Implementing custom client validation based off of another textbox input

Question

I've been dabbling a little into MVC 5's custom client validation (MVC's GetClientValidationRules and jQuery's validator). I've been able to successfully implement a validator to check whether the user selects a date that is in the past. But what about if I need to check if a user's textbox input is greater than another textbox's input of theirs?

I have it working fine without unobtrusive validation/server-side, but not with unobtrusive validation.

Here's an example.

Model

public Nullable<int> ItemsPurchased
public Nullable<int> ItemsReturned

A custom DataAnnotation has been made for ItemsReturned to check whether its value <= ItemsPurchased. Implementing GetClientValidationRules to actually get ItemsPurchased's current value is where I'm having trouble in the code.

Answer 1

I had a variable in my custom data annotation. I'm not sure why this didn't come to me naturally...but here's my solution.

DataAnnotation (Applied to ItemsReturned)

public string purchasedQuantityField { get; set; }
public ReturnedAttribute(string quantity) {
    purchasedQuantityField = quantity;
}
...
(in GetClientValidationRules)
ModelClientvalidationRule purchaseRule = new ModelClientValidationRule();
purchaseRule.ValidationType = "purchaserestriction";
purchaseRule.ErrorMessage = ErrorMessageString;
purchaseRule.ValidationParameters["otherfield"] = purchasedQuantityField;

Usage in the model:

[Returned("ItemsPurchased", ErrorMessage = "Returned Items cannot be greater than the number of Items Purchased.")]

Then I made my own JS file with the custom client validation rules, CustomClientValidation.js:

jQuery.validator.addMethod("purchaserestriction", function (value, element, params) {
    var purchasedFieldVal = $('input[name="' + params.otherfield + '"]').val();
    if (purchasedFieldVal && value) {
        var returnedVal = parseInt(value);
        var purchasedVal = parseInt(purchasedFieldVal);
        if (returnedVal <= purchasedVal) return true;
        else return false;
    }
);
jQuery.validator.unobtrusive.adapters.add("purchaserestriction", ["otherfield"], function (options) {
    options.rules["purchaserestriction"] = options.params;
    if (options.message) options.messages["purchaserestriction"] = options.message;
});