Vergosity Rule Engine + Fluent API

The Vergosity Rule Engine is now easier to use with Fluent API features. Basically, there is a ValidationContext object that  you can add and configure rules using fluent API style syntax. If you are not familiar with the ValidationContext – it is contained in the Vergosity.Validation namespace. And if you are not familiar with Vergosity, you can get from Nuget: Install-package Vergosity.Framework. Or search by “Vergosity” in your “Manage Nuget Packages” reference option.



The Vergosity Rule Engine contains a set of rules already implemented. You can start by adding them to an instance of the ValidationContext. There are (2) ways to use the new Fluent API. You just need to create an instance of the ValidationContext.

ValidationContextBase context = new ValidationContext();


Option 1, shown below is the easiest way to add a new rule to the ValidationContext. All of the new Fluent API calls are prefixed using “With”. This provides a nice filter for your methods. Below, an entity is setup for the unit test and is used as the target parameter in the IsNotNull rule.


When you call the RenderRules() method of the ValidationContext – you can retrieve the results from the Results list. You can use the results any way you prefer in your application. The ValidationContext also contains results filtered by the Severity indicated in the rule configuration.

  • ValidationContext.ExceptionResults;
  • ValidationContext.InformationResults;
  • ValidationContext.WarningResults;


With Configuration

The unit test below shows another option that includes rule configuration – this is where the fluent api really helps out. After you add the rule to the ValidationContext, you are ready to start configuring the specified rule using a set of methods that are prefixed by “With”.


Custom Business Rules

There will be situations where you need to create a custom business rules. The Vergosity Framework contains the framework classes for you to create simple or complex rules. We will show you how to create these rules – and then use them in your code.

Simple Rule

Simple rules inherit from the Vergosity Framework class called Rule. You modify the constructor to send in your target. The Render() method is where you implement the rule’s validation logic. You will need set the IsValid property to true/false based on the rule logic – then, you will return a new Result object as show below.

Simple rules allow you create rules that can be used or composed into composite rules. The rule rendering using the ValidationContext is consistent whether the rule is a simple or composite rule. Therefore, you have a lot of flexibility in managing business rules for you business logic.


Composite Rule

You can create a custom rule that contains any of the default rules and/or other custom rules. This allows you to compose your custom rule to contain whatever rule-set you require for you business logic. The composite rule will inherit from the Vergosity Framework class called: RuleComposite. Creating a custom rule allows you to reuse the rule from one or more locations in your code. You are also encapsulating the rule implementation into a single rule – therefore, you will only have one place to modify or extend you rule implementation.

Building the rule set is similar to the previous example in the unit tests. However, in the actual rule, you use the Rules list to add rules.


The following is the code snippet from the composite rule class. If you have noticed the WithPriority setting, this allows you to set or arrange the order that the rules are evaluated.

    .WithMessage(“The name value is not valid.”)

this.Rules.WithAreNotEqual(entity.DateOfBirth, new DateTime())
    .WithMessage(“Date contains the default DateTime value.”)

this.Rules.WithRange(entity.FavoriteNumber, 1, 100)
    .WithMessage(string.Format(“The favorite number value is not within the specified range: {0}-{1}”, 1, 100))

    .WithMessage(“The entity id is not valid. Cannot be empty Guid value.”);