RuleObjectExistsAttribute(String, DefaultContexts, String) Constructor

Initializes a new instance of the RuleObjectExistsAttribute class.

Namespace: DevExpress.Persistent.Validation

Assembly: DevExpress.Persistent.Base.v23.2.dll

NuGet Package: DevExpress.Persistent.Base

Declaration

C#

public RuleObjectExistsAttribute(
    string id,
    DefaultContexts targetContexts,
    string criteria
)

VB.NET

Public Sub New(
    id As String,
    targetContexts As DefaultContexts,
    criteria As String
)

Parameters

Name	Type	Description
id	String	A string value representing the current rule identifier. You can pass an empty value as the id parameter. An appropriate identifier will begenerated automatically, and set for the ID property of the Validation | Rules | Rule node in the Application Model.
targetContexts	DefaultContexts	A DefaultContexts enumeration value that specifies a context for checking the current rule. This value is set for the RuleBaseAttribute.TargetContextIDs property.
criteria	String	A string value representing the criteria that must be satisfied by the target type objects.

Remarks

If you are going to set a custom message template instead of a default one, use a constructor with the messageTemplate parameter.

The common rules of writing a criteria are described in the Ways to Build Criteria topic. In addition, you can use the following construction: PropertyName = '@PropertyName' (the operator is optional). @PropertyName represents a parameter that is set to the value of the PropertyName property of the currently validated object, when the rule is checked.

Related GitHub Examples

The following code snippet (auto-collected from DevExpress Examples) contains a reference to the RuleObjectExistsAttribute(String, DefaultContexts, String) constructor.

Note

The algorithm used to collect these code examples remains a work in progress. Accordingly, the links and snippets below may produce inaccurate results. If you encounter an issue with code examples below, please use the feedback form on this page to report the issue.

C#

xaf-how-to-implement-a-singleton-class/CS/HowToImplementSingleton.Module/Singleton.cs#L10

namespace HowToImplementSingleton.Module {
    [RuleObjectExists("AnotherSingletonExists", DefaultContexts.Save, "True", InvertResult = true,
    CustomMessageTemplate = "Another Singleton already exists.")]

VB.NET

xaf-how-to-implement-a-singleton-class/VB/HowToImplementSingleton.Module/Singleton.vb#L10

Namespace HowToImplementSingleton.Module
    <RuleObjectExists("AnotherSingletonExists", DefaultContexts.Save, "True", InvertResult := True, CustomMessageTemplate := "Another Singleton already exists."), RuleCriteria("CannotDeleteSingleton", DefaultContexts.Delete, "False", CustomMessageTemplate := "Cannot delete Singleton.")> _
    Public Class Singleton