Teams Winter 2011/team1/BlackBerry/Use SQLite

11. Use Database and SQLite to Store Data

11.1 Add SDCard to Simulator

To be able to have data preserved on database, first we need to make sure that simulator can simulate SDCard, so that we can run our application with database. For this purpose first create a folder on your file system. Then run the simulator and from the top menu choose: Simulate > Change SD Card... .
Then Mount Directory, and select the folder you just created. Every time you restart the simulator, before running the app you need to make sure that the folder is mounted as SD Card. later on you will see that the database file gets created there.

11.2 Create Database File

We would like to create a database file including out Student Entity, so that we can put it in the project. Then every time the app runs, first it checks if it is the first time run of the app on the device or simulator. If so, the app will copy the file in to the SDCard. Next time that you run the application, it will know that the file is there, so will not override it.

For this purpose, create a simple blackberry project with only the application object. We do not need any screen here. call it "DBCreator". and this will need to only have a class called MyApp.java which extends UIApplication. Here is the code for this class:

package mypackage;

import java.util.Enumeration;
import javax.microedition.io.file.FileSystemRegistry;
import net.rim.device.api.ui.*;
import net.rim.device.api.ui.component.*;
import net.rim.device.api.database.*;
import net.rim.device.api.io.*;

/**
 * This class extends the UiApplication class, providing a
 * graphical user interface.
 */
public class MyApp extends UiApplication
{
      private static String DB_NAME = "SQLiteStudentList";
     
    /**
     * Entry point for application
     * @param args Command line arguments (not used)
     */
    public static void main(String[] args) throws Exception
    {
        // Create a new instance of the application and make the currently
        // running thread the application's event dispatch thread.
        MyApp theApp = new MyApp();      
        theApp.enterEventDispatcher();
    }
   

    /**
     * Creates a new MyApp object
     */
    public MyApp()throws Exception
    {       
        // Check for the presence of the SDCard
          boolean sdCardPresent = false;
          String root = null;
          Enumeration e = FileSystemRegistry.listRoots();
          while (e.hasMoreElements())
          {
              root = (String)e.nextElement();
              if(root.equalsIgnoreCase("sdcard/"))
              {
                  sdCardPresent = true;
              }    
          }           
          if(!sdCardPresent)
          {
              UiApplication.getUiApplication().invokeLater(new Runnable()
              {
                  public void run()
                  {
                      Dialog.alert("This application requires an SD card to be present. Exiting application...");
                      System.exit(0);           
                  }
              });       
          }         
          else
          {
            try{
                 // create a URI object with te file name and location   
              String dbLocation = "/SDCard/databases/DBCreator/";
              URI uri = URI.create(dbLocation + DB_NAME);

                 // open a database connection to that URI
              Database db = DatabaseFactory.openOrCreate(uri, new DatabaseSecurityOptions(false));

                  // create the table if it does not already exist
              Statement statement =
                   db.createStatement("CREATE TABLE IF NOT EXISTS Student(id INTEGER PRIMARY KEY, firstName TEXT, lastName TEXT, email TEXT, address TEXT)");
                statement.prepare();
               
               //execute the statement
                statement.execute();
                
               // close statement and database
                statement.close(); 
                db.close();         
             
            }catch(Exception ex ) {
                errorDialog(ex.getMessage());
                System.exit(0);   
          }
           
          }
    }
   
   // Error message dialog
    public static void errorDialog(final String message)
    {
        UiApplication.getUiApplication().invokeLater(new Runnable()
        {
            public void run()
            {
                Dialog.alert(message);
            }
        });
    }
}

Now run tha application. Then from the SDCard folder, drag the database file and drop it into your main project, "res" folder.

11.3 Add id to Student Class

Now in our main application project,we need to add id to this class because we are going to preserve our Student objects in database,: So add a private field and add public getter and setters:

public int getId(){
        return this.id;
        }
    public void setId(int id){
        this.id = id;
    }

11.4 Check for presence of SDCard

Each time our "Student View" application runs, we have to check for the presence of the SD card, and if it does not exist, we have to show a dialog message.

Therefore, add the following code to the ViewStudentApp.java class constructor:

public ViewStudentApp() throws Exception {
        //This part is from BB Sample application
         // Determine if an SDCard is present
        boolean sdCardPresent = false;
        String root = null;
        Enumeration e = FileSystemRegistry.listRoots();
        while (e.hasMoreElements())
        {
            root = (String)e.nextElement();
            if(root.equalsIgnoreCase("sdcard/"))
            {
                sdCardPresent = true;
            }    
        }  
       
        if(!sdCardPresent)
        {
             UiApplication.getUiApplication().invokeLater(new Runnable()
             {
                 public void run()
                 {
                     Dialog.alert("This application requires an SD card to be present. Exiting application...");
                     System.exit(0);           
                 }
             });  
        }         
        else
        {
            // the rest of code goes here

        }

11.5 Copy Database File into SDCard

Now that application knows SDCard is present, It should check if the database file exist, otherwise copy it from the application bundle into SDCard:

  else
        {
            String dbLocation = "/SDCard/databases/StudentsList/";
           
            // Create URI           
            uri = URI.create(dbLocation + DB_NAME);    
           
            // Open or create a plain text database.  This will create the
            // directory and file defined by the URI (if they do not already exist).
           db = DatabaseFactory.openOrCreate(uri, new DatabaseSecurityOptions(false)); 
           
            // Close the database in case it is blank and we need to write to the file
            db.close();
           
            // Open a connection to the database file       
            FileConnection fileConnection = (FileConnection)Connector.open("file://" + dbLocation + DB_NAME);   
           
            // If the file is blank, copy the pre-defined database from this
            // module to the SDCard.
            if(fileConnection.exists() && fileConnection.fileSize() == 0)
            {                     
                readAndWriteDatabaseFile(fileConnection);          
            }        
        // here goes the rest of the constructor code
          _studentList = new StudentList(db, uri);

Then add the following method (readAndWriteDatabaseFile) to the file that actually reads the database file and puts it into the simulator: <sourse lang="java">

public void readAndWriteDatabaseFile(FileConnection fileConnection) throws IOException
       {       
           OutputStream outputStream = null;
           InputStream inputStream = null;      
                         
           // Open an input stream to the pre-defined encrypted database bundled
           // within this module.
           inputStream = getClass().getResourceAsStream("/" + DB_NAME);
          
           // Open an output stream to the newly created file
           outputStream = (OutputStream)fileConnection.openOutputStream();                                      
          
           // Read data from the input stream and write the data to the
           // output stream.           
           byte[] data = new byte[256];
           int length = 0;
           while (-1 != (length = inputStream.read(data)))
           {
               outputStream.write(data, 0, length);               
           }    
          
           // Close the connections
           if(fileConnection != null)
           {
               fileConnection.close();
           }
           if(outputStream != null)
           {
               outputStream.close();
           }
           if(inputStream != null)
           {
               inputStream.close();
           }           
       }
      

</source>

11.6 Create SQLiteManager Class

Now we need a class that will be the only class interacting with our database. It will take a Database object and a URI object to open database in the constructor. It will have methods to perform all the queries we need and at the end of each query will close the database.

So, create a class called: SQLiteManager 11.6.1 Open Database
11.6.2 Close Database
11.6.3 Select All Students
11.6.4 Insert New Student
11.6.5 Delete Student
11.6.6 Update Student

11.7 Modify StudentsList Class to use SQLiteManager

11.7.1 Load list
11.7.2 Add Student
11.7.3 Edit Student
11.7.4 Delete Student