Friday, October 15, 2010

MVC 2 selct with optgroup support Html Helper

We are current building an Asp.Net MVC 2 application and we had the need for an html helper extention that renders a select with the options grouped by a field. Unfortunately there is no native helper for optgroup html tag support in Asp.Net MVC 2. I have to udmit that this is no common case either so I can not blame the guys in Microsoft for that.

The upside for this is that Asp.Net code is opensource, so I took a sneak peak in the upcomming MVC 3 source code to see what the DropDownListFor code looked like.

Lets cut to the chase.
for all kinds of select html variations MVC uses the SelectListItem class. We just need to subcass it and add a new string property named GroupKey. Here is the code fot that.

public class GroupedSelectListItem : SelectListItem
public string GroupKey { get; set; }

Then i took the helper overloads for DropDownListFor, renamed them to DropDownGroupListFor, and changed the selectlist parameter type to IEnumerable<GroupedSelectListItem>.

public static MvcHtmlString DropDownGroupListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<GroupedSelectListItem> selectList)

Finaly we just need to change a for loop inside the "GetSelectData" private method in order to take optgroup into consideration. Here is how it looks like.

foreach (var group in selectList.GroupBy(i => i.GroupKey)) {
listItemBuilder.AppendLine(string.Format("<optgroup label=\"{0}\">", group.Key));
foreach (GroupedSelectListItem item in group) {

As requested here is a usage example. Say we have the following list of vehicles in our Model.

.. and the entity class looks like this

Now in our View we add the following statement.

<%: Html.DropDownGroupListFor(model => model.VehicleId,
Lookups.Vehicles.Select(v => new GroupedSelectListItem() {
GroupKey = v.Group,
Text = v.Description,
Value = v.Id.ToString()
"---- select Vehicle ----")%>

Note that Lookups is a static helper class that gets the collection we need to bind to the dropdownlist.

public class Lookups
public static ICollection<Vehicle> Vehicles {
get {
ICollection<Vehicle> vehicles = null;
using (DBEntities context = new DBEntities()) {
vehicles = context.Vehicles.ToList();
return vehicles;

After that, we use a simple linq selection in order to transform our source collection in the form of List of GroupedSelectListItem. This is the format that the DropDownGroupListFor helper understands

If everything went according to plan then we expect to see something like this in the output:

You can download the code here (Updated: February 2011)

Friday, February 12, 2010

Filesystem out of inodes

Before version 0.9.0 redmine was storing session data in files on the tmp directory of the server. These files are usually of small size but a lot of them are produced quite fast on a production system. By default, redmine never deletes these files. A cron job could be used to delete session files older than a month or so, but to configure that cron job, you have to know of the problem first.

The easiest way to find out is to wait until you start getting “No space left on device” messages on the system log.

There are actually two reasons for such a thing to happen. The filesystem could have no more blocks available (the usual case) or the filesystem could be out of inodes (the not so usual case).

Inodes are filesystem data structures that store basic information about a regular file, directory, or other file system object. For each file, the filesystem occupies at least one inode.

The default inode ratio on an ubuntu server as configured in /etc/mke2fs.conf is one inode for every 16Kbytes of data. So creating a lot files of smaller size could lead to having enough space on the filesystem but no more inodes to create new files or directories.

You can see the amount of free inodes using df -i
Filesystem            Inodes   IUsed   IFree IUse% Mounted on
/dev/sda1            1251712 1251712       0  100% /
tmpfs                 129512       2  129510    1% /lib/init/rw
udev                  129512     488  129024    1% /dev
tmpfs                 129512       3  129509    1% /dev/shm
/dev/sda6            1251712  148360 1103352   12% /usr
/dev/sda7            35291136   21862 35269274    1% /home
/dev/sda8            35241984   31055 35210929    1% /var

Unfortunately, the system libraries of linux do not give out distinct error messages for a filesystem being out of blocks or being out of inodes. The message is always “No space left on device”.

Starting from version 0.9.0, redmine stores session data in cookies on the client side, so this problem will not occur any more.


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