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MiniValidationPlus

👉 with support of non-nullable reference types.

A minimalistic validation library built atop the existing features in .NET's System.ComponentModel.DataAnnotations namespace. Adds support for single-line validation calls and recursion with cycle detection.

This project is fork of the original great repo MiniValidation from Damian Edwards and adds support of non-nullable reference types. Now validation works more like validation in model binding of ASP.NET Core MVC.

Supports .NET Standard 2.0 compliant runtimes.

Installation

Nuget

Install the library from NuGet:

❯ dotnet add package MiniValidationPlus

ASP.NET Core 6+ Projects

If installing into an ASP.NET Core 6+ project, consider using the MinimalApis.Extensions package instead, which adds extensions specific to ASP.NET Core, including a validation endpoint filter for .NET 7 apps:

❯ dotnet add package MinimalApis.Extensions

Example usage

Validate an object

var widget = new Widget { Name = "" };

var isValid = MiniValidatorPlus.TryValidate(widget, out var errors);

class Widget
{
    [Required, MinLength(3)]
    public string Name { get; set; }
    
    // Non-nullable reference types are required automatically
    public string Category { get; set; }

    public override string ToString() => Name;
}

Skip validation

You can set property to be skipped when validation is performed by setting SkipValidationAttribute on it. If you want to perform validation on the property, but not to validate it recursively (validate properties of the property), you can set SkipRecursionAttribute on it.

When you use SkipValidationAttribute on a property, recursion is also skipped for that property.

class Model
{
    [SkipValidation]
    public string Name => throw new InvalidOperationException();

    public ValidChild ValidChild { get; set; }

    public ValidChildWithInvalidSkippedProperty ValidChildWithInvalidSkippedProperty { get; set; }

    [SkipRecursion]
    public InvalidChild InvalidChild { get; set; }
}

class ValidChild
{
    [Range(10, 100)]
    public int TenOrMore { get; set; } = 10;
}

class ValidChildWithInvalidSkippedProperty
{
    // Property is invalid but is skipped
    [SkipValidation]
    public string Name { get; set; } = null!;
}

class InvalidChild
{
    // Property is invalid
    [Range(10, 100)]
    public int TenOrMore { get; set; } = 3;
}

Opt-out validation of non-nullable reference types

You can disable validation of properties that are non-nullable reference types by configuring ValidationSettings:

var validationSettings = ValidationSettings.Default with { ValidateNonNullableReferenceTypes = false };
var isValid = MiniValidatorPlus.TryValidate(objectToValidate, validationSettings, out var errors);

Use services from validators

var widget = new Widget { Name = "" };

// Get your serviceProvider from wherever makes sense
var serviceProvider = ...
var isValid = MiniValidatorPlus.TryValidate(widget, serviceProvider, out var errors);

class Widget : IValidatableObject
{
    [Required, MinLength(3)]
    public string Name { get; set; }
    
    // Non-nullable reference types are required automatically
    public string Category { get; set; }

    public override string ToString() => Name;

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        var disallowedNamesService = validationContext.GetService(typeof(IDisallowedNamesService)) as IDisallowedNamesService;

        if (disallowedNamesService is null)
        {
            throw new InvalidOperationException($"Validation of {nameof(Widget)} requires an {nameof(IDisallowedNamesService)} instance.");
        }

        if (disallowedNamesService.IsDisallowedName(Name))
        {
            yield return new($"Cannot name a widget '{Name}'.", new[] { nameof(Name) });
        }
    }
}

Console app

using System.ComponentModel.DataAnnotations;
using MiniValidationPlus;

var nameAndCategory = args.Length > 0 ? args[0] : "";

var widgets = new List<Widget>
{
    new Widget { Name = nameAndCategory, Category = nameAndCategory },
    new WidgetWithCustomValidation { Name = nameAndCategory, Category = nameAndCategory }
};

foreach (var widget in widgets)
{
    if (!MiniValidatorPlus.TryValidate(widget, out var errors))
    {
        Console.WriteLine($"{nameof(Widget)} has errors!");
        foreach (var entry in errors)
        {
            Console.WriteLine($"  {entry.Key}:");
            foreach (var error in entry.Value)
            {
                Console.WriteLine($"  - {error}");
            }
        }
    }
    else
    {
        Console.WriteLine($"{nameof(Widget)} '{widget}' is valid!");
    }
}

class Widget
{
    [Required, MinLength(3)]
    public string Name { get; set; }
    
    // Non-nullable reference types are required automatically
    public string Category { get; set; }

    public override string ToString() => Name;
}

class WidgetWithCustomValidation : Widget, IValidatableObject
{
    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if (string.Equals(Name, "Widget", StringComparison.OrdinalIgnoreCase))
        {
            yield return new($"Cannot name a widget '{Name}'.", new[] { nameof(Name) });
        }
    }
}
❯ widget.exe
Widget has errors!
  Name:
  - The Widget name field is required.
  Category:
  - The Category field is required.
Widget has errors!
  Name:
  - The Widget name field is required.
  Category:
  - The Category field is required.

❯ widget.exe Ok
Widget has errors!
  Name:
  - The field Widget name must be a string or array type with a minimum length of '3'.
Widget has errors!
  Name:
  - The field Widget name must be a string or array type with a minimum length of '3'.

❯ widget.exe Widget
Widget 'Widget' is valid!
Widget has errors!
  Name:
  - Cannot name a widget 'Widget'.

❯ widget.exe MiniValidationPlus
Widget 'MiniValidationPlus' is valid!
Widget 'MiniValidationPlus' is valid!

Web app (.NET 6)

using System.ComponentModel.DataAnnotations;
using MiniValidationPlus;

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", () => "Hello World");

app.MapGet("/widgets", () =>
    new[] {
        new Widget { Name = "Shinerizer" },
        new Widget { Name = "Sparklizer" }
    });

app.MapGet("/widgets/{name}", (string name) =>
    new Widget { Name = name });

app.MapPost("/widgets", (Widget widget) =>
    !MiniValidatorPlus.TryValidate(widget, out var errors)
        ? Results.ValidationProblem(errors)
        : Results.Created($"/widgets/{widget.Name}", widget));

app.MapPost("/widgets/custom-validation", (WidgetWithCustomValidation widget) =>
    !MiniValidatorPlus.TryValidate(widget, out var errors)
        ? Results.ValidationProblem(errors)
        : Results.Created($"/widgets/{widget.Name}", widget));

app.Run();

class Widget
{
    [Required, MinLength(3)]
    public string? Name { get; set; }

    public override string? ToString() => Name;
}

class WidgetWithCustomValidation : Widget, IValidatableObject
{
    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if (string.Equals(Name, "Widget", StringComparison.OrdinalIgnoreCase))
        {
            yield return new($"Cannot name a widget '{Name}'.", new[] { nameof(Name) });
        }
    }
}