[c#] Database Search as you type functionality

[Linkinfamous]

Hi guys,

I have a situation where I need to be able to search a database as the user types. It's running locally in SQL Server 2005, so I've been querying every time the textbox text changes. This doesn't seem to work. Basically, if I search for '2334', '2' might have 5000 results, whereas '2334' might have 7. If I type '2334' really quickly, my current method flashes the results for '2334', then shows me the results for '2'. (D'oh!)

Basically, on text change, I prepare my query, execute it, and databind a datagridview to it. This seems to work, but not when you type quickly.

What is the proper way to do this? Then, how can I have it so that, let's say the user is typing '2334', in the text box, but by the time '2334' is in, '2' hasn't finished yet, so it can ignore the searches for '23', and '233'?

Thanks

[Bazenga]

I don't know about C#, but I can do that in Java. If C# supports mutilthreading, then it's easy "by concept".

You register a listener on that text box. When the user starts typing, you create a thread to search the database, when the user keeps typing:

1- create a thread the search the database with the user's current value entered

2 - check to see if that previous thread is still running, if so, kill it and let the current thread finish execution.

[xcguy87]

You could use the Binding Source's Filter method to do it, but then the search text would have to come from only one column.

As the user types on the textbox event, just use BindingSource1.Filter = "%COLUMNNAME% - '" + TextBox1.Text + '"

[Winston]

I remember i tried to implement this a while back, it caused the biggest issues, it's definitely not trivial, as someone mentioned you have to spawn a new thread and then check if a previous thread is running or not, and because of the nature of STA model, having to route your UI calls back on the UI thread, this causes so many issues, i mean in theory doing the thread thing actually works, but when you act like a stupid user, and type really fast and quickly backspace, it causes issues.

Many of the time filters work off index'ed files, rather than hammering the database on every new text update. The trade-off being, the results won't be up to date until it's next indexed.

I wasn't too sure about the filter's property in the binding source it always looked interesting never tried it, but, i think it's based off the premises that the data is pre-loaded into the datagrid or whatever control it maybe binded to, so the results may not be up to date one very filter call. But i suppose you can just do a re-bind on every filter call.

Also there was one thing i noticed in these filter implementations whether it be in Vista or in Spotlight, there's a delay from when a user types to when the results appear, i think it does this to prevent rapid text typing with crazy users, so maybe you can consider that as well, implementing a delay from the text-entry until the execution of the filtering method.

[Menge]

you have to do the threaded approach.

but you have to be VERY careful not to hammer your database.

for instance: you could set up a thread to do the search and only do the search every other second or so while the user is typing. that'd help you NOT kill your db when tons of users are doing the same thing. another thing you could do is index a smaller table in your database of common keywords that the user could search for and search on that (the index that Winston talked)

and about the threads, C# has a you can simply use the BeginInvoke (read the docs on these) methods to call stuff on the secondary thread as if you were on the main thread.

you have to be very careful with the threads, though :)

[Linkinfamous]

I'm not worried about hammering the database. It's not a multi-user application. It attaches the database at runtime in sql server 2005 express.

Thanks guys, hopefully I can come up with something. Any more tips, or a link to a good article, would be welcome.

Ok. Why BeginInvoke()?

I've been doing stuff like this:

void whatever()

{

if (this.invokerequired)

{

this.invoke(new whateverdelegate(whatever));

}

else

{

do whatever

}

}

Maybe i need to read up more on threading.

[Winston]

  Menge said:

and about the threads, C# has a you can simply use the BeginInvoke (read the docs on these) methods to call stuff on the secondary thread as if you were on the main thread.

you have to be very careful with the threads, though :)

Definitely. Also if you want to have it easier, in the case of doing it in .NET 2.0, you can make use of the BackgroundWorker component to help you manage calls to the UI.

[Jebadiah]

You should use a 1 second delay before the thread starts requesting data from the database. That should stop the fast typists from hammering the database each time s/he has pressed a key that edits the text.

[Linkinfamous]

Okok. Let's see if I have this right.

Every search I want to make initiates a thread. Every thread has a delay, 500ms, or 1sec or something before it does anything. After this delay, it checks to see if it's the last thread in my collection of threads. If it's not, it aborts. If it is, it ensures that there are no threads before it doing stuff. If there are, it aborts them. Then, it performs the search and updates the UI.

Good? Bad? Fundamentally flawed in every way shape and form possible, making you feel bad for my copy of visual studio?

[Linkinfamous]

Anyone see any problems with this? It seems to work....

private void doThreadWork(object dataholder)
{
	if (so == null) return;
	System.Threading.Thread.Sleep(1000);
	if (System.Threading.Thread.CurrentThread == lastThread)
	{
		for (int i = 0; i < 50; i++)
		{
			if (!aThreadIsWorking) break;
			System.Threading.Thread.Sleep(100);
		}
		try
		{
			aThreadIsWorking = true;
			//Get my list of stuff from the database and process it.
			//Send it off to a threadsafe method that sets the datagridview's DataSource
		}
		finally
		{
			aThreadIsWorking = false;
		}
	}
}

to start it all off:

System.Threading.Thread x = new Thread(new ParameterizedThreadStart(doThreadWork));
lastThread = x;
x.Start(data);