MicroElements.Swashbuckle.FluentValidation

Use FluentValidation rules instead of ComponentModel attributes to define swagger schema.

Note: For WebApi see: https://github.com/micro-elements/MicroElements.Swashbuckle.FluentValidation.WebApi

Statuses

Supporting the project

MicroElements.Swashbuckle.FluentValidation is developed and supported by @petriashev for free in his spare time. If you find MicroElements.Swashbuckle.FluentValidation useful, please consider financially supporting the project via OpenCollective which will help keep the project going 🙏.

Usage

1. Minimal API

MinimalApi.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">

    <PropertyGroup>
        <TargetFramework>net7.0</TargetFramework>
        <Nullable>enable</Nullable>
        <ImplicitUsings>enable</ImplicitUsings>
    </PropertyGroup>

    <ItemGroup>
        <PackageReference Include="FluentValidation.AspNetCore" Version="11.2.2" />
        <PackageReference Include="MicroElements.Swashbuckle.FluentValidation" Version="6.0.0" />
        <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="7.0.2" />
        <PackageReference Include="Swashbuckle.AspNetCore" Version="6.4.0" />
    </ItemGroup>
    
</Project>

Program.cs

using FluentValidation;
using FluentValidation.AspNetCore;
using MicroElements.Swashbuckle.FluentValidation.AspNetCore;

var builder = WebApplication.CreateBuilder(args);
var services = builder.Services;

// Asp.Net stuff
services.AddControllers();
services.AddEndpointsApiExplorer();

// Add Swagger
services.AddSwaggerGen();

// Add FV
services.AddFluentValidationAutoValidation();
services.AddFluentValidationClientsideAdapters();

// Add FV validators
services.AddValidatorsFromAssemblyContaining<Program>();

// Add FV Rules to swagger
services.AddFluentValidationRulesToSwagger();

var app = builder.Build();

// Use Swagger
app.UseSwagger();
app.UseSwaggerUI();

app.MapControllers();

app.Run();

2. AspNetCore WebApi

Reference packages in your web project

<PackageReference Include="FluentValidation.AspNetCore" Version="11.1.0" />
<PackageReference Include="MicroElements.Swashbuckle.FluentValidation" Version="6.0.0" />
<PackageReference Include="Swashbuckle.AspNetCore" Version="6.3.0" />

Change Startup.cs

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
    // Asp.net stuff
    services.AddControllers();
    
    // HttpContextValidatorRegistry requires access to HttpContext
    services.AddHttpContextAccessor();

    // Register FV validators
    services.AddValidatorsFromAssemblyContaining<Startup>(lifetime: ServiceLifetime.Scoped);

    // Add FV to Asp.net
    services.AddFluentValidationAutoValidation();

    // Add swagger
    services.AddSwaggerGen(c =>
    {
        c.SwaggerDoc("v1", new OpenApiInfo { Title = "My API", Version = "v1" });
    });

    // [Optional] Add INameResolver (SystemTextJsonNameResolver will be registered by default)
    // services.AddSingleton<INameResolver, CustomNameResolver>();

    // Adds FluentValidationRules staff to Swagger. (Minimal configuration)
    services.AddFluentValidationRulesToSwagger();

    // [Optional] Configure generation options for your needs. Also can be done with services.Configure<SchemaGenerationOptions>
    // services.AddFluentValidationRulesToSwagger(options =>
    // {
    //     options.SetNotNullableIfMinLengthGreaterThenZero = true;
    //     options.UseAllOffForMultipleRules = true;
    // });

    // Adds logging
    services.AddLogging(builder => builder.AddConsole());
}

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseRouting();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
    });

    // Adds swagger
    app.UseSwagger();

    // Adds swagger UI
    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");
    });
}

Version compatibility

Sample application

See sample project: https://github.com/micro-elements/MicroElements.Swashbuckle.FluentValidation/tree/master/samples/SampleWebApi

Supported validators

• INotNullValidator (NotNull)
• INotEmptyValidator (NotEmpty)
• ILengthValidator (for strings: Length, MinimumLength, MaximumLength, ExactLength) (for arrays: MinItems, MaxItems)
• IRegularExpressionValidator (Email, Matches)
• IComparisonValidator (GreaterThan, GreaterThanOrEqual, LessThan, LessThanOrEqual)
• IBetweenValidator (InclusiveBetween, ExclusiveBetween)

Extensibility

You can register FluentValidationRule in ServiceCollection.

User defined rule name replaces default rule with the same. Full list of default rules can be get by FluentValidationRules.CreateDefaultRules()

List or default rules:

• Required
• NotEmpty
• Length
• Pattern
• Comparison
• Between

Example of rule:

new FluentValidationRule("Pattern")
{
    Matches = propertyValidator => propertyValidator is IRegularExpressionValidator,
    Apply = context =>
    {
        var regularExpressionValidator = (IRegularExpressionValidator)context.PropertyValidator;
        context.Schema.Properties[context.PropertyKey].Pattern = regularExpressionValidator.Expression;
    }
},

Samples

Swagger Sample model and validator

public class Sample
{
    public string PropertyWithNoRules { get; set; }

    public string NotNull { get; set; }
    public string NotEmpty { get; set; }
    public string EmailAddress { get; set; }
    public string RegexField { get; set; }

    public int ValueInRange { get; set; }
    public int ValueInRangeExclusive { get; set; }

    public float ValueInRangeFloat { get; set; }
    public double ValueInRangeDouble { get; set; }
}

public class SampleValidator : AbstractValidator<Sample>
{
    public SampleValidator()
    {
        RuleFor(sample => sample.NotNull).NotNull();
        RuleFor(sample => sample.NotEmpty).NotEmpty();
        RuleFor(sample => sample.EmailAddress).EmailAddress();
        RuleFor(sample => sample.RegexField).Matches(@"(\d{4})-(\d{2})-(\d{2})");

        RuleFor(sample => sample.ValueInRange).GreaterThanOrEqualTo(5).LessThanOrEqualTo(10);
        RuleFor(sample => sample.ValueInRangeExclusive).GreaterThan(5).LessThan(10);

        // WARNING: Swashbuckle implements minimum and maximim as int so you will loss fraction part of float and double numbers
        RuleFor(sample => sample.ValueInRangeFloat).InclusiveBetween(1.1f, 5.3f);
        RuleFor(sample => sample.ValueInRangeDouble).ExclusiveBetween(2.2, 7.5f);
    }
}

Swagger Sample model screenshot

Validator with Include

public class CustomerValidator : AbstractValidator<Customer>
{
    public CustomerValidator()
    {
        RuleFor(customer => customer.Surname).NotEmpty();
        RuleFor(customer => customer.Forename).NotEmpty().WithMessage("Please specify a first name");

        Include(new CustomerAddressValidator());
    }
}

internal class CustomerAddressValidator : AbstractValidator<Customer>
{
    public CustomerAddressValidator()
    {
        RuleFor(customer => customer.Address).Length(20, 250);
    }
}

Get params bounded to validatable models

MicroElements.Swashbuckle.FluentValidation updates swagger schema for operation parameters bounded to validatable models.

Defining rules dynamically from database

See BlogValidator in sample.

Common problems and workarounds

Error: System.InvalidOperationException: 'Cannot resolve 'IValidator<T>' from root provider because it requires scoped service 'TDependency'

Workarounds in order or preference:

Workaround 1 (Use HttpContextServiceProviderValidatorFactory) by @WarpSpideR

public void ConfigureServices(IServiceCollection services)
{
    // HttpContextServiceProviderValidatorFactory requires access to HttpContext
    services.AddHttpContextAccessor();

    services
        .AddMvc()
        // Adds fluent validators to Asp.net
        .AddFluentValidation(c =>
        {
            c.RegisterValidatorsFromAssemblyContaining<Startup>();
            // Optionally set validator factory if you have problems with scope resolve inside validators.
            c.ValidatorFactoryType = typeof(HttpContextServiceProviderValidatorFactory);
        });

Workaround 2 (Use ScopedSwaggerMiddleware)

Replace UseSwagger for UseScopedSwagger:

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app
        .UseMvc()
        // Use scoped swagger if you have problems with scoped services in validators
        .UseScopedSwagger();

Workaround 3 (Set ValidateScopes to false)

public static IWebHost BuildWebHost(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        // Needed for using scoped services (for example DbContext) in validators
        .UseDefaultServiceProvider(options => options.ValidateScopes = false)
        .UseStartup<Startup>()
        .Build();

Problem: I cant use several validators of one type

Example: You split validator into several small validators but AspNetCore uses only one of them.

Workaround: Hide dependent validators with internal and use Include to include other validation rules to one "Main" validator.

Problem: I'm using FluentValidation or FluentValidation.DependencyInjectionExtensions instead of FluentValidation.AspNetCore

If you are using the more basic FluentValidation or FluentValidation.DependencyInjectionExtensions libraries, then they will not automatically register IValidatorFactory and you will get an error at runtime: "ValidatorFactory is not provided. Please register FluentValidation." In that case you must register it manually (see issue 97 for more details):

services.TryAddTransient<IValidatorFactory, ServiceProviderValidatorFactory>();
services.AddFluentValidationRulesToSwagger();

Problem: Newtonsoft.Json DefaultNamingStrategy, SnakeCaseNamingStrategy does not work

Startup.cs:

    .AddJsonOptions(options =>
    {
        options.JsonSerializerOptions.PropertyNamingPolicy = new NewtonsoftJsonNamingPolicy(new SnakeCaseNamingStrategy());
        //options.JsonSerializerOptions.DictionaryKeyPolicy = new NewtonsoftJsonNamingPolicy(new SnakeCaseNamingStrategy());
    })


    /// <summary>
    /// Allows use Newtonsoft <see cref="NamingStrategy"/> as System.Text <see cref="JsonNamingPolicy"/>.
    /// </summary>
    public class NewtonsoftJsonNamingPolicy : JsonNamingPolicy
    {
        private readonly NamingStrategy _namingStrategy;

        /// <summary>
        /// Creates new instance of <see cref="NewtonsoftJsonNamingPolicy"/>.
        /// </summary>
        /// <param name="namingStrategy">Newtonsoft naming strategy.</param>
        public NewtonsoftJsonNamingPolicy(NamingStrategy namingStrategy)
        {
            _namingStrategy = namingStrategy;
        }

        /// <inheritdoc />
        public override string ConvertName(string name)
        {
            return _namingStrategy.GetPropertyName(name, false);
        }
    }

Credits

Initial version of this project was based on Mujahid Daud Khan answer on StackOverflow: https://stackoverflow.com/questions/44638195/fluent-validation-with-swagger-in-asp-net-core/49477995#49477995