Fluent Validation with Swagger in Asp.net Core

Question

I am currently using Fluent Validation instead of Data Annotations for my Web api and using swagger for API documentation. Fluent validation rules are not reflected in swagger model as i am unable to configure fluent validation rules with swagger schema filter.

This Blog has a good explanation for using it with ASP.net MVC. but i am unable to configure it to use it in ASP.net Core.

So far i have tried the following code but i am unable to get validator type.

services.AddSwaggerGen(options => options.SchemaFilter<AddFluentValidationRules>());

public class AddFluentValidationRules : ISchemaFilter
{
    public void Apply(Schema model, SchemaFilterContext context)
    {
        model.Required = new List<string>();
        var validator = GetValidator(type); // How?
        var validatorDescriptor = validator.CreateDescriptor();

        foreach (var key in model.Properties.Keys)
        {
            foreach (var propertyValidator in validatorDescriptor.GetValidatorsForMember(key))
            {
                 // Add to model properties as in blog
            }
        }
    }
}

Answer 1

I've created github project and nuget package based on Mujahid Daud Khan answer. I made redesign to support extensibility and supported other validators.

github: https://github.com/micro-elements/MicroElements.Swashbuckle.FluentValidation

nuget: https://www.nuget.org/packages/MicroElements.Swashbuckle.FluentValidation

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

Supported validators

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

Usage

1. Reference packages in your web project:

<PackageReference Include="FluentValidation.AspNetCore" Version="7.5.2" />
<PackageReference Include="MicroElements.Swashbuckle.FluentValidation" Version="0.4.0" />
<PackageReference Include="Swashbuckle.AspNetCore" Version="2.3.0" />

2. Change Startup.cs

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
    services
        .AddMvc()
        // Adds fluent validators to Asp.net
        .AddFluentValidation(fv => fv.RegisterValidatorsFromAssemblyContaining<CustomerValidator>());

    services.AddSwaggerGen(c =>
    {
        c.SwaggerDoc("v1", new Info { Title = "My API", Version = "v1" });
        // Adds fluent validation rules to swagger
        c.AddFluentValidationRules();
    });
}

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

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

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 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);
    }
}

Feel free to add issues!

Answer 2

After searching i have finally figured out that i needed to IValidationFactory for validator instance.

public class AddFluentValidationRules : ISchemaFilter
{
    private readonly IValidatorFactory _factory;

    /// <summary>
    ///     Default constructor with DI
    /// </summary>
    /// <param name="factory"></param>
    public AddFluentValidationRules(IValidatorFactory factory)
    {
        _factory = factory;
    }

    /// <summary>
    /// </summary>
    /// <param name="model"></param>
    /// <param name="context"></param>
    public void Apply(Schema model, SchemaFilterContext context)
    {

        // use IoC or FluentValidatorFactory to get AbstractValidator<T> instance
        var validator = _factory.GetValidator(context.SystemType);
        if (validator == null) return;
        if (model.Required == null)
            model.Required = new List<string>();

        var validatorDescriptor = validator.CreateDescriptor();
        foreach (var key in model.Properties.Keys)
        {
            foreach (var propertyValidator in validatorDescriptor
                .GetValidatorsForMember(ToPascalCase(key)))
            {
                if (propertyValidator is NotNullValidator 
                  || propertyValidator is NotEmptyValidator)
                    model.Required.Add(key);

                if (propertyValidator is LengthValidator lengthValidator)
                {
                    if (lengthValidator.Max > 0)
                        model.Properties[key].MaxLength = lengthValidator.Max;

                    model.Properties[key].MinLength = lengthValidator.Min;
                }

                if (propertyValidator is RegularExpressionValidator expressionValidator)
                    model.Properties[key].Pattern = expressionValidator.Expression;

                // Add more validation properties here;
            }
        }
    }

    /// <summary>
    ///     To convert case as swagger may be using lower camel case
    /// </summary>
    /// <param name="inputString"></param>
    /// <returns></returns>
    private static string ToPascalCase(string inputString)
    {
        // If there are 0 or 1 characters, just return the string.
        if (inputString == null) return null;
        if (inputString.Length < 2) return inputString.ToUpper();
        return inputString.Substring(0, 1).ToUpper() + inputString.Substring(1);
    }
}

and add this class to swaggerGen options

options.SchemaFilter<AddFluentValidationRules>();

Answer 3

1. Install Nuget package: MicroElements.Swashbuckle.FluentValidation

2. Add to ConfigureServices: services.AddFluentValidationRulesToSwagger();