MS Mvc

Lazy list

Sean Lynch — Wed, 21 May 2008 12:34:18 GMT

I have been following Rob Conery's posts on the MVC Storefront, and trying the repository/pipes-filters for data access that he has been using.

While trying out the implementation of a LazyList he was using, I had noticed that the example table was being joined onto the category table. At the time however, I really had not thought much of it, until I read MVC Storefront: Brainbender Intermission which got me thinking.

Admittedly, I don't really have to much of a problem with it loading all of the examples for all the categories at one time at the moment. However, I figured it would be nice to have it work the way intended, and query the database for the examples in a category only when asked for.

I liked the idea of the LazyList, and since I was already using a Service class for all data access, along with setting up the category hierarchy I moved the creation of the LazyList of examples property into the the GetCategories method of the service class.

It seems that as long as the LazyList is created after the categories .ToList() call it properly works. So I ended up with this code:

            categories.ForEach(category =>
            {
                category.Examples =
                    new LazyList
                        <DevExamples.Data.Example>(
                        from e in repository.GetExamples()
                        where e.CategoryId == category.ID
                        select e);

                var subCategories = (from sub in categories
                                     where sub.ParentId == category.ID
                                     select sub).ToList();
                category.SubCategories = subCategories;

                subCategories.ForEach(c => c.Parent = category);

            });

Technorati Tags: aspnetmvc

ABCs scare me

Sean Lynch — Fri, 22 Feb 2008 17:29:07 GMT

I had a whole post about this, in my mind, but as I was typing, I kept poking holes in my points as to why I hope that in the end IHttpContext stays around.

However, since am trying get into the habit of actually sleeping at night I'm just going to put a couple of sentences in.

In Abstract Base Classes Have Versioning Problems Too Haacked gave an example that of a problem with ABCs, that at some point later a virtual method would be added, and throw a not implemented exception. This in itself seems to be a breaking change to me, its just a matter of where it breaks.

Now instead of stopping my program from working if an ISV's customer decides to run it on the new framework. It will fail in some completely unexpected way, causing extra support calls, and possibly causing sever side effects.

So while I am all for putting the ball in the developers court, putting the ball in my customers court scares the crap out of me. And that is essentially what I see using an abstract base classes to allow for extensibility and then adding virtual methods, since they cannot be actual abstract methods or we are in the same boat as interfaces, that throw not implemented exceptions does.

Technorati Tags: Microsoft MVC

Got my nice Urls working

Sean Lynch — Mon, 24 Dec 2007 15:44:26 GMT

Its amazing how fast things can be done when not fighting bad assumptions. In this case it was that my admin URLs needed to use the nice descriptive URLs, instead of just /[Controller]/[Action]/[id] type routing.

Once I realized I was making things overly complicated I, I ended up with a set of routing functions that are actually a bit less complicated then what I would have come up with if I had been able to extend the RouteTable the way I had planned originally.

I also decided that I didn't like the idea of having the make every category and example name unique. Most of this was that I'm not the creative, but I also realized that it would be really ugly I wanted to have namespaces as categories. For example, it would not have been possible to have both C/System/Windows/Forms/Control and C/System/Web/UI/Control since Control would have had to be unique.

I also decided that I was going to set a limit to the depth of categories that the site was going to have, though it is easy to update this. First I made a function that would generate routes similar to those previously posted.

protected void CreateRouteSet(string baseRoute, string baseName
    , int maxDepth, object Defaults)
{
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < maxDepth; i++)
    {
        if (sb.Length > 0)
            sb.Append("/");

        sb.AppendFormat("[{0}{1}]", baseName, i);

        RouteTable.Routes.Add(new Route{
         
            Url = String.Format(baseRoute,sb.ToString()),
            Defaults = Defaults,
            RouteHandler = typeof(MvcRouteHandler)
        });
    }
}

protected void Application_Start(object sender, EventArgs e)
{

    CreateRouteSet("C/{0}", "Category", 6,
        new { Action = "Index", Controller = "Categories" }
        );

    //Other routes using the standard [Controller]/[Action]/[Id]

}

This will setup routes to handle category hierarchies up to 6 deep. And add Category1,Category2... into the RouteData.Values collection in the controller.

Next I set up the code to allow me to handle the route, which I did in the model, adding a method that takes an IDictionary<string,object>.

public Category GetCategoryFromRouteData(IDictionary<String,object> data)
{
    //Grab just the category data
    var navList = from route in data
               where route.Key.IndexOf("Category") == 0
               orderby route.Key
               select new{Key = route.Key, Value = route.Value.ToString()};

    string sqlSelect = @"
        SELECT {0}.* 
        FROM Category {0}
        {1}
        WHERE {0}.Name = {{0}}";
    
    //{{{2}}} will be replaced with {{<param index>}}
    string join = @"INNER JOIN Category {0} ON {0}.[Key] = {1}.ParentKey 
                    AND {0}.[Name] = {{{2}}}

    //This is the name of the category I am actually interested in
    var mainCat = navList.Last();

    //Build a list of category values to for parameterized query
    List<string> values = new List<string>();
    values.Add(mainCat.Value);
    StringBuilder sb = new StringBuilder();
    string lastCategory = mainCat.Key;

    int i = 1;
    foreach (var item in navList.Reverse().Skip(1))
    {
        sb.AppendFormat(join, item.Key, lastCategory,i++);
        values.Add(item.Value);
        lastCategory = item.Key;
    }

    string sql = String.Format(sqlSelect,mainCat.Key, sb.ToString());
    Category cat = this.ExecuteQuery<Category>(sql, values.ToArray()).Single();



    //GetDisplayCategory skips over categories that have only 1 subcategory 
    //and no examples, allowing me to have the planned Url structure without 
    //requiring the user to navigate through several empty categories.
    return GetDisplayCategory(cat);
}

I had planned on having doing it all LINQ to SQL expressions, but it was taking more time then it was worth to figure out how to do the hierarchy lookup from the category names. I need to add some caching of the key lookups at some point, since the joins look like they might get a bit nasty for deep categories, but that can wait.

I added a few overloads to the HtmlHelper ActionLink extension methods to handle making the nice Url links.

Now I need to figure out how to deploy the usercontrols that will contain the executable part of the example. I have had some problems with compilation sometimes when I had the website directly upload the usercontrols. Plus I would like them to go into source control when I add them.

Technorati Tags: aspnetmvc

Temp service provider implementation

Sean Lynch — Tue, 18 Dec 2007 23:06:34 GMT

Well, Bill Pierce in his post about making the HttpContext wrapper use the application as a service provider got me to a good enough solution for the script service I had wanted in my previous post.

While not quite as clean as adding it to the HttpContext, I think an extension method on HttpApplication like this will work well for now.

public static object GetService(this HttpApplication application,Type service)
{
    IServiceProvider provider = application as IServiceProvider;
    if (provider == null)
        return null;

    return provider.GetService(service);
}

Then add/implement the IServiceProvider on the Global class. Allowing me to get an instance of the script service using

IScriptService scriptSvc 
    = this.HttpContext.ApplicationInstance.GetService(typeof(IScriptService))
    as IScriptService;

Though though the more I think of it, the more likely I am to stick this method on the Ajax and Html helper classes. I wonder how hard it would be to add an interface like IMvcHelper to both the AjaxHelper and HtmlHelper Classes my extension method would be available to both, without duplicating code.

Technorati Tags: aspnetmvc,Service Provider,Extension Method