abp-validation

ABP Validation Skill

Trigger

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

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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.

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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

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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.

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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

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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

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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"]
      }
    ]
  }
}

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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

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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

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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]

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Related

• Exception Handling — How validation errors are handled
• FluentValidation — External validation library docs
• ASP.NET Core Validation — Microsoft's validation documentation