Introduction
FluentValidation is a .NET library that makes it easy to create validation rules for .NET objects. It provides a fluent interface, which allows developers to write validation logic in a clear and readable way. The library has become popular among developers due to its simplicity and flexibility.
One of the challenges of using FluentValidation is managing the creation and disposal of validator instances. This can be especially difficult if you have a large number of validators, or if your validators have dependencies that need to be injected using dependency injection (DI).
To address this issue, the FluentValidation team has created FluentValidation.DependencyInjectionExtensions, an extension for the FluentValidation library that enables the use of DI to manage the creation and disposal of validator instances. This can make it easier to manage a large number of validators and to inject dependencies into validators using DI.
To use FluentValidation.DependencyInjectionExtensions, you will need to install the NuGet package and configure your DI container to use it. The library is compatible with a variety of DI containers, including Microsoft.Extensions.DependencyInjection and StructureMap. In this article, we will use Microsoft.Extensions.DependencyInjection as an example.
Install the NuGet package
Installing the NuGet package is straightforward. Simply run the following command in the Package Manager Console,
Install-Package FluentValidation.DependencyInjectionExtensions
Configure the DI container
Once the package is installed, you will need to configure your DI container to use it. This can be done in the ConfigureServices method of your Startup class. Here is an example of how to do this,
public void ConfigureServices(IServiceCollection services) {
// Add FluentValidation services
services.AddFluentValidation(config => {
// Add all validators in the current assembly
config.RegisterValidatorsFromAssemblyContaining < Startup > ();
// Alternatively, you can add individual validators manually:
// config.AddValidator<MyValidator>();
});
// Add other services
...
}
The AddFluentValidation method adds FluentValidation services to the DI container. The RegisterValidatorsFromAssemblyContaining method can be used to add all validators in the current assembly to the DI container. Alternatively, you can add individual validators manually using the AddValidator method.
Once the DI container is configured, you can use dependency injection to inject validator instances into your controllers or other classes. Here is an example of how to use a validator to validate a model in a controller action:
Inject validator instances
You can use dependency injection to inject validator instances into your controllers or other classes. Here is an example of how to do this in a controller action,
public class MyController: Controller {
private readonly IValidator < MyModel > _validator;
public MyController(IValidator < MyModel > validator) {
_validator = validator;
}
[HttpPost]
public IActionResult Create(MyModel model) {
var validationResult = _validator.Validate(model);
if (!validationResult.IsValid) {
// Validation failed, return the validation errors to the client
return BadRequest(validationResult.Errors);
}
// Validation succeeded, continue with the request
...
Create custom validators
Custom validators can be created by creating a class that inherits from AbstractValidator<T>. An example of a simple validator that validates a "username" field is provided below,
public class MyValidator: AbstractValidator < MyModel > {
public MyValidator() {
RuleFor(x => x.Username).NotEmpty().WithMessage("Username is required");
RuleFor(x => x.Username).Length(3, 10).WithMessage("Username must be between 3 and 10 characters long");
}
}
You can then register your validator with the DI container using the AddValidator method,
services.AddFluentValidation(config => {
config.AddValidator < MyValidator > ();
});
That's it! You should now be able to use FluentValidation.DependencyInjectionExtensions to manage the creation and disposal of validator instances and to validate models in your .NET applications.
Here are some examples of different types of validation rules that can be created using FluentValidation,
This is a simple validation rule that checks a single property of a model. For example, you might want to ensure that a "username" field is not empty,
RuleFor(x => x.Username).NotEmpty();
This is a validation rule that involves multiple properties of a model, or that uses custom logic to determine whether the rule is valid. For example, you might want to ensure that a password meets certain complexity requirements, such as having at least one uppercase letter, one lowercase letter, and one digit,
RuleFor(x => x.Password)
.Must(p => p.Any(char.IsUpper))
.WithMessage("Password must contain at least one uppercase letter")
.Must(p => p.Any(char.IsLower))
.WithMessage("Password must contain at least one lowercase letter")
.Must(p => p.Any(char.IsDigit))
.WithMessage("Password must contain at least one digit");
This is a validation rule that involves multiple validation checks for a single property. For example, you might want to ensure that a "username" field is not empty and is between 3 and 10 characters long,
RuleFor(x => x.Username)
.NotEmpty()
.Length(3, 10);
Conclusion
FluentValidation is a valuable tool for developers who need to validate .NET objects in their applications. It provides a fluent interface that makes it easy to write clear and readable validation logic. FluentValidation.DependencyInjectionExtensions is an extension of the FluentValidation library that enables the use of dependency injection to manage the creation and disposal of validator instances. This can be particularly useful for managing a large number of validators or for injecting dependencies into validators using DI. The extension is easy to install and configure and can be used to validate models in controllers or other classes using dependency injection. Custom validators can be created by inheriting from AbstractValidator<T>, and can be registered with the DI container using the AddValidator method.