How can I validate a collection of items using Fluent Validation?

How can I validate a collection of items using Fluent Validation?

You can validate a collection by creating a custom validator for the collection type and applying rules to each item.

Can you show me an example of that?

Sure! You can create a validator like this:

public class ItemValidator : AbstractValidator<Item>
{
    public ItemValidator()
    {
        RuleFor(x => x.Name).NotEmpty();
        RuleFor(x => x.Price).GreaterThan(0);
    }
}

public class CollectionValidator : AbstractValidator<List<Item>>
{
    public CollectionValidator()
    {
        RuleForEach(x => x).SetValidator(new ItemValidator());
    }
}

What if I want to add a custom rule for the collection?

You can add custom rules in the CollectionValidator class. For example, you can check if the collection has at least one item:

RuleFor(x => x).NotEmpty().WithMessage("The collection must contain at least one item.");