Persistent store handling

Question

Hi, I am working on email kind of application on Blackberry. I want to store all the mails in persistent store. Also the list of contacts needs to be stored.

How do I manipulate such kind of functionality using persistet store?

How do I store data?

Can multiple messages are saved ?

And how to acccess them correctly and display on screen?

I have never worked on persistent store before, please help.

Answer 1

There is no indexing in persistent storage.
You can save and retrieve arrays of Persistable objects.
On example, Contact Persistable:

public class Contact implements Persistable{
    int mId; String mAdress; String mName;    
    public Contact( int id, String adress, String name ){
        mId = id; mAdress = adress; mName = name;
    }    
}

Mail Persistable:

public class Mail implements Persistable{
    String mMessage = null; int mSenderId = -1; int[] mReceiverIdList = null;    
    public Mail(String message, int senderId, int[] receiverIdList){
        mMessage = message; mSenderId = senderId; 
        mReceiverIdList = receiverIdList;
    }
}

Some Helper class:

public class PersistentStoreHelper{
    static PersistentObject contactStore = PersistentStore
            .getPersistentObject( 0xf140775afcb94f90L );
    static PersistentObject mailStore = PersistentStore
    .getPersistentObject( 0xd43b0423228ff7c0L );
    public static void saveContacts( Contact[] contacts ){
        saveObject( contactStore, contacts );
    }
    public static void saveMails( Mail[] mails ){
        saveObject( mailStore, mails );
    }
    public static Contact[] retrieveContacts(){
        return ( Contact[] )retrieveObject( contactStore );
    }
    public static Mail[] retrieveMails(){
        return ( Mail[] )retrieveObject( mailStore );
    }
    public static void saveObject( PersistentObject store, Object object ){
        synchronized( store ){
            store.setContents( object );
            store.commit();
        }
    }
    public static Object retrieveObject( PersistentObject store ){
        Object result = null;
        synchronized( store ){
            result = store.getContents();
        }
        return result;
    }
}

And sample of using:

class Scr extends MainScreen implements FieldChangeListener{
    ButtonField mBtnInit = null;
    BasicEditField mInputSenderId = null;
    BasicEditField mInputReceiverId = null;
    ButtonField mBtnSearch = null;
    VerticalFieldManager mMailsList = null;
    public Scr(){
        mBtnInit = new ButtonField( "Init Persistenet Storage", 
            ButtonField.CONSUME_CLICK );
        mBtnInit.setChangeListener( this );
        add( mBtnInit );
        mInputSenderId = new BasicEditField( "sender id:", "43" );
        add( mInputSenderId );
        mInputReceiverId = new BasicEditField( "receiver id:", "12" );
        add( mInputReceiverId );
        mBtnSearch = new ButtonField( "Search", ButtonField.CONSUME_CLICK );
        mBtnSearch.setChangeListener( this );
        add( mBtnSearch );
        mMailsList = new VerticalFieldManager();
        add( mMailsList );
    }
    public Vector getMailByIds( int senderId, int recepientId ){
        Vector result = new Vector();
        Mail[] mails = PersistentStoreHelper.retrieveMails();
        for( int i = 0; i < mails.length; i++ )
            if( mails[ i ].mSenderId == senderId ){
                int[] receiverIdList = mails[ i ].mReceiverIdList;
                for( int j = 0; j < receiverIdList.length; j++ )
                    if( recepientId == receiverIdList[ j ] )
                        result.addElement( mails[ i ] );
            }
        return result;
    }
    public void initPersistentStorage(){
        // create 100 contacts and save them
        Contact[] contacts = new Contact[ 100 ];
        for( int i = 0; i < 100; i++ ){
            String name = "name" + String.valueOf( i );
            String adress = name + "@mail.com";
            contacts[ i ] = new Contact( i, adress, name );
        }
        PersistentStoreHelper.saveContacts( contacts );
        // create messages from each to every contact and save them
        Mail[] mails = new Mail[ 10000 - 100 ];
        int k = 0;
        for( int i = 0; i < 100; i++ )
            for( int j = 0; j < 100; j++ )
                if( i != j ){
                    Mail mail = new Mail( "Hello!", contacts[ i ].mId, 
                        new int[]{ contacts[ j ].mId } );
                    mails[ k ] = mail;
                    k++;
                }
        PersistentStoreHelper.saveMails( mails );        
    }
    public void fieldChanged( Field field, int context ){
        if( field == mBtnInit )
            initPersistentStorage();
        else if( field == mBtnSearch ){
            mMailsList.deleteAll();
            int senderId = Integer.parseInt( mInputSenderId.getText() );
            int receiverId = Integer.parseInt( mInputReceiverId.getText() );
            Contact[] contacts = PersistentStoreHelper.retrieveContacts();
            Vector result = getMailByIds( senderId, receiverId );
            for( int i = 0, cnt = result.size(); i < cnt; i++ )
            {
                Mail mail = ( Mail )result.elementAt( i );
                String from = "From: " + contacts[ mail.mSenderId ].mName 
                        + " <" + contacts[ mail.mSenderId ].mAdress + ">";
                String to = "To: ";
                for( int j = 0; j < mail.mReceiverIdList.length; j++ )
                {
                    int id = mail.mReceiverIdList[ j ];
                    to += contacts[ id ].mName + " <" 
                        + contacts[ id ].mAdress + ">; ";
                }
                to = to.substring( 0, to.length() - 2 );
                String msg = "Message: " + mail.mMessage;
                mMailsList.add( new LabelField( from ) );
                mMailsList.add( new LabelField( to ) );
                mMailsList.add( new LabelField( msg ) );
            }
        }
    }
}

Read BlackBerry Java Application - Core - Development Guide - Persistent Storage
Also you can read riccomini - code blackberry persistent store