Create business rules in a simple and elegant way.

1. Generate a new GitHub Personal Access Token with read:packages permission.

2. Add a new NuGet source:

   # Substitute <USERNAME> with your GitHub username and <TOKEN> with your Personal Access Token.
   
   dotnet nuget add source 'https://nuget.pkg.github.com/akeeller/index.json' --name 'github-akeeller' --username <USERNAME> --password <TOKEN>

   On platforms other than Windows, you might need to add the option --store-password-in-clear-text.

3. While in the root folder of your project, simply add the package AKeeller.Rule:

   dotnet add package AKeeller.Rule

🧑‍💻 In the following examples the using AKeeller.Rule directive has been omitted for simplicity.

First of all, create a meaningful subclass of Rule<>.
IsEven can be a good choice to start practicing:

public class IsEven : Rule<int>
{
  protected override ValidationResult PartialValidation(int data) =>
    new() { IsValid = data % 2 is 0 };
}

You only need to implement a single method which returns a ValidationResult. The latter is a struct with only two properties:

• bool IsValid
• List<string> Messages

That's it. Now we're ready to use our business rule to validate an int.

In your main, create an instance of IsEven and use it to validate your data. Then, use the ValidationResult to do your stuffs.

int number = 10;
var rule = new IsEven();
var result = rule.Validate(number);

Console.WriteLine(result.IsValid ? "Valid!" : "Not valid"); // Outputs: Valid!

Now the most important part. You can chain as many rules as you want to validate your data. Let's say we created three Rules: IsEven, IsPerfectSquare and IsPalindromic. We could check all these rules in one simple step like this:

var number = 676;

var rule = new IsEven()
  .AddRule(new IsPerfectSquare())
  .AddRule(new IsPalindromic());

var result = rule.Validate(number);

Console.WriteLine(result.IsValid ? "Valid!" : "Not valid"); // Outputs: Valid!

It's also possible to include one ore more messages in your validation results. Let's see how they work.

In one of yours Rules, add a Message to the ValidationResult:

public class IsEven : Rule<int>
{
  protected override ValidationResult PartialValidation(int data)
  {
    var result = new ValidationResult
    {
      IsValid = data % 2 == 0
    };

    if (result.IsNotValid)
      result.Messages.Add("This number is not even!");

    return result;
  }
}

As you can see, a Message is added if the number is not even.

In your main, you can read messages like this:

var number = 7;
var rule = new IsEven();
var result = rule.Validate(number);

foreach (string message in result.Messages)
  Console.WriteLine(message); // Outputs: This number is not even!

The idea is to receive error, status and info messages from every rule.