DotThrow 2.0.2

DotThrow

Guard clauses and validation for .NET, with one set of checks. As a guard clause, a chain of checks throws the right exception with the parameter name filled in. In collect mode, the same checks record every error in a report that you can return from an API. Validator<T> has the features of FluentValidation 12.

• More than 110 checks: strings, numbers, dates, collections, dictionaries, enums, URIs, IP addresses, streams and types.
• MIT licensed, no dependencies.
• Checks on numbers, strings, dates, enums and in-memory collections allocate nothing when they pass.
• Message templates with placeholders, and translations for 58 cultures in 54 languages.
• Rules from JSON or IConfiguration (DotThrow.Dynamic), updated at run time.
• Roslyn analyzers and code fixes in the package, for example for a chain without checks.
• Targets netstandard2.0, netstandard2.1, net462, net8.0, net9.0 and net10.0. Trimming and Native AOT safe on .NET 8 and later.

Install

dotnet add package DotThrow

Packages

The DotThrow packages share one version:

• DotThrow (this package): guard clauses, collect mode, Validator<T>, dynamic rules, message translations and analyzers. No dependencies.
• DotThrow.DependencyInjection: register validators in dependency injection, validate options classes, and dynamic validators from configuration.
• DotThrow.AspNetCore: validation for minimal API endpoints and MVC actions, and validation problem helpers.

Guard clauses

using DotThrow;

public sealed class Customer
{
    public Customer(string name, string email, int age)
    {
        Name = name.Throw().IfNullOrWhiteSpace().IfLongerThan(100);
        Email = email.Throw().IfNullOrWhiteSpace().IfNotEmailAddress();
        Age = age.Throw().IfOutOfRange(0, 150);
    }

    public string Name { get; }

    public string Email { get; }

    public int Age { get; }
}

new Customer("Ada Lovelace", "ada@example.com", 200) throws:

System.ArgumentOutOfRangeException: 'age' must be between 0 and 150. (Parameter 'age')
Actual value was 200.

Collect every error

var form = new SignUpForm(Name: "", Email: "ada.example.com", Age: 12);

var report = new ValidationReport();
report.Check(form, f => f.Name).IfNullOrWhiteSpace();
report.Check(form, f => f.Email).IfNullOrWhiteSpace().IfNotEmailAddress();
report.Check(form, f => f.Age).IfLessThan(13, "You must be 13 or older.");

Console.WriteLine(report);

public sealed record SignUpForm(string Name, string Email, int Age);

Validation failed with 3 errors:
 - Name: 'Name' must not be empty or white space.
 - Email: 'Email' must be a valid email address.
 - Age: You must be 13 or older.

In ASP.NET Core, Results.ValidationProblem(report.ToDictionary()) turns the report into a standard 400 response.

Reusable validators

public sealed class SignUpFormValidator : Validator<SignUpForm>
{
    public SignUpFormValidator()
    {
        For(x => x.Name, name => name.IfNullOrWhiteSpace().IfLongerThan(100));
        For(x => x.Email, email => email.IfNullOrWhiteSpace().IfNotEmailAddress(), rule => rule
            .WithMessage("Please check the email address."));
        For(x => x.Age, age => age.IfLessThan(13, "You must be 13 or older."));
    }
}

var validator = new SignUpFormValidator();
ValidationReport result = validator.Validate(new SignUpForm("Ada Lovelace", "ada@example.com", 36));

Validators also handle nested objects, collections, conditions, groups, severity, async rules and polymorphic types, and DotThrow.Testing has test helpers with the names of FluentValidation's TestHelper.

Learn more

• Documentation and source
• Every check
• Validation
• DotThrow for FluentValidation users
• Messages and localization
• Dynamic rules
• Dependency injection and ASP.NET Core
• Analyzers
• Writing your own checks
• Performance
• Migrating from DotThrow 1.x
• Release notes