InheritanceMappingAttribute 類別

定義

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

繼承

Object

Attribute

InheritanceMappingAttribute

屬性

AttributeUsageAttribute

範例

此範例展示了階層結構中頂端映射類別（Shape）為抽象的繼承映射。

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

以下範例展示了未映射類別的包含。 你可以把未映射的類別放在階層結構的任何位置。

// 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

備註

每個映射類別會指定一個 InheritanceMappingAttribute 。

當你繪製繼承階層時，請注意以下幾點：

• 階層中的所有類別必須映射到單一資料表。

• 繼承階層的表格必須在階層頂端的映射型別上宣告。 你無法在從頂層類別衍生出的類別中指定表格或映射屬性。

• 你可以在階層結構中使用介面，但 LINQ 不會映射它。

• 你可以在映射類別時跳過階層中的一個類別，但只能查詢映射過的類別。

為了正確的物質化，判別碼值必須是唯一且與資料庫中的值相符的。 若一列判別子代碼值不完全匹配（即使大小寫）則透過 set 到 true來實例化該類別IsDefault。