如何在验证方法中区分编辑和创建新项目？

Question

I'm trying to ensure that each item in my cms has a unique url.

The model has been made an IValidatableObject and I am using the validation method below.

The trouble I'm having is discerning whether the item is being created (url must not match any existing items) or edited (url must not match any item other than itself ).

How can I do this... and am I even approaching this the right way?

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        DataContext db = new DataContext();
        string itemContainingURL = db.CMSPages.Where(c => c.URL == URL).Select(c => c.Title).SingleOrDefault();
        if (!string.IsNullOrEmpty(itemContainingURL))
        {
            yield return new ValidationResult(String.Format("URL should be unique, but it already exists for item: {0}", itemContainingURL), new[] { "URL" });
        }

    } 

Answer 1

Does it matter? Just test existence of an item of differing ID that shares the URL, and you can cover both cases.

Example pseudocode:

bool IsUnique()
{
    return !repository.Any(x => x.ID != this.ID && x.URL == this.URL);
}