FluentValidation In Minimal APIs In ASP.NET Core 7.0

namespace FluentValidationInAspCore {
    public class Student {
        public int Id {
            get;
            set;
        }
        public string ? Name {
            get;
            set;
        }
        public int Age {
            get;
            set;
        }
        public double Address {
            get;
            set;
        }
    }
}

Create the StudentValidator class

To implement the required field or other validation to the student Model class, we need to create a StudentValidation class. Here we can create our custom validation by inheriting StudentValidation class from AbstractValidator, like below.

public class StudentValidator: AbstractValidator < Student > {
    public StudentValidator() {
        RuleFor(x => x.Id).NotNull();
        RuleFor(x => x.Name).Length(15);
        RuleFor(x => x.Age).NotNull().InclusiveBetween(5, 20);
        RuleFor(x => x.Address).NotNull().LessThanOrEqualTo(200);
    }
}

Now create an interface IstudentBuilder class and write the below code to add the student information.

public interface IstudentBuilder {
    public void AddStudent(Student student);
}

Now create a studentBuilder class and inherit it from the Istudentbuilder interface and implement the method.

public class StudentBuilder: IstudentBuilder {
    public void AddStudent(Student student) {
        // Write your logic to add data into the database
    }
}

Now we need to register our validator class and builder classes to Program.cs like below

using FluentValidation;
using FluentValidationInAspCore;
var builder = WebApplication.CreateBuilder(args);
// Add services to the container. 
builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddScoped < IValidator < Student > , StudentValidator > ();
builder.Services.AddScoped < IstudentBuilder, StudentBuilder > ();
var app = builder.Build();
// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment()) {
    app.UseSwagger();
    app.UseSwaggerUI();
}
app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();
app.Run();

Create the HttpPost endpoint in the Program.cs

Write the below code to create the HTTP POST endpoint in minimal API.

app.MapPost("/student", async (IValidator < Student > validator, IstudentBuilder builder, Student student) => {
    var validationResult = await validator.ValidateAsync(student);
    if (!validationResult.IsValid) {
        return Results.ValidationProblem(validationResult.ToDictionary());
    }
    builder.AddStudent(student);
    return Results.Created($ "/{student.Id}", student);
});

Now run your application on swagger. Click on the Try it out button.

Without giving any value, if you run it, you will see a validation error like below.

So, these are the step to implement model validation to Minimal API in asp.net core 7.0.