ValidatR

Simple attribute based validations where validation rule values are fetched through Func to let the consumer decide the values based on field, validationtype and a parameter which can be sent in the ValidateAsync or fetched through a parameter resolver.

Use cases

• Validation rules needs to be different based on model property value (using parameter resolver)
  • Example: All validation rules needs to be different based on a property value
  • Example: Validation rules differ for CreateCustomerRequest depending on country
• Validation rules needs to be different based on external value (the parameter is provided in the validate method)
  • Example: Vary rules based on countryCode sent in route to controller

ValidateAttribute

To add validation rules to a model use the [Validate("id", ValidatorType | ValidatorType)] attribute. Example:

public class CreateCustomerRequest 
{
    [Validate("CreateCustomerRequest.FirstName", ValidatorType.Regex | ValidatorType.Required)]
    public string FirstName { get; set; }

    [Validate("CreateCustomerRequest.Address", ValidatorType.Required)]
    public Address Address { get; set; }
    ...
}

public class Address
{
    [Validate("Address.Street", ValidatorType.Required | ValidatorType.MaxLength)]
    public string Street { get; set; }
}

Validate attribute can also be used on complex types, but in that case only required is supported on the nested type in the class used to trigger validation. OBS! Validation will only be performed on properties using the Validate attribute, and no exception will be thrown if no Validate attribute exists in a class used in the ValidateAsync method

Example registration

builder.Services.AddValidatR<string>().AddParameterResolver<CreateCustomerRequest>(x => x.LastName);

In the above example, we also add a parameter resolver to be able to resolve a model without specifying the parameter value to send to the func when retrieving the validation rule value.

If there i a need to use a service in the func (as in the example application), use the IApplicationBuilder extension below (The func in the AddValidatR is optional).

app.UseValidatR<string>()
    .AddMinLengthValidator(id, parameter) =>
{
    var storageService = app.Services.GetRequiredService<IStorageService>();
    return storageService.GetValidationRuleValue(id, ValidatorType.MinLength, parameter);
});

Validation

There are 3 ways to validate

• Injecting IValidator<TParameter>, where TParameter is the type of the key used in the func
• Injecting IValidator, requires adding Parameter resolvers for the types being validated otherwise an exception will be thrown.
• Using the middleware.

Using the middleware

The middleware validates the request model and returns badrequest with a HttpValidationProblemDetails response if errors are found. When using the AddValidatorMiddleware applicationBuilder extension the extension method scans all loaded assemblies for classes with properties using the ValidateAttribute to automatically register a middleware for each of the classes. To explicitly tell ValidatR which classes to use, the extension methods supports params Type[] to specify the types to load middlewares for.