Data Validation in .NET Core API with Fluent Validation: Best Practices and Examples

Fluent Validation is a powerful and flexible validation library for .NET Core API applications. It provides an easy-to-use and fluent interface for validating complex business rules and data constraints. In this blog post, we’ll walk through a step-by-step process of using Fluent Validation in .NET Core API and solve a fun and complex business problem.

Let’s begin with a brief overview of Fluent Validation.

Fluent Validation is a .NET library that allows you to define validation rules for your models in a fluent way. With Fluent Validation, you can easily define validation rules for properties, model-level validation, and complex business rules.

Now, let’s dive into a complex business problem and see how we can solve it using Fluent Validation.

Imagine we are building a food ordering system. In this system, customers can order different types of food items, such as pizza, burgers, and sandwiches. Each food item has its own set of rules and constraints. For example, a pizza can have a maximum of 5 toppings, while a sandwich cannot have any toppings. Additionally, we need to validate the customer’s address and ensure that it is valid.

To solve this problem, we’ll use Fluent Validation. Let’s start by creating a new .NET Core API project.

Step 1: Install the Fluent Validation NuGet package

To use Fluent Validation, we need to install the FluentValidation.AspNetCore NuGet package. You can do this by opening the NuGet Package Manager in Visual Studio and searching for “FluentValidation.AspNetCore”. Once you’ve found the package, click on “Install” to install it in your project.

Step 2: Create a food order model

Next, we need to create a food order model that represents the customer’s order. Here’s what our food order model might look like:

public class FoodOrder
{
    public string Type { get; set; }
    public List<string> Toppings { get; set; }
    public string BreadType { get; set; }
    public string Address { get; set; }
}

Step 3: Create a validator for the food order model

Now that we have our food order model, we need to create a validator for it. The validator will define the…