Validation

Validation system is used to validate the user input or client request for a particular controller action or service method.

ABP is compatible with the ASP.NET Core Model Validation system and everything written in its documentation is already valid for ABP based applications. So, this document mostly focuses on the ABP features rather than repeating the Microsoft documentation.

In addition, ABP adds the following benefits:

• Defines IValidationEnabled to add automatic validation to an arbitrary class. Since all the application services inherently implements it, they are also validated automatically.
• Automatically localize the validation errors for the data annotation attributes.
• Provides extensible services to validate a method call or an object state.
• Provides FluentValidation integration.

Validating DTOs

This section briefly introduces the validation system. For details, see the ASP.NET Core validation documentation.

Data Annotation Attributes

Using data annotations is a simple way to implement the formal validation for a DTO in a declarative way. Example:

public class CreateBookDto
{
    [Required]
    [StringLength(100)]
    public string Name { get; set; }

    [Required]
    [StringLength(1000)]
    public string Description { get; set; }

    [Range(0, 999.99)]
    public decimal Price { get; set; }
}

When you use this class as a parameter to an application service or a controller, it is automatically validated and a localized validation exception is thrown (and handled by the ABP framework).

IValidatableObject

IValidatableObject can be implemented by a DTO to perform custom validation logic. CreateBookDto in the following example implements this interface and checks if the Name is equals to the Description and returns a validation error in this case.

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace Acme.BookStore
{
    public class CreateBookDto : IValidatableObject
    {
        [Required]
        [StringLength(100)]
        public string Name { get; set; }

        [Required]
        [StringLength(1000)]
        public string Description { get; set; }

        [Range(0, 999.99)]
        public decimal Price { get; set; }

        public IEnumerable<ValidationResult> Validate(
            ValidationContext validationContext)
        {
            if (Name == Description)
            {
                yield return new ValidationResult(
                    "Name and Description can not be the same!",
                    new[] { "Name", "Description" }
                );
            }
        }
    }
}

Resolving a Service

If you need to resolve a service from the dependency injection system, you can use the ValidationContext object. Example:

var myService = validationContext.GetRequiredService<IMyService>();

While resolving services in the Validate method allows any possibility, it is not a good practice to implement your domain validation logic in DTOs. Keep DTOs simple. Their purpose is to transfer data (DTO: Data Transfer Object).

Validation Infrastructure

This section explains a few additional services provided by the ABP framework.

IValidationEnabled Interface

IValidationEnabled is an empty marker interface that can be implemented by any class (registered to and resolved from the DI) to let the ABP framework perform the validation system for the methods of the class. Example:

using System.Threading.Tasks;
using Volo.Abp.DependencyInjection;
using Volo.Abp.Validation;

namespace Acme.BookStore
{
    public class MyService : ITransientDependency, IValidationEnabled
    {
        public virtual async Task DoItAsync(MyInput input)
        {
            //...
        }
    }
}

ABP framework uses the dynamic proxying / interception system to perform the validation. In order to make it working, your method should be virtual or your service should be injected and used over an interface (like IMyService).

AbpValidationException

Once ABP determines a validation error, it throws an exception of type AbpValidationException. Your application code can throw AbpValidationException, but most of the times it is not needed.

• ValidationErrors property of the AbpValidationException contains the validation error list.
• Log level of the AbpValidationException is set to Warning. It logs all the validation errors to the logging system.
• AbpValidationException is automatically caught by the ABP framework and converted to a usable error into with HTTP 400 status code. See the exception handling document for more.

Advanced Topics

IObjectValidator

In addition to the automatic validation, you may want to manually validate an object. In this case, inject and use the IObjectValidator service:

• Validate method validates the given object based on the validation rules and throws an AbpValidationException if it is not in a valid state.
• GetErrors doesn't throw an exception, but only returns the validation errors.

IObjectValidator is implemented by the ObjectValidator by default. ObjectValidator is extensible; you can implement IObjectValidationContributor interface to contribute a custom logic. Example:

public class MyObjectValidationContributor
    : IObjectValidationContributor, ITransientDependency
{
    public void AddErrors(ObjectValidationContext context)
    {
        //Get the validating object
        var obj = context.ValidatingObject;

        //Add the validation errors if available
        context.Errors.Add(...);
    }
}

• Remember to register your class to the DI (implementing ITransientDependency does it just like in this example)
• ABP will automatically discover your class and use on any type of object validation (including automatic method call validation).

IMethodInvocationValidator

IMethodInvocationValidator is used to validate a method call. It internally uses the IObjectValidator to validate objects passes to the method call. You normally don't need to this service since it is automatically used by the framework, but you may want to reuse or replace it on your application in rare cases.

FluentValidation Integration

Volo.Abp.FluentValidation package integrates the FluentValidation library to the validation system (by implementing the IObjectValidationContributor). See the FluentValidation Integration document for more.