abp-validation

ABP Validation Skill

Trigger

User asks about validation, DTO validation, FluentValidation, IValidatableObject, validation errors, AbpValidationException, or input validation in ABP Framework.

Core Concepts

ABP provides automatic validation for application service inputs using:

1. Data Annotation Attributes — Declarative validation on DTOs
2. IValidatableObject — Custom validation logic in DTOs
3. FluentValidation — External validator classes
4. IValidationEnabled — Enable validation on any DI-registered service

Validation errors are automatically caught and returned as standardized error responses.

Data Annotation Validation

Basic Usage

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; }
}

• Automatically validated when used as application service/controller parameter
• Localized validation exception thrown and handled by ABP
• Common attributes: Required, StringLength, Range, EmailAddress, RegularExpression, MinLength, MaxLength

IValidatableObject

Custom Validation in DTOs

public class CreateBookDto : IValidatableObject
{
    public string Name { get; set; }
    public decimal Price { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        var results = new List<ValidationResult>();

        if (Price <= 0)
        {
            results.Add(new ValidationResult(
                "Price must be greater than zero.",
                new[] { nameof(Price) }
            ));
        }

        if (string.IsNullOrWhiteSpace(Name))
        {
            results.Add(new ValidationResult(
                "Name cannot be empty.",
                new[] { nameof(Name) }
            ));
        }

        return results;
    }
}

Resolving Services in Validate

public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
    var myService = validationContext.GetRequiredService<IMyService>();
    // Use service for validation logic
    // ...
}

Warning: Resolving services in Validate is possible but not recommended. Keep DTOs simple — they should transfer data, not contain domain validation logic.

FluentValidation Integration

Installation

abp add-package Volo.Abp.FluentValidation

Or manually:

dotnet add package Volo.Abp.FluentValidation

Add module dependency:

[DependsOn(typeof(AbpFluentValidationModule))]
public class MyModule : AbpModule { }

Usage

public class CreateUpdateBookDtoValidator : AbstractValidator<CreateUpdateBookDto>
{
    public CreateUpdateBookDtoValidator()
    {
        RuleFor(x => x.Name).Length(3, 10);
        RuleFor(x => x.Price).ExclusiveBetween(0.0f, 999.0f);
        RuleFor(x => x.Description).NotEmpty().MaximumLength(1000);
    }
}

• ABP auto-discovers validator classes
• Automatically associated with the DTO type
• Can be placed in the same project as the DTO

Validation Infrastructure

IValidationEnabled Interface

Enable validation on any DI-registered service:

public class MyService : ITransientDependency, IValidationEnabled
{
    public virtual async Task DoItAsync(MyInput input)
    {
        // input is automatically validated
    }
}

Requirements:

• Method must be virtual OR service used via interface
• Class must be registered in DI (implements ITransientDependency, ISingletonDependency, or IScopedDependency)

Enabling/Disabling Validation

public class MyService : ITransientDependency, IValidationEnabled
{
    public bool IsValidationEnabled { get; set; } = true; // Default

    public virtual async Task DoItAsync(MyInput input) { }
}

AbpValidationException

Thrown automatically when validation fails:

public class AbpValidationException : AbpException, IHasValidationErrors
{
    public IList<ValidationResult> ValidationErrors { get; }
}

• Implements IHasValidationErrors — errors serialized in API response
• Automatically handled by ABP's exception handler
• Returns HTTP 400 with validation error details

Validation Error Response Format

{
  "error": {
    "code": "App:010046",
    "message": "Your request is not valid, please correct and try again!",
    "validationErrors": [
      {
        "message": "Username should be minimum length of 3.",
        "members": ["userName"]
      },
      {
        "message": "Password is required",
        "members": ["password"]
      }
    ]
  }
}

Best Practices

1. Use Data Annotations for simple, declarative validation (required, length, range)
2. Use FluentValidation for complex validation rules, cross-property validation
3. Use IValidatableObject sparingly — only when validation is tightly coupled to the DTO
4. Keep domain validation in domain services, not in DTOs
5. Enable validation on application services — they are validated by default
6. Use IValidationEnabled on custom services that need input validation
7. Methods must be virtual for interception-based validation to work
8. Localize validation messages using resource files for multi-language support

Validation + Exception Handling Flow

Client Request
    ↓
DTO Deserialization
    ↓
ABP Validation Interceptor
    ↓ (if invalid)
AbpValidationException thrown
    ↓
ABP Exception Handler
    ↓
HTTP 400 + validationErrors JSON
    ↓
Client receives structured error

Common Validation Attributes Reference

| Attribute | Purpose | Example | |---|---|---| | [Required] | Non-null, non-empty | [Required] public string Name { get; set; } | | [StringLength(max)] | Max length | [StringLength(100)] | | [StringLength(min, max)] | Min/max length | [StringLength(3, 100)] | | [Range(min, max)] | Numeric range | [Range(0, 999.99)] | | [EmailAddress] | Email format | [EmailAddress] | | [RegularExpression(pattern)] | Regex match | [RegularExpression(@"^[a-zA-Z]+$")] | | [MinLength(n)] | Minimum collection/string length | [MinLength(3)] | | [MaxLength(n)] | Maximum collection/string length | [MaxLength(100)] | | [Url] | URL format | [Url] | | [Phone] | Phone format | [Phone] |

Related

• [Exception Handling](../abp-exception-handling/SKILL.md) — How validation errors are handled
• FluentValidation — External validation library docs
• ASP.NET Core Validation — Microsoft's validation documentation