Eclipsed4utoo's Blog

Using SqlDependency To Monitor SQL Database Changes

Ryan Alford — Tue, 23 Feb 2010 22:00:34 +0000

The purpose of this class is to save you from having to continuously re-query the database to get new data. You would have probably done this by setting up a timer that executes every X amount of seconds so that your display control would be displaying the most up-to-date information. You will no longer have to do this.

We will be using a Service Broker and a QUEUE in SQL Server 2005. These were new additions to SQL Server 2005. I will assume these are also in SQL Server 2008, but can’t guarantee.

My example will be doing something very simple. I have a “Users” table in my database with two fields: FirstName and LastName. I am simply displaying these in a ListBox on one form. On a second form, I have textboxes to insert the data into the database.

So first, we need to create the Queue and the Service broker and assign the privileges to the SQL user.

USING [YourDatabaseName]

CREATE QUEUE NameChangeQueue;
CREATE SERVICE NameChangeService ON QUEUE NameChangeQueue
([http://schemas.microsoft.com/sql/notifications/postquerynotification]);

GRANT SUBSCRIBE QUERY NOTIFICATIONS TO YourUserName;

You can now see that we have a new queue and a new service.

Now we move on to the code. The first thing you will need to do is to test if the connecting user has the privileges for the query notifications.

private bool DoesUserHavePermission()
{
     try
     {
           SqlClientPermission clientPermission = new SqlClientPermission(PermissionState.Unrestricted);

           // will throw an error if user does not have permissions
           clientPermission.Demand();

           return true;
     }
     catch
     {
           return false;
     }
}

Next, we have our method to get the user names from the database.

private void GetNames()
{
    if (!DoesUserHavePermission())
        return;

    lbNames.Items.Clear();

    SqlDependency.Stop(connectionString);
    SqlDependency.Start(connectionString);

    using (SqlConnection cn = new SqlConnection(connectionString))
    {
        using (SqlCommand cmd = cn.CreateCommand())
        {
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "SELECT FirstName, LastName FROM dbo.[Users]";

            cmd.Notification = null;

            SqlDependency dep = new SqlDependency(cmd);
            dep.OnChange += new OnChangeEventHandler(dep_OnChange);

            cn.Open();

            using (SqlDataReader dr = cmd.ExecuteReader())
            {
                while (dr.Read())
                {
                    lbNames.Items.Add(dr.GetString(0) + " " + dr.GetString(1));
                }
            }
        }
    }
}

THIS IS VERY IMPORTANT.

1. In the previous code, you will notice that my SQL query does not use the “*” wildcard to return all columns. You MUST return the exact columns that you want. If you use the “*”, it will cause you to have unwanted consequences.

2. Also in the previous code, you will notice that my SQL query contains the “two-part” table name. This is also REQUIRED. Using just “TableName” instead of “owner.TableName” will also cause unwanted consequences.

Here is the method for the OnChange event

void dep_OnChange(object sender, SqlNotificationEventArgs e)
{
    // this event is run asynchronously so you will need to invoke to run on UI thread.
    if (this.InvokeRequired)
        lbNames.BeginInvoke(new MethodInvoker(GetNames));
    else
        GetNames();

    // this will remove the event handler since the dependency is only for a single notification
    SqlDependency dep = sender as SqlDependency;
    dep.OnChange -= new OnChangeEventHandler(dep_OnChange);
}

You will also need to stop the dependency when the form closes so that it doesn’t leave it running.

private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
    SqlDependency.Stop(connectionString);
}

The other events…

private void Form1_Load(object sender, EventArgs e)
{
    GetNames();
}

private void btnShowForm_Click(object sender, EventArgs e)
{
    Form2 f = new Form2();
    f.Show();
}

And my simple second form’s code..

private void btnSave_Click(object sender, EventArgs e)
{
    using (SqlConnection cn = new SqlConnection("Data Source=alfordr;Initial Catalog=MyTestDatabase;User Id=dev;Password=dev;"))
    {
        using (SqlCommand cmd = cn.CreateCommand())
        {
            cmd.CommandText = "INSERT INTO Users VALUES (@FirstName, @LastName)";
            cmd.CommandType = CommandType.Text;

            cmd.Parameters.AddWithValue("@FirstName", txtFirstName.Text);
            cmd.Parameters.AddWithValue("@LastName", txtLastName.Text);

            cn.Open();

            cmd.ExecuteNonQuery();
        }
    }
}

And that is really all you have to do. Here are a couple of screenshots.

Before clicking “Save”…

After clicking “Save”…..

As you can see from my code, I am simply inserting data into my database when the Save button is clicked. When the data is inserted, a notification is sent to the application, which is handled by the OnChange event. The OnChange event then invokes the GetNames method which re-queries the database to get the new information. This makes a huge performance improvement because I ONLY query when I need to.

This works for inserts, updates, and deletes.

In this tutorial, I will use the SqlDependency class and Query notifications to monitor SQL Server 2005 database data changes. Query Notifications allow an application to be notified when data has changed in the database.

The purpose of this class is to save you from having to continuously re-query the database to get new data. You would have probably done this by setting up a timer that executes every X amount of seconds so that your display control would be displaying the most up-to-date information. You will no longer have to do this.

We will be using a Service Broker and a QUEUE in SQL Server 2005. These were new additions to SQL Server 2005. I will assume these are also in SQL Server 2008, but can’t guarantee.

My example will be doing something very simple. I have a “Users” table in my database with two fields: FirstName and LastName. I am simply displaying these in a ListBox on one form. On a second form, I have textboxes to insert the data into the database.

So first, we need to create the Queue and the Service broker and assign the privileges to the SQL user.In this tutorial, I will use the SqlDependency class and Query notifications to monitor SQL Server 2005 database data changes. Query Notifications allow an application to be notified when data has changed in the database.

The purpose of this class is to save you from having to continuously re-query the database to get new data. You would have probably done this by setting up a timer that executes every X amount of seconds so that your display control would be displaying the most up-to-date information. You will no longer have to do this.

We will be using a Service Broker and a QUEUE in SQL Server 2005. These were new additions to SQL Server 2005. I will assume these are also in SQL Server 2008, but can’t guarantee.

My example will be doing something very simple. I have a “Users” table in my database with two fields: FirstName and LastName. I am simply displaying these in a ListBox on one form. On a second form, I have textboxes to insert the data into the database.

So first, we need to create the Queue and the Service broker and assign the privileges to the SQL user.

WPF – Using an Application Configuration File

Ryan Alford — Fri, 05 Feb 2010 19:16:01 +0000

This is going to be a real short post about an issue that I ran into recently with WPF.

I was wanting to use an app config file with my WPF application. I was running into an issue with the ConfigurationManager calls not getting the information from the app config file.

I added the app config just like I would in a Windows Form..

My app config file looked something like this…

I was using the standard code that works fine in Windows Forms(needed to add a reference to the System.Configuration):

using System.Configuration

private void Window_Loaded(object sender, RoutedEventArgs e)
{
     var myKey = ConfigurationManager.AppSettings["myKey"];
}

However, the app settings were not being found. After scratching my head for a while and searching numerous places online, I found a small response on a forum. None of the “MVP”s picked up on it. It was because of the name of the app config file. By default, VS2008 added the file as “App1.config”. For some reason, the ConfigurationManager class looks for a file named exactly “App.config”.

So simply changing the name of the config file to “App.config” fixed the issue and the code started working.

C# – Log in to Website Programmatically

Ryan Alford — Fri, 22 Jan 2010 22:00:41 +0000

In this tutorial, will show how to log into a website through code. I am going to use Twitter in my example.

THIS IS FOR EDUCATIONAL PURPOSES ONLY. I WOULD NOT ADVISE THE USE OF THIS TO ALWAYS LOG-IN TO TWITTER.

First, you will need to download and install Tamper Data. It’s an add-on for Firefox that allows you to view and tamper with GET/POST web request data. We won’t be doing any tampering. We will be using it to view what POST parameters the page is expecting.

Next, navigate to the log in page for Twitter(http://twitter.com/login). Once the page has loaded, go to Tools –> Tamper Data to open Tamper Data. At the top of Tamper Data, click the Start Tamper button. After clicking the button, click the “Sign In” button on Twitter’s log in page. Once you hit the Sign In button, Tamper Data will prompt you with this popup….

Click “Tamper”. You will then be presented with this window…

If you notice on the right-hand side of the window, you will see the POST parameters. These are:

authenticity_token
session[username_or_email]
session[password]
commit

Now that we have those, we can close the Tamper Data window, and close Firefox.

Now for the code. The code is actually fairly simple. We are just going to use the WebBrowser class to make the requests to the server to get the html source of the page. This will give us the “authenticity_token” for us to use in the POST request.

string url = "https://twitter.com/login";
string username = "someUserName";
string password = "somePassword";
string commit = "Sign+In"; //this matches the data from Tamper Data

private void Login()
{
     WebBrowser b = new WebBrowser();
     b.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(b_DocumentCompleted);
     b.Navigate(url);
}

private void b_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
     WebBrowser b = sender as WebBrowser;
     string response = b.DocumentText;

     // looks in the page source to find the authenticity token.
     // could also use regular expressions here.
     int index = response.IndexOf("authenticity_token");
     int startIndex = index + 41;
     string authenticityToken = response.Substring(startIndex, 40);

     // unregisters the first event handler
     // adds a second event handler
     b.DocumentCompleted -= new WebBrowserDocumentCompletedEventHandler(b_DocumentCompleted);
     b.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(b_DocumentCompleted2);

     // format our data that we are going to post to the server
     // this will include our post parameters.  They do not need to be in a specific
     //    order, as long as they are concatenated together using an ampersand ( & )
     string postData = string.Format("authenticity_token={2}&session[username_or_email]={0}&session[password]={1}&commit={3}", username, password, authenticityToken, commit);

     ASCIIEncoding enc = new ASCIIEncoding();

     //  we are encoding the postData to a byte array
     b.Navigate("https://twitter.com/sessions", "", enc.GetBytes(postData), "Content-Type: application/x-www-form-urlencoded\r\n");
}

private void b_DocumentCompleted2(object sender, WebBrowserDocumentCompletedEventArgs e)
{
     WebBrowser b = sender as WebBrowser;
     string response = b.DocumentText;

     if (response.Contains("Sign out"))
     {
         MessageBox.Show("Login Successful");
     }
}

And that’s all you need to do. You can now use the response variable to see the tweets that are in your timeline.

Android – Open Contacts Activity and Return Chosen Contact

Ryan Alford — Wed, 30 Dec 2009 18:12:26 +0000

I was looking for a way to open the Contacts Activity, chose a Contact, then have that Contact returned to my application. I found a number of code snippets, but they all used depreciated API calls. So I decided to make this post with the updated API calls for Android 2.0.

First, you will need to add this permission to your AndroidManifest.xml file:

Next, add this constant as a class level variable:

private static final int PICK_CONTACT = 3;

Now, you will add the code to open the Contacts Activity. This is done by using an Intent:

// I did this from a button click
public void btnAddContacts_Click(View view){
     Intent intent = new Intent(Intent.ACTION_PICK, ContactsContract.Contacts.CONTENT_URI);
     startActivityForResult(intent, PICK_CONTACT);
}

Now, you will override the “onActivityResult” activity method, and get the Contact information:

@Override
public void onActivityResult(int reqCode, int resultCode, Intent data){
    super.onActivityResult(reqCode, resultCode, data);

    switch(reqCode){
       case (PICK_CONTACT):
         if (resultCode == Activity.RESULT_OK){
             Uri contactData = data.getData();
             Cursor c = managedQuery(contactData, null, null, null, null);

             if (c.moveToFirst()){
                 // other data is available for the Contact.  I have decided
                 //    to only get the name of the Contact.
                 String name = c.getString(c.getColumnIndexOrThrow(ContactsContract.Contacts.DISPLAY_NAME));
                 Toast.makeText(getApplicationContext(), name, Toast.LENGTH_SHORT).show();
             }
         }
    }
}

And that is all you need to do.

ASP.Net – AJAX and an External Javascript File

Ryan Alford — Tue, 22 Dec 2009 22:00:44 +0000

Recently, I needed to add a color picker to a web application. I thought I would try the new AJAX toolkit, but the toolkit was full of issues so I had to resort to doing it with javascript. I downloaded a color picker that somebody had done(and donated for their development).

When I went to add the external javascript file and the other associated files, my AJAX page would no longer show up. Anything inside of an UpdatePanel would not show up. I did some searching and found that using an external javascript file can cause AJAX to fail.

I originally had this code which was giving me issues.


    
    ");
}

And that would work…for the most part. Only in IE, you would be given this message..

Now, if you wanted to get around that message, you could need to do this:

// This code works in IE 7, Firefox 3.5, and Chrome 3.0
protected void btnClose_Click(object sender, EventArgs e)
{
     Response.Write("");
}

This will no longer show the message and just close the window.

Uncharted 2 Causing PS3 to Freeze

Ryan Alford — Thu, 22 Oct 2009 16:43:05 +0000

I recently bought Uncharted 2. While the game is amazing, during the first 2 hours or so of gameplay, my PS3 froze 5 times. I was thoroughly pissed off about it since I had just bought the game.

After the 5th freeze, I decided to check the system updates for the PS3. I was running version 3.0. Sony released 3.01 on September 15th, but it was only an optional update which means you aren’t required to install it to still be able to access the PSN.

After updating to 3.01, I have played about 6 more hours and have not had another problem. The change log for 3.01 is “System stability during use of some PlayStation®3 format software has been improved.”. I can only assume that Uncharted 2 is one of those titles that was improved.

So for anybody who may be having problems with freezing while playing Uncharted 2, downloading the 3.01 update may help.