}
[ComplexType]
public class Unit
{
    protected Unit()
    {
    }
    protected Unit(double value)
    {
        Value = value;
    }
    [Column("Value")]
    public double Value { get; set; }
    [Column("TypeName")]
    public string TypeName { get; set; }
}
public class Celsius : Unit
{
    public Celsius(double value) : base(value)
    {
        TypeName = "Celsius";
    }
    public static explicit operator Kelvin(Celsius c)
    {
        return new Kelvin(c.Degrees + 273.16d);
    }
    public double Degrees
    {
        get { return this.Value; }
    }
}
public class Kelvin : Unit
{
    public Kelvin(double value) : base(value)
    {
        TypeName = "Kelvin";
    }
    public static explicit operator Celsius(Kelvin k)
    {
        return new Celsius(k.Degrees - 273.16d);
    }
    public double Degrees
    {
        get { return this.Value; }
    }
}
class TestContext : DbContext
{
    public DbSet<Measurement> Measurements { get; set; }
}

下面是它的迁移代码，以查看在DB中生成的内容:

public partial class Initial : DbMigration
{
    public override void Up()
    {
        CreateTable(
            "dbo.Measurements",
            c => new
                {
                    Id = c.Long(nullable: false, identity: true),
                    MTime = c.DateTime(nullable: false),
                    Value = c.Double(nullable: false),
                    TypeName = c.String(),
                })
            .PrimaryKey(t => t.Id);
    }
    public override void Down()
    {
        DropTable("dbo.Measurements");
    }
}