MVC3 class validation attributes

I am creating a site for a silent auction. My class has a CurrentBidAmount pro开发者_运维百科perty, and a SuggestedBidAmount property. The SuggestedBidAmount is basically the current bid amount plus the current minimum bid increment. (So the current bid is $10, and the bid increment is $5, then the suggested bid is $15). When the bidder enters a new bid value, I want to validate that the new value is at least as much as the SuggestedBidAmount or greater.

I want to enforce this at the class level. The problem is, I'm not sure of what the validation attribute tags are, and can't seem to find them on Google. I must be using the wrong search terms, nonetheless, I can't find them.

The [Compare] tag is close, but that does a verbatim compare. I basically need to compare one property against another, and verify that it is equal to or greater than the other property.

Can anyone please point me in the right direction?

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You can create your own custom validation attribute and just override its IsValid method:

    [AttributeUsage(AttributeTargets.Class)]
    public class BidCompareAttribute : ValidationAttribute
    {
        public string CurrentBidPropertyName { get; set; }
        public string MinBidIncrementPropertyName { get; set; }

        public override bool IsValid(object value)
        {
            var properties = TypeDescriptor.GetProperties(value);
            var minBidIncrement = properties.Find("MinBidIncrement", true).GetValue(value) as IComparable;
            var currentBid = properties.Find("CurrentBid", true).GetValue(value) as IComparable;
            return currentBid.CompareTo(minBidIncrement) >= 0;
        }
    }

Than use it like this:

    [BidCompare(CurrentBidPropertyName = "CurrentBid", 
                MinBidIncrementPropertyName = "MinBidIncrement")]
    public class BidModel
    {
        public int CurrentBid { get; set; }    
        public int MinBidIncrement { get; set; }
    }