Immediate.Validations

Immediate.Validations is a source generator validating Immediate.Handlers handler parameters.

Installing Immediate.Validations

You can install Immediate.Validations with NuGet:

Install-Package Immediate.Validations

Or via the .NET Core command line interface:

dotnet add package Immediate.Validations

Either command, from Package Manager Console or .NET Core CLI, will download and install Immediate.Validations.

Using Immediate.Validations

Add Immediate.Validations to the Immediate.Handlers behaviors pipeline by including it in the list of default Behaviors for the assembly:

using Immediate.Validations.Shared;

[assembly: Behaviors(
	typeof(ValidationBehavior<,>)
)]

Creating Validation Classes

Indicate that a class should be validated by adding the [Validate] attribute and IValidationTarget<> interface:

[Validate]
public partial record Query : IValidationTarget<Query>;

When Nullable Reference Types is enabled, any non-nullable reference types are automatically checked for null. Other validations are available like so:

[Validate]
public partial record Query : IValidationTarget<Query>
{
	[GreaterThan(0)]
	public required int Id { get; init; }
}

Referencing Other Properties

Since attributes cannot reference anything other than constant strings, the way to reference static and instance properties, fields, and methods is to use the nameof() to identify which property, field, or method should be used. Example:

[Validate]
public partial record Query : IValidationTarget<Query>
{
	[GeneratedRegex(@"^\d+$")]
	private static partial Regex AllDigitsRegex();

	[Match(regex: nameof(AllDigitsRegex))]
	public required string Id { get; init; }
}

Custom Messages

Provide a custom message to any validation using the Message property of the attribute. This message will be parsed for template parameters, which will be applied to the message before rendering to the validation result. The target property name is available as {PropertyName}, and it's value via {PropertyValue}.

Other parameter values will be added using their property name suffixed with Value (for example, the GreaterThanAttribute uses a comparison parameter, so the value is available via ComparisonValue). If another property on the target class is referenced via nameof(Property), the name of that property will be available using the Name suffix (for example, ComparisonName for the comparison property).

[Validate]
public partial record Query : IValidationTarget<Query>
{
	[GreaterThan(0, Message = "'{PropertyName}' must be greater than '{ComparisonValue}'")]
	public required int Id { get; init; }
}

Extending Validation Classes

If attributes are not enough to specify how to validate a class, an AdditionalValidations method can be used to write additional validations for the class.

[Validate]
public partial record Query : IValidationTarget<Query>
{
	public required bool Enabled { get; init; }
	public required int Id { get; init; }

	private static void AdditionalValidations(
		ValidationResult errors,
		Query target
	)
	{
		if (target.Enabled)
		{
			// Use a lambda to use the default message or override message;
			// the message will be templated in the same way as attribute validations.
			errors.Add(
				() => GreaterThanAttribute.ValidateProperty(
					target.Id,
					0
				)
			);
		}

		if (false)
		{
			// Manually create a `ValidationError` and add it to the `ValidationResult`.
			errors.Add(
				new ValidationError()
				{
					PropertyName = "ExampleProperty",
					ErrorMessage = "Example Message",
				}
			)
		}
	}
}

Results

The result of doing the above is that when a parameter fails one or more validations, a ValidationException is thrown, which can be handled via ProblemDetails or any other infrastructure mechanism.

Example using ProblemDetails:

builder.Services.AddProblemDetails(ConfigureProblemDetails);

public static void ConfigureProblemDetails(ProblemDetailsOptions options) =>
	options.CustomizeProblemDetails = c =>
	{
		if (c.Exception is null)
			return;

		c.ProblemDetails = c.Exception switch
		{
			ValidationException ex => new ValidationProblemDetails(
				ex
					.Errors
					.GroupBy(x => x.PropertyName, StringComparer.OrdinalIgnoreCase)
					.ToDictionary(
						x => x.Key,
						x => x.Select(x => x.ErrorMessage).ToArray(),
						StringComparer.OrdinalIgnoreCase
					)
			)
			{
				Status = StatusCodes.Status400BadRequest,
			},

			// other exception handling as desired

			var ex => new ProblemDetails
			{
				Detail = "An error has occurred.",
				Status = StatusCodes.Status500InternalServerError,
			},
		};

		c.HttpContext.Response.StatusCode =
			c.ProblemDetails.Status
			?? StatusCodes.Status500InternalServerError;
	};