InheritanceMappingAttribute Class

Definition

Namespace:

System.Data.Linq.Mapping

Assembly:

System.Data.Linq.dll

Maps an inheritance hierarchy in a LINQ to SQL application.

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

Inheritance

Object

Attribute

InheritanceMappingAttribute

Attributes

AttributeUsageAttribute

Examples

This example shows inheritance mapping for a hierarchy where the top, mapped class (Shape) is abstract.

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

The following example shows the inclusion of unmapped classes. You can put unmapped classes anywhere in the hierarchy.

// 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

Remarks

One InheritanceMappingAttribute is specified per mapped class.

Note the following when you map inheritance hierarchies:

• All classes in a hierarchy must be mapped to a single table.

• The table for an inheritance hierarchy must be declared on the mapped type that is at the top of the hierarchy. You cannot specify the table or mapping attributes in a class that is derived from the top class.

• You can use an interface in a hierarchy, but LINQ does not map it.

• You can skip a class in the hierarchy when you map classes, but you can query against mapped classes only.

For correct materialization, discriminator code values must be unique and match the values in the database. A row with a discriminator code value that does not exactly match (even by casing) instantiates the class by using IsDefault set to true.

Constructors

InheritanceMappingAttribute()

Initializes a new instance of the InheritanceMappingAttribute class.

Properties

Code	Gets or sets the discriminator code value in a mapped inheritance hierarchy.
IsDefault	Gets or sets whether an object of this type in instantiated when the discriminator value does not match a specified value.
Type	Gets or sets the type of the class in the hierarchy.
TypeId	When implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute)

Methods

Equals(Object)	Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute)
GetHashCode()	Returns the hash code for this instance. (Inherited from Attribute)
GetType()	Gets the Type of the current instance. (Inherited from Object)
IsDefaultAttribute()	When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute)
Match(Object)	When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)

Explicit Interface Implementations

_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)	Maps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute)
_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)	Retrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute)
_Attribute.GetTypeInfoCount(UInt32)	Retrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute)
_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)	Provides access to properties and methods exposed by an object. (Inherited from Attribute)