ASP.NET MVC 3 client-side validation with parameters

You could use the ValidationParameters property to add custom parameters to the rule:

public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
{
    var rule = new ModelClientValidationRule
    {
        ErrorMessage = this.ErrorMessage,
        ValidationType = "futuredate",
    };
    rule.ValidationParameters.Add("param1", "value1");
    rule.ValidationParameters.Add("param2", "value2");
    yield return rule;
}

which could be used in the adapter:

jQuery.validator.unobtrusive.adapters.add(
    'futuredate', 
    [ 'param1', 'param2' ],
    function (options) {
        var param1 = options.params.param1; // shall equal 'value1'
        var param2 = options.params.param2; // shall equal 'value2'
        // TODO: use those custom parameters to define the client rules
    }
);

---

UPDATE:

As requested in the comments section here’s how you could pass those parameters to the custom validator rule function:

jQuery.validator.unobtrusive.adapters.add(
    'futuredate', 
    [ 'param1', 'param2' ],
    function (options) {
        // simply pass the options.params here
        options.rules['greaterThan'] = options.params;
        options.messages['greaterThan'] = options.message;
    }
);

jQuery.validator.addMethod('greaterThan', function (value, element, params) {
    // params here will equal { param1: 'value1', param2: 'value2' }
    return ...
}, '');