Conditional validation

Related to my recent post about cascading drop down lists, I needed to do some conditional validation based on a drop down list selection. I found a great post on Simon Ince’s blog about conditional validation in MVC 3. He even has a new project to wrap up some of the conditional functionality that he blogged about, but I decided to roll my own since I would learn more going that route.

Using the project attached to his post, I started dissecting what he was doing. After a while, I got the client validation working, but I realized I was so focused on the client/server validation piece that I did not get my conditions correct! After a few tweaks, I finally got everything working. Here is the custom attribute:

public class ConditionalMaximumWeightAttribute : ValidationAttribute, 
                                                 IClientValidatable {

    private const string ERRORMSG = "Weight must not exceed {0} lbs.";

    public string DependentProperty { get; set; }
    public string DependentValue { get; set; }
    public int MaximumWeight { get; set; }

    public ConditionalMaximumWeightAttribute(string dependentProperty, 
                                             string dependentValue, 
                                             int maximumWeight) {
        this.DependentProperty = dependentProperty;
        this.DependentValue = dependentValue;
        this.MaximumWeight = maximumWeight;
    }

    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(
                         ModelMetadata metadata, ControllerContext context) {
        var rule = new ModelClientValidationRule() {
            ErrorMessage = String.Format(ERRORMSG, this.MaximumWeight),
            ValidationType = "maximumweight",
        };

        string depProp = BuildDependentPropertyId(metadata, context 
                                                            as ViewContext);

        rule.ValidationParameters.Add("dependentproperty", depProp);
        rule.ValidationParameters.Add("dependentvalue", this.DependentValue);
        rule.ValidationParameters.Add("weightvalue", this.MaximumWeight);

        yield return rule;
    }

    protected override ValidationResult IsValid(object value, 
                                        ValidationContext validationContext) {
        // get a reference to the property this validation depends upon
        var containerType = validationContext.ObjectInstance.GetType();
        var field = containerType.GetProperty(this.DependentProperty);

        if (field != null) {
            // get the value of the dependent property
            var dependentvalue = 
                field.GetValue(validationContext.ObjectInstance, null);

            var weight = 
                containerType.GetProperty(validationContext.DisplayName);
            int weightvalue = 
                (int)weight.GetValue(validationContext.ObjectInstance, null);

            // compare the value against the target value
            if (dependentvalue == this.DependentValue && 
                                  weightvalue > this.MaximumWeight) {
                // validation failed - return an error
                return new ValidationResult(String.Format(ERRORMSG, 
                                            this.MaximumWeight));
            }
        }

        return ValidationResult.Success;
    }

    private string BuildDependentPropertyId(ModelMetadata metadata, 
                                            ViewContext viewContext) {
        // build the ID of the property
        string depProp = viewContext.ViewData.TemplateInfo
                         .GetFullHtmlFieldId(this.DependentProperty);
        // unfortunately this will have the name of the current field appended 
        // to the beginning,
        // because the TemplateInfo's context has had this fieldname appended 
        // to it. Instead, we
        // want to get the context as though it was one level higher (i.e. 
        // outside the current property,
        // which is the containing object (our Person), and hence the same 
        // level as the dependent property.
        var thisField = metadata.PropertyName + "_";
        if (depProp.StartsWith(thisField))
            // strip it off again
            depProp = depProp.Substring(thisField.Length);
        return depProp;
    }
}

Gist

To put this in context, I need to restrict a maximum weight allowed for a carrier. At a certain point, we may as well go with another carrier because it is cheaper. However, I don’t want to restrict the maximum weight if the carrier that has been selected is the cheaper carrier.

The attribute is used like so, where PropertyName is the name of the related property to check, PropertyValue is the conditional value of the property, and MaximumWeight is an integer representing the maximum weight for the conditional:

public class ...

    [ConditionalMaximumWeight("PropertyName", "PropertyValue", MaximumWeight)]
    [Required(ErrorMessage = "Weight required")]
    public int? Weight { get; set; }

    ...
}

Here is the client-side implementation:

<script type="text/javascript">
    $.validator.addMethod("maximumweight",
        function (value, element, parameters) {
            var carrier = $("#" + parameters["dependentproperty"]).val();
            var carriervalue = parameters["dependentvalue"].toString();
            var weightvalue = Number(parameters["weightvalue"]);
            if (carrier == carriervalue && value > weightvalue) {
                return false;
            }
            return true;
        }
    );

    $.validator.unobtrusive.adapters.add(
    "maximumweight",
    ["weightvalue", "dependentproperty", "dependentvalue"],
    function (options) {
        options.rules["maximumweight"] = {
            weightvalue: options.params["weightvalue"],
            dependentproperty: options.params["dependentproperty"],
            dependentvalue: options.params["dependentvalue"]
        };
        options.messages["maximumweight"] = options.message;
    });
</script>

Gist

I should probably do a little null checking in on the client-side, but I may just find that out the hard way! 🙂

ASP.NET MVC Cascading drop down lists

Found this great post on how to create cascading drop downs in ASP.NET MVC.

I created a page for looking up shipping rates by carrier, weight and zip code. For my particular usage, I had 2 lists: Carrier and ShipMethod. I wanted the cascading list to be disabled when the initial list selection had yet to be made. I created functions to populate the target list as well as enable/disable the target list. I made the js into a reusable Razor helper which should allow me to use it anywhere I need this functionality.

Here is the helper code:

@helper DynamicDropDowns() {
<script type="text/javascript">
    function listChanged($list, $target, url) {
        var listId = $list.val();
        if (listId == "") { // User selected first option, 
                            // so clear and disable the list
            $target.empty();
            enableList($target, false);
            return;
        }
        $.getJSON(url, { id: listId }, function (data) {
            $target.empty(); // Clear the list
            $.each(data, function (idx, item) { // Add the data
                $target.append($("<option/>",
                {
                    value: item.Value,
                    text: item.Text
                }));
            });
            enableList($target, true); // Enable the list
        });
    }

    function enableList($list, enabled) {
        $list.attr("disabled", enabled ? null : "disabled");
    }
</script>
}

Gist

And here it is in action:

<script type="text/javascript">
    $(function () {
        var $carrier = $("#Carrier");
        var $ship = $("#ShipMethod");
        enableList($ship, false);
        $carrier.change(function () {
            listChanged($(this), $ship, "/Tools/GetShipMethodsByCarrier");
        });
    });
</script>

SignalR

I first heard about SignalR on Scott Hanselman’s blog. He showed an example webchat app in 12 lines of code. It looked pretty cool, but I did not make the time to take a deeper look.

I was just watching the Tekpub Full Throttle episode with Ayende and that led me to Ayande’s blog, where I saw his post “How SignalR killed RavenMQ.”

So, here is my link to the Github project. My personal reminder to make the time to check out SignalR.

Project Github link: SignalR

CSS3 Gradient Buttons

I was doing some style updates for our CCNET server after switching to the liquidBlue theme (why is that not the default theme?) and I wanted some nicer buttons. I did a quick search and found this great article. It provides a bunch of color templates, though none of them seemed to quite match the color palette so I just opted to forgo the gradient in the button. Maybe when I have some more time I’ll take a crack at figuring out the colors for the gradients.

Automated Nuget package creation

We have some core libraries that a lot of other libraries depend on. While these change very infrequently, they were written a while ago and some refactoring is in order. The problem is I don’t want to have to doa lot of manual updating. I thought I’d look into automating Nuget packages.

The article has sample scripts which I’ll be able to adapt and setup to generate Nuget packages on build. I can then copy the packages to a local Nuget server ad then I’ll be able to set up the other libraries to use Nuget so they can easily get any future updates!

Remote Desktop auto disconnect and logoff

From http://www.howtonetworking.com/casestudy/tstimelimit1.htm

To set time limits for automatically disconnecting or logging-off a user from a remote desktop session:

  1. Open group Policy by running gpedit.msc.
  2. Select Administrative Templates > Windows Components > Terminal Services > Sessions.
    In Windows 2008: Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Session Host > Session Time Limits.
  3. Right-click on Set time limit for disconnected sessions.
  4. Select Properties.
  5. Check Enable and select time you want under End a disconnected session.