DataObjectFieldAttribute Class

Definition

Namespace:

System.ComponentModel

Assembly:

System.ComponentModel.TypeConverter.dll

Source:

DataObjectFieldAttribute.cs

Provides metadata for a property representing a data field. This class cannot be inherited.

public ref class DataObjectFieldAttribute sealed : Attribute

[System.AttributeUsage(System.AttributeTargets.Property)]
public sealed class DataObjectFieldAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Property)>]
type DataObjectFieldAttribute = class
    inherit Attribute

Public NotInheritable Class DataObjectFieldAttribute
Inherits Attribute

Inheritance

Object

Attribute

DataObjectFieldAttribute

Attributes

AttributeUsageAttribute

Examples

The following code example demonstrates how you can apply the DataObjectFieldAttribute to a publicly exposed property to identify metadata associated with the property. In this example the NorthwindEmployee type exposes three data properties: EmployeeID, FirstName, and LastName. The DataObjectFieldAttribute attribute is applied to all three properties; however, only the EmployeeID property attribute indicates it is the primary key for the data row.

public class NorthwindEmployee
{
  public NorthwindEmployee() { }

  private int _employeeID;
  [DataObjectFieldAttribute(true, true, false)]
  public int EmployeeID
  {
    get { return _employeeID; }
    set { _employeeID = value; }
  }

  private string _firstName = String.Empty;
  [DataObjectFieldAttribute(false, false, true)]
  public string FirstName
  {
    get { return _firstName; }
    set { _firstName = value; }
  }

  private string _lastName = String.Empty;
  [DataObjectFieldAttribute(false, false, true)]
  public string LastName
  {
    get { return _lastName; }
    set { _lastName = value; }
  }
}

Public Class NorthwindEmployee

  Public Sub New()
  End Sub

  Private _employeeID As Integer
  <DataObjectFieldAttribute(True, True, False)> _
  Public Property EmployeeID() As Integer
    Get
      Return _employeeID
    End Get
    Set(ByVal value As Integer)
      _employeeID = value
    End Set
  End Property

  Private _firstName As String = String.Empty
  <DataObjectFieldAttribute(False, False, False)> _
  Public Property FirstName() As String
    Get
      Return _firstName
    End Get
    Set(ByVal value As String)
      _firstName = value
    End Set
  End Property

  Private _lastName As String = String.Empty
  <DataObjectFieldAttribute(False, False, False)> _
  Public Property LastName() As String
    Get
      Return _lastName
    End Get
    Set(ByVal value As String)
      _lastName = value
    End Set
  End Property

End Class

Remarks

Use the DataObjectFieldAttribute attribute to provide information about the schema of the underlying data. Design-time classes such as the ObjectDataSourceDesigner class use the DataObjectAttribute attribute to set properties at design-time based on the exposed schema.

You apply the DataObjectFieldAttribute attribute to members of the data item objects that are returned by the Select method of an object marked with the DataObjectAttribute attribute. In the following example, the NorthwindData class is marked with the DataObjectAttribute attribute, and returns an IEnumerable object containing NorthwindEmployee objects from the GetAllEmployees method. Fields in the NorthwindEmployee class are marked with the DataObjectFieldAttribute attribute to indicate they represent data fields in the underlying data source.

For more information about using attributes, see Attributes.

Constructors

DataObjectFieldAttribute(Boolean, Boolean, Boolean, Int32)	Initializes a new instance of the DataObjectFieldAttribute class and indicates whether the field is the primary key for the data row, whether it is a database identity field, and whether it can be null and sets the length of the field.
DataObjectFieldAttribute(Boolean, Boolean, Boolean)	Initializes a new instance of the DataObjectFieldAttribute class and indicates whether the field is the primary key for the data row, whether the field is a database identity field, and whether the field can be null.
DataObjectFieldAttribute(Boolean, Boolean)	Initializes a new instance of the DataObjectFieldAttribute class and indicates whether the field is the primary key for the data row, and whether the field is a database identity field.
DataObjectFieldAttribute(Boolean)	Initializes a new instance of the DataObjectFieldAttribute class and indicates whether the field is the primary key for the data row.

Properties

IsIdentity	Gets a value indicating whether a property represents an identity field in the underlying data.
IsNullable	Gets a value indicating whether a property represents a field that can be null in the underlying data store.
Length	Gets the length of the property in bytes.
PrimaryKey	Gets a value indicating whether a property is in the primary key in the underlying data.
TypeId	When implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute)

Methods

Equals(Object)	Returns a value indicating whether this instance is equal to a specified object.
GetHashCode()	Returns the hash code for this instance.
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)