Autocomplete functionality using prefix trees

Update: all the source code for this article can be accessed from here

This is a follow up to my previous post on implementing a prefix tree in C#.

This expands on that idea and uses the data structure to generate a list of autocomplete matches for a given input character sequence.

These are the modifications I brought to the code:





This is the main program:

Implementation of the prefix tree(trie) data structure in C#

Update: all the source code for this article can be accessed from here

A prefix tree is a data structure with many uses. I won't go into details about this data structure Wikipedia does a better job than I could. What I will do is post a C# implementation of this data structure and in a following post I will show how to use this data structure when implementing an auto-complete solution.

These are the properties of a prefix tree:

• it stores strings(finite sequences of chars)
• it had nodes :) (doooooooh!)
• each node stores a character
• each node can have a number of subnodes(0,1,2, ... infinity)
• the char stored in a subnode is the one following the char stored by the node in a string
• each node has a flag which is raised if a word ends there(this doesn't mean it can't have subnodes for example a prefix tree can store the words "cat" and "catastrophy" in this case node 3 stores 't' and has a subnode that stores 'a')

And now the code:

The node:



The tree:

The main program:

How to concatenate data from multiple rows into a single rows

I had a problem once. One table had a lot of data in a column on multiple rows. I had to display it in a view but I needed all the data on that column to be displayed in a single cell on a row. This view was supposed to be the data source for a report ... long story ...

Anyway, the basic idea is this:

SELECT some_column = (your select query
 for xml path(''))

this only works in sql server 2008 because earlier versions don't have the "xml" keyword.

Here is an example:

SELECT Documente = (SELECT coalesce(td.Descriere+',','') as [text()] FROM Document d 
   INNER JOIN TipDocument td ON d.TipDocumentId = td.Id  for xml path(''))

Unable to start debugging on the web server error

Just in case you also received this error:

Unable to start debugging on the web server. Debugging failed because
integrated Windows authentication is not enabled. Please see Help for
assistance

Here is what I did to not get it any more

1. Open IIS Manager (Internbet Information Services)
2. Right-click the web site (in case you run it locally you only have
   Default web site) and pick Properties
3. Choose "Directory Security" tab and click Edit on "Anonymous access and
   authentication control"
4. In the opening window, uncheck "Allow Anonymous access" and check
   "Integrated Windows Authentication"

Finding the path to an installed application in C#

Well, you can find the path to a locally installed application by querying the windows registry.

The information is here:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\

Example photoshop.exe

I wrote this function in C# to do this for me:

/// 

        /// get the path to a specific application from the registry 
        /// 
        /// name of the application exe
        /// 
        public static string GetApplicationPath(string ExeName)
        {
            try
            {
                RegistryKey OurKey = Registry.LocalMachine;
                OurKey = OurKey.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\App Paths\"+ExeName, true);
                if (OurKey != null)
                    return OurKey.GetValue("").ToString();
                else
                    return "";
            }
            catch(Exception ex)
            {
                return "";
            }
        }

Exporting MS SQL data as sql scripts

In PhpMyAdmin exporting data to sql statements not to .mdb files or other databases is very straight forward. When I first had to do this with Sql Management Studio I didn't know how at first.

Then I found out.

Basically, what you have to do is this:

1.right click on a database item

2.go to tasks -> generate scripts in the menu that appears

You now have a wizard that will help you generate scripts for the objects you need. You can either generate one script for all the objects in your database(tables, triggers, stored procedures etc) or one script for just some of the object(you choose which) or each object you choose in it's own script. You can either generate these resulting scripts in files or in new query windows. Everything is configurable from the options window(the wizard step with the title "Choose script options").

Here is an example:

I wanted to just script the triggers in a db. Each in it's own file.

In the options window I set "script triggers" to true and in the following wizard form(with the title "Output options") I chose "file per object".

Reseting visual studio

Visual Studio needs to be reset(in order to change a setting) / is frozen / doesn’t work right

1. Close all instances of VS

2. Click Start > Run...

3. Type "devenv /resetuserdata"

4. Open task manager and wait until devenv.exe process is finished executing

5. Restart VS2005

In Win 7:

search for the folder in which devenv.exe can be found

follow the steps above but instead of typing “devenv /resetuserdata” type “devenv.exe /resetuserdata”