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→11.2 Create Database File
===11.2 Create Database File===
We would like to create a database file including out our 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. <Br/>
For this purpose, create a simple blackberry project with only the application object. We do not need any screen here. call it "DBCreator".
public MyApp()throws Exception
{
// Push a screen onto Check for the UI stack for rendering.presence of the SDCard
boolean sdCardPresent = false;
String root = null;
// 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();
}
</source>
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:
<source lang="java">
public int getId(){
return this.id;
}
public void setId(int id){
this.id = id;
}
</source>
===11.3 Add id 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 Student the ClassViewStudentApp.java class constructor:<source lang="java"> 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:
<source lang="java">
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);
}
// notice that the way we are callling the StudentList constructor is now different.
// Later on you will see that we should modify that class:
_studentList = new StudentList(db, uri);
// here goes the rest of the constructor code
</source>
Then add the following method (readAndWriteDatabaseFile) to the file that actually reads the database file and puts it into the simulator:
<source 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. <br/> So, create a class called: SQLiteManager, with 2 private fields, and a constructor that sets them and then tries to open database:<source lang="java"> package cs.ecl.team1.project; import java.util.Vector;import net.rim.device.api.database.Cursor;import net.rim.device.api.database.DataTypeException;import net.rim.device.api.database.Database;import net.rim.device.api.database.DatabaseException;import net.rim.device.api.database.DatabaseFactory;import net.rim.device.api.database.Row;import net.rim.device.api.database.Statement;import net.rim.device.api.io.URI;import net.rim.device.api.ui.UiApplication;import net.rim.device.api.ui.component.Dialog; public class SQLManager { private static Database db; private URI uri; public SQLManager(Database db, URI uri) { this.uri = uri; this.db = db; openDB(); } }</source>'''11.6.1 Open Database'''<br/>Then we implement the openDB() method:<source lang="java"> void openDB() { try { this.db = DatabaseFactory.open(uri); } catch(DatabaseException dbe) { errorDialog(dbe.toString()); } } </source>'''11.6.2 Close Database'''<br/>Then we definitely need a closeDB() method to use later:<source lang="java"> static void closeDB() { try { db.close(); } catch(DatabaseException dbe) { errorDialog(dbe.toString()); } } </source>And as you noticed above, we are going to need a method called errorDialog():<source lang="java"> public static void errorDialog(final String message) { UiApplication.getUiApplication().invokeLater(new Runnable() { public void run() { Dialog.alert(message); } }); }</source>'''11.6.3 Select All StudentsInsert New Student'''<br/>The first query we need is a query that enables us add a new Student, so we need to implement a method for that:<source lang="java"> //ADD STUDENT Student addStudent(String fName, String lName, String email, String address){ Student student = null; try { Statement statement = db.createStatement("INSERT INTO Student VALUES(NULL,?,?,?,?)"); statement.prepare(); statement.bind(1,fName); statement.bind(2, lName); statement.bind(3, email); statement.bind(4, address); statement.execute(); statement.close(); statement = db.createStatement("SELECT id FROM Student WHERE firstName = ? AND lastName = ?"); statement.prepare(); statement.bind(1, fName); statement.bind(2, lName); Cursor cursor = statement.getCursor(); if(cursor.next()) { Row row = cursor.getRow(); int id = row.getInteger(0); student = new Student(id, fName, lName, email, address); } cursor.close(); statement.close(); }catch(DatabaseException dbe) { errorDialog(dbe.toString()); } catch(DataTypeException dte) { errorDialog(dte.toString()); } return student; }</source> '''11.6.4 Insert New Delete Student'''<br/>Then add a method to delete student by id: <source lang="java"> // DELETE STUDENT void deleteStudent(int id) { try { Statement statement = db.createStatement("DELETE FROM Student WHERE id = ?"); statement.prepare(); statement.bind(1, id); statement.execute(); statement.close(); } catch(DatabaseException dbe) { errorDialog(dbe.toString()); } } </source>'''11.6.5 Delete Update Student'''<br/>And a method to update Student:<source lang="java"> //UPDATE STUDENT void updateStudent(int id, String fName, String lName, String email, String address) { try { Statement statement = db.createStatement("UPDATE Student SET firstName = ?, lastName= ?, email = ?, address = ? WHERE id = ?"); statement.prepare(); statement.bind(1, fName); statement.bind(2, lName); statement.bind(3, email); statement.bind(4, address); statement.bind(5, id); statement.execute(); statement.close(); } catch(DatabaseException dbe) { errorDialog(dbe.toString()); } } </source> '''11.6.6 Update Select All Students'''<br/>And obviously we will need a method that gets all the students from database and returns a vector of Student, so that we can populate our student list:<source lang="java"> Vector getStudents(){ Vector students= new Vector(); try { Statement statement = db.createStatement("SELECT * FROM Student"); statement.prepare(); Cursor cursor = statement.getCursor(); // Iterate through the the result set. For each row, add a // new DirectoryItem object to the vector. while(cursor.next()) { Row row = cursor.getRow(); int id = row.getInteger(0); String fName = row.getString(1); String lName = row.getString(2); String email = row.getString(3); String address = row.getString(4); Student student = new Student(id, fName, lName, email, address); students.addElement(student); } statement.close(); cursor.close(); } catch(DatabaseException dbe) { errorDialog(dbe.toString()); } catch(DataTypeException dte) { errorDialog(dte.toString()); } return students; }<br/source>
===11.7 Modify StudentsList Class to use SQLiteManager===
So far the StudentList class we have, consumes a vector to store students whiche are note preserved. We will modify the methods of this list to use the SQLiteManager and preserve the objects.<br/>Add the following private fields to the StudentList Class:<source lang="java"> private Database db ; private URI uri;</source>Then modify its constructor to take and set thode fields:<source lang="java">public StudentList(Database db, URI uri) throws Exception { super(new StudentListComparator()); this.db = db; this.uri = uri; SQLManager sqlManager = new SQLManager(db, uri); loadFrom(sqlManager.getStudents().elements()); SQLManager.closeDB(); } </source> '''11.7.1 Load list'''<br/>As noticed above, the constructor then passes those objects to a new SQLiteManager object and gets students from the manager to load the list with. Then it closes the database.<br/> '''11.7.2 Add Student'''<br/>Now modify the addElement method:<source lang="java">/** * Adds a new element to the list. * @param element The element to be added. */ void addElement(Object element) { Student student = (Student) element; SQLManager sqlManager = new SQLManager(db, uri); sqlManager.addStudent(student.getFirstname(), student.getLastName(), student.getEmail(), student.getAddress()); doAdd(element); SQLManager.closeDB(); } </source>'''11.7.3 Edit Student'''<br/>And editElement method:<source lang="java">// added for Update: void updateElement(Object oldElement, Object newElement){ Student student = (Student) newElement; SQLManager sqlManager = new SQLManager(db, uri); sqlManager.updateStudent(student.getId(), student.getFirstname(), student.getLastName(), student.getEmail(), student.getAddress()); doUpdate(oldElement,newElement); SQLManager.closeDB(); } </source>'''11.7.4 Delete Student'''<br/><source lang="java">/** * Removes element from the list * @param element */ void deleteElement(Object element) { Student student = (Student)element; SQLManager sqlManager = new SQLManager(db, uri); sqlManager.deleteStudent(student.getId()); doRemove(element); SQLManager.closeDB(); } </source>
===11.8 Run Student View Application in Action===Now if you run the application, you will get the same functionality as before, but this time data is saved. Don't forget to add SDCard to simulator before running it.
