Implementing complex validation logic with IValidateObject

In this recipe, we will implement custom validation logic in our DTO class using IValidateObject. This will allow us to create validation logic for an entire model instead of only one property.

Getting ready

The starting code for this project resides here: https://github.com/PacktPublishing/ASP.NET-9-Web-API-Cookbook/tree/main/start/chapter02/IValidateObject.

How to do It…

1. Modify your existing EventRegistrationDTO to inherit from IValidateObject:

   using System;
   using System.Collections.Generic;
   using System.ComponentModel.DataAnnotations;
   namespace events.Models
   {
       public class EventRegistrationDTO : IValidatableObject
       {
       …

2. Create the Validate method, which yields a ValidationResult if the date is not in the future:

   public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
       ...