Not Null Validator

Microsoft Enterprise Library 5.0

previous page next page
DropDown image DropDownHover image Collapse image Expand image CollapseAll image ExpandAll image Copy image CopyHover image

Class Name: NotNullValidator

Attribute Name: NotNullValidatorAttribute

Configuration tool name: Not Null Validator

Description

This validator checks that the value is not null (C#) or Nothing (Visual Basic).

Properties

The following table lists the Not Null validator properties. The actual property names shown in the configuration tools are listed in the table description.

Property

Description

MessageTemplate

Message Template - This property is a string containing template tokens that the validator replaces with values as it validates the target. Typically, it describes the validation result.

MessageTemplateResourceName

Template Resource Name - If you do not want to use the MessageTemplate property to hard-code a message template (perhaps for internationalization), you can use a template stored in the application resources. You must also specify a MessageTemplateResourceType value. If you include both a MessageTemplate value and a MessageTemeplateResourceName value, the MessageTemplate value takes precedence.

MessageTemplateResourceType

Template Resource Type - The resource type for the template you want to use. If you specify a MessageTemplateResourceName value, you must specify this value.

Name

Name – The name to use for this validator.

Negated

Negated - This is a Boolean property. If it is set to True, it changes the validator's behavior so that it will fail if the condition is met instead of when it is not met. The default is False.

Tag

Tag - This property is a user-supplied string. Typically, it is used to sort or categorize validation results.

TypeName

Type Name – The fully qualified name of the type configuration element. This property cannot be edited.

Message Template Tokens

If the message template contains tokens (for example, "{0}"), the validator will replace these tokens with values when the ValidationResult is created. The tokens supported by the Not Null validator are listed in the following table.

Token

Meaning

{0}

This token represents the value of the object that is being validated. Although it can be useful to show the original value as a part of the validation message, you must be careful to avoid injection attacks by escaping any characters that can be used to attack the system that conveys the message to the user.

{1}

This token represents the key of the object that is being validated. When the validator is attached to a member of a type such as a property or a field, the key is set to the member name. When the validator is attached to an object, the key is null and the token is replaced by an empty string.

{2}

This token represents the tag that is specified on the validator instance. If no tag is supplied, the token is replaced by an empty string.

Example

The following code example shows how to use the validator with attributes to ensure that a value is not null.

C# Copy Code 
public class Product
{
  [NotNullValidator]
  public Company Manufacturer
  {
    get
    {
      return manufacturer;
    }
  }
  // ...
}
Visual Basic Copy Code 
Public Class Product
  <NotNullValidator()> _
  ReadOnly Property Manufacturer(ByVal _manufacturer As Company)
    Get
      Return _manufacturer
    End Get
  End Property
  ' ...
End Class

previous page start next page