InheritanceMappingAttribute 类

定义

public ref class InheritanceMappingAttribute sealed : Attribute

[System.AttributeUsage(System.AttributeTargets.Class, AllowMultiple=true, Inherited=false)]
public sealed class InheritanceMappingAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Class, AllowMultiple=true, Inherited=false)>]
type InheritanceMappingAttribute = class
    inherit Attribute

Public NotInheritable Class InheritanceMappingAttribute
Inherits Attribute

继承

Object

Attribute

InheritanceMappingAttribute

属性

AttributeUsageAttribute

示例

此示例演示层次结构的继承映射，其中顶层映射类 (Shape) 是抽象的。

public enum ShapeType
{
    Square = 0, Circle = 1
}
[Table(Name = "Shape")]
[InheritanceMapping(Code = ShapeType.Square, Type = typeof(Square),
    IsDefault = true)]
[InheritanceMapping(Code = ShapeType.Circle, Type = typeof(Circle))]

abstract public class Shape
{
    [Column(IsDiscriminator = true)]
    public ShapeType ShapeType = 0;
}

public class Square : Shape
{
    [Column]
    public int Side = 0;
}
public class Circle : Shape
{
    [Column]
    public int Radius = 0;
}

Public Enum ShapeType As Integer
    Square = 0
    Circle = 1
End Enum

<Table(Name:="Shape")> _
<InheritanceMapping(Code:=ShapeType.Square, Type:=GetType(Square), _
    IsDefault:=True)> _
<InheritanceMapping(Code:=ShapeType.Circle, Type:=GetType(Circle))> _
Public MustInherit Class Shape
    <Column(IsDiscriminator:=True)> _
        Public ShapeType As ShapeType = 0
End Class

Public Class Square
    Inherits Shape
    <Column()> _
    Public Side As Integer = 0
End Class

Public Class Circle
    Inherits Shape
    <Column()> _
    Public Radius As Integer = 0
End Class

以下示例演示如何包含未映射的类。 可以将未映射的类放在层次结构中的任意位置。

// Unmapped and not queryable.
class A {  }

// Mapped and queryable.
[Table]
[InheritanceMapping(Code = "B", Type = typeof(B),
IsDefault = true)]
[InheritanceMapping(Code = "D", Type = typeof(D))]
class B: A {  }

// Unmapped and not queryable.
class C: B {  }

// Mapped and queryable.
class D: C {  }

// Unmapped and not queryable.
class E: D {  }

' Unmapped and not queryable.
Class A
End Class

' Mapped and queryable.
<Table()> _
<InheritanceMapping(Code:="B", Type:=GetType(B), _
IsDefault:=True)> _
<InheritanceMapping(Code:="D", Type:=GetType(D))> _
Class B
    Inherits A
End Class

' Unmapped and not queryable.
Class C
    Inherits B
End Class

' Mapped and queryable.
Class D
    Inherits C
End Class

' Unmapped and not queryable.
Class E
    Inherits D
End Class

注解

每个映射类指定一个 InheritanceMappingAttribute 。

映射继承层次结构时，请注意以下事项：

• 层次结构中的所有类都必须映射到单个表。

• 继承层次结构的表必须在层次结构顶部的映射类型上声明。 不能在派生自顶级类的类中指定表或映射属性。

• 可以在层次结构中使用接口，但 LINQ 不会映射它。

• 映射类时，可以跳过层次结构中的类，但只能针对映射的类进行查询。

为了正确具体化，鉴别器代码值必须唯一且与数据库中的值匹配。 具有不完全匹配 (的鉴别器代码值的行，即使通过将大小写) 使用 IsDefault 设置为 true来实例化类。