Question

I’m pretty new to MVC3 and I’ve started work on a newish jQuery / MVC3 / EF 4.1 code first project and have been going over some of the existing code. One part of the code retrieves values from the db via a Controller action when ever the value of a certain drop down changes (SubtypeID.change event). Here’s the jQuery:

    $.getJSON(
    "/StudyDesign/GetSubtypes?typeId=" + typeId,
    function (data) {
        var theDropDown = document.getElementById("SubtypeID");

        if (data.length === 0) {
            theDropDown.disabled = true;
        }

        $.each(data, function () {
            $("#SubtypeID").append($('<option>').attr('value', this.SubtypeID).text(this.Name));
        });
    }
);

And here’s the Controller Action:

    [OutputCache(Duration = int.MaxValue, VaryByParam = "typeId", Location = OutputCacheLocation.Server)]
    public JsonResult GetSubtypes(int typeId)
    {
        var studyType = this._studyDesignRepository.StudyTypes.SingleOrDefault(s => s.StudyTypeID == typeId);
        return studyType == null ? this.Json(new List<Subtype>()) : this.Json(studyType.Subtypes.Select(s => new { s.SubtypeID, s.Name }).ToList(), JsonRequestBehavior.AllowGet);
    }

This works fine, but in our Controller constructor we have a lot of code that retrieves different values from the db that populate other dropdowns and grids etc. Once the page is loaded the first time we don’t need to to get these values again as they are already in the page, but every time the .change event is fired and StudyDesign/GetSubtypes is called, the Controller constructor runs and does all the db calls again. This seems unnecessary so I’m wondering

• is there a better way to do this?
• can/should we retrieve the json data a different way?
• should we have the json Actions / methods in a separate Controller?

Thanks in advance 🙂

Answer 1

In general, it’s a really bad idea to do a bunch of initialization like that in your controllers constructor. For starters, there’s no guarantee that this data will be there from call to call because the stateless nature of the app may cause the controller to get destroyed between calls. This means doing all your expensive work up front all the time.

You should do that expensive work in your Action method, with the cacheing you’re using, those methods won’t get called again until the cache times out.

Upon re-reading, it sounds like you’re talking about other data that gets populated on the page, but never gets changed because you’re doing Ajax calls. In that case, my point still stands. Do it in your action method for the page, rather than the constructor. then it will only load that data when you actually retrieve a page.