Fluent Validation C# Unique Id in collection

Question

I have an entity that has a nested collection as a property which I will receive from a front-end application.

I just want to make sure that each item in this collection(ICollection ChildClassCollection) has a unique Id within the model I have received.

I am using FluentValidation and would like to add this validation using it too for consistency.

It's something very simple I couldn`t find an elegant way to solve..

An example:

public class ParentClass
{
    public string Name { get; set; }

    public ICollection<ChildClass> ChildClassCollection { get; set; }
}

public class ChildClass
{
    public int Id { get; set; }

    public string Name { get; set; }
}

Answer 1

Here is what I ended up with: PRetty cleand, plus, when it encounters issue, it will exit

           this.RuleFor(or => or.ChildClassCollection)
               .Must(this.IsDistinct)
               .WithMessage("There are more than one entity with the same Id");

        public bool IsDistinct(List<UpdateRoleDTO> elements)
        {
            var encounteredIds = new HashSet<int>();

            foreach (var element in elements)
            {
                if (!encounteredIds.Contains(element.Id))
                {
                   encounteredIds.Add(element.Id);
                }
                else
                {
                    return false;
                }
            }

            return true;
       }