Validation

Structr.Validation package provides functionality for building strongly-typed validation.

Installation

Validation package is available on NuGet.

dotnet add package Structr.Validation

Setup

Configure validation services:

services.AddValidation(typeof(Program).Assembly);

AddValidation() extension method performs registration of validation provider service and validators implementing IValidator or inherited from Validator class.

Parameter name	Parameter type	Description
assembliesToScan	params Assembly[]	List of assemblies to search validators.
configureOptions	Action<ValidationServiceOptions>	Options to be used by validation service.

Additionally configure IValidationProvider service by specifying it's type and lifetime used ValidationServiceOptions.

Property name	Property type	Description
ProviderServiceType	Type	Changes standard implementation of IValidationProvider to specified one, default is typeof(ValidationProvider).
ProviderServiceLifetime	ServiceLifetime	Specifies the lifetime of an IValidationProvider service, default is Transient.

Usage

Validation objects can be Entities, DTO's, Commands, Queries and many others typed objects.

The basic usage is:

public record UserCreateCommand : IOperation<int>
{
    public string Email { get; init; }
    public string Password { get; init; }
}
public class UserCreateCommandValidator : IValidator<UserCreateCommand>
{
    private readonly IDbContext _dbContext;

    public UserCreateCommandValidator(IDbContext dbContext)
        => _dbContext = dbContext;

    public async Task<ValidationResult> ValidateAsync(UserCreateCommand command, CancellationToken cancellationToken)
    {
        var failures = new List<ValidationFailure>();

        if (string.IsNullOrWhitespace(command.Email))
        {
            failures.Add(new ValidationFailure(nameof(command.Email), command.Email, "Email is required."));
        }
        if (IsValidEmail(command.Email) == false)
        {
            failures.Add(new ValidationFailure(nameof(command.Email), command.Email, "Email is invalid."));
        }
        bool isUniqueEmail = await IsUniqueEmailAsync(command.Email, cancellationToken);
        if (isUniqueEmail == false)
        {
            failures.Add(new ValidationFailure(nameof(command.Email), command.Email, "Email is not unique."));
        }
        if (string.IsNullOrWhitespace(command.Password))
        {
            failures.Add(new ValidationFailure(nameof(command.Password), command.Password, "Password is required."));
        }
        if (IsValidPassword(command.Password) == false)
        {
            failures.Add(new ValidationFailure(nameof(command.Password), command.Password, "Password is invalid."));
        }

        return failures.ToValidationResult();
    }

    private bool IsValidEmail(string email)
    {
        /* Some logic here */
    }

    private async Task<bool> IsUniqueEmailAsync(string email, CancellationToken cancellationToken)
        => await _dbContext.Users.AnyAsync(x => x.Email == email, cancellationToken) == false;

    private bool IsValidPassword(string password)
    {
        /* Some logic here */
    }
}

The last step is to inject IValidationProvider service and use it:

public class UserCreateCommandHandler : IOperationHandler<UserCreateCommand, int>
{
    private readonly IDbContext _dbContext;
    private readonly IValidationProvider _validationProvider;

    public UserCreateCommandHandler(IDbContext dbContext, IValidationProvider validationProvider)
    {
        _dbContext = dbContext;
        _validationProvider = validationProvider;
    }

    public async Task<Guid> HandleAsync(UserCreateCommand command, CancellationToken cancellationToken)
    {
        // Validate incoming command and throw exception if failures.
        await _validationProvider.ValidateAndThrowAsync(command);

        /* Some logic here */
    }
}

Recommendation: For validating Commands/Queries use IOperationFilter instead of calling _validationProvider.ValidateAndThrowAsync() in each command/query. See more details about Operations.

IValidationProvider methods:

Method name	Return type	Description
ValidateAsync	ValidationResult	Asynchronously validates the object and returns the ValidationResult.
ValidateAndThrowAsync	-	Asynchronously validates the object and throws ValidationException if validation result has failures.

ValidationFailure represents a single validation error.

ValidationFailure properties:

Property name	Property type	Description
ParameterName	string	The name of the parameter that caused the failure.
ActualValue	object	The value of the parameter that caused the failure.
Message	string	The message that describes the failure.
Code	string	The optional failure code.
Level	ValidationFailureLevel	The optional level of failure - Error, Warning or Info. Default value is Error.

ValidationResult represents all failures that occur during validation execution.

ValidationResult properties:

Property name	Property type	Description
IsValid	bool	Returns true if the validation result has not failures, otherwise false.

ValidationResult class inherits from IEnumerable<ValidationFailure> and allow you to use iteration:

ValidationResult validationResult = await _validationProvider.ValidateAsync(command);
if (validationResult.IsValid == false)
{
    foreach(ValidationFailure validationFailure in validationResult)
    {
        _logger.LogError(validationFailure.Message);
    }
}

Thrown ValidationException class has following main properties:

Property name	Property type	Description
ValidationResult	ValidationResult	The result of validation.
Message	string	The messages of all failures joined into one string.

try
{
    await _validationProvider.ValidateAsync(command);
}
catch(ValidationException ex)
{
    // Option 1 - Use default exception message property:
    _logger.LogError(ex.Message);

    // Option 2 - Iterate all failures with message:
    foreach(ValidationFailure validationFailure in ex.ValidationResult)
    {
        _logger.LogError(validationFailure.Message);
    }
}