ilya.rudenka/FlatValidatorv2.1.0

The FlatValidator is a validation library for .NET that delivers an high performance and memory prudence by using lambda-based and strongly-typed rules.

Quick examples

In general, there are two simple ways to validate custom data with the FlatValidator.

1. Inline mode

You can define validation rules in your code to validate object locally.

var model = new Model(Email: "email", BirthDate: DateTime.Now, Rate: -100);

// synchronous version
var result =  FlatValidator.Validate(model, v =>
{
    // IsEmail() is one of funcs for typical data formats like Phone, Url, CreditCard, etc.
    v.ValidIf(m => m.Email.IsEmail(), "Invalid email", m => m.Email);

    v.ErrorIf(m => m.Rate < 0, "Negative Rate", m => m.Rate);

    v.WarningIf(m => m.BirthDate.AddYears(10) >= DateTime.Now, 
                "Age looks like incorrect", m => m.BirthDate);
});
if (!result) 
{
    // ToDictionary() => Dictionary<PropertyName, ErrorMessage[]>
    return TypedResults.ValidationProblem(result.ToDictionary()) 
}

// or asynchronous version
var result = await FlatValidator.ValidateAsync(model, v => 
{
    v.ErrorIf(async m => await userService.IsUserExistAsync(m.Email),
              "User already registered", m => m.Email);

    // the same without `async/await`
    v.ErrorIf(m => userService.IsUserExistAsync(m.Email),
              m => $"Email {m.Email} already registered", 
              m => m.Email);
});

2. Inheritance of the FlatValidator class

Another way is to inherit the FlatValidator to define custom rules in the constructor. Also you can pass dependencies into constructor to get additional functionality inside of the validation rules.

public record UserModel(string Forename, string Surname, ....);

public class UserValidator: FlatValidator<UserModel> 
{
    public UserValidator(ILogger logger, IPostalService postalService) 
    {
        logger.LogInfo("Validating...");

        ErrorIf(m => m.Forename.IsEmpty(), "Forename can not be empty.", m => m.Forename);
        ErrorIf(m => m.Surname.IsEmpty(), "Surname can not be empty.", m => m.Surname);
        
        // you can define one or more groups of preconditions
        If(m => m.ShipmentAddress.NotEmpty(), @then: m =>
        {
            ValidIf(async m => await postalService.AddressExistsAsync(m.Address),
                     "Postal address not found.", m => m.Address);

            WarningIf(m => !m.Phone.IsPhone(), "No contact phone.");
        },
        @else: m => // optionally
        {
            ValidIf(m => m.Phone.IsPhone(), "invalid phone number.", m => m.Phone);
        });
    }
}