GWT Mobile Persistence

gwtmobile-persistence is a GWT wrapper of the Javascript object-relational mapper library persistence.js. It provides client-side object persistence capability to GWT applications, a feature similar to what Hibernate provides for GWT applications on the server-side.

gwtmobile-persistence is part of GWT Mobile, a GWT mobile development platform.

Schema definition

The schema is defined by declaring an interface for each entity. The interface needs to extend the Persistable marker interface.

public interface Category extends Persistable {
	public String getName();				// Property
	public void setName(String name);
	public Collection<Task> getTasks();		// One to many relationship
}

Each getter method defines a property on the entity. Setter method is optional. If a getter method returns a Collection<T extends Persistable> type, that getter method defines a "one to many" or "many to many" relationship. The actual relationship type is determined by the definition on the other entity, Task in the example.

public interface Task extends Persistable {
	public String getName();
	public void setName(String name);
	public String getDescription();
	public void setDescription(String description);
	public boolean getDone();	
	public void setDone(boolean done);
	public Category getCategory();				//many to one relationship
	public void setCategory(Category category);
	public Collection<Tag> getTags();			//many to many relationship	
}

If the return type of a getter method extends the Persistable marker interface, then the getter method defines an inverse "one to many" relationship.

public interface Tag extends Persistable {
	public String getName();
	public void setName(String name);	
	public Collection<Task> getTasks();			// Many to many relationship
}

If the getter methods on both ends of the relationship return a Collection<T extends Persistable>, that is a "many to many" relationship.

Object creation and persistence

The entity is created with the GWT.create call. For example, GWT.create(Task.class) creates an entity of Task. The type of the created entity is Entity<Task>. To create an object of the entity, use the Entity<T>.newInstance method. The return type of the newInstance method is T. For example, Entity<Category>.newInstance returns an object of type Category.

final Entity<Task> taskEntity = GWT.create(Task.class);
final Entity<Tag> tagEntity = GWT.create(Tag.class);
final Entity<Category> categoryEntity = GWT.create(Category.class);

Persistence.connect("YourDBName", "Your DB Description", 5 * 1024 * 1024);
Persistence.setAutoAdd(true);	//This is optional. When set, object created by Entity.newInstance() will
								//be added to persistence automatically.

Persistence.schemaSync(new Callback() {
	public void onSuccess() {
		final Category c = categoryEntity.newInstance();
		c.setName("Main");
		final Tag tag = tagEntity.newInstance();
		tag.setName("Urgent");
		for (int i = 0; i < 5; i++) {
			Task t = taskEntity.newInstance();
			t.setName("Task" + Integer.toString(i));
			t.setDescription("Task No #" + Integer.toString(i));
			t.setDone(i % 2 == 0);
			t.setCategory(c);
			t.getTags().add(tag);
		}
	
		Persistence.flush(new Callback() {
			public void onSuccess() {
				Collection<Task> allTasks = c.getTasks().filter("Done", "==", true);
				allTasks.list(new CollectionCallback<Task>() {
					public void onSuccess(Task[] results) {
						for (Task task : results) {
							RootPanel.get("taskNameContainer").add(new Label(task.getName()));
						}
					}
				});					
				Persistence.reset();
			}					
		});
	}
});

How to use

1. Import gwtmobile-persistence project into Eclipse.

• [Optional]Copy the latest persistence source code lib/persistence.js, lib/persistence.store.sql.js and lib/persistence.store.websql.js into folder gwtmobile-persistence/src/com/touchonmobile/gwtmobile/persistence/public, replacing existing files.

• In Eclipse, export gwtmobile-persistence as an JAR file.

• Create your GWT project in Eclipse.

• Add the gwtmobile-persistence JAR file as an external library to your project.

• Update your project configure file (.gwt.xml) to include the following:

    <script src="http://code.google.com/apis/gears/gears_init.js" />  <!-- Include this line only if you use Google Gears database.-->
    <inherits name='com.gwtmobile.persistence.gwtmobile_persistence' />
  

• Now your GWT project is ready to persist objects to the browser database!

Apps that use GWT Mobile Persistence

Fantasy Predictor: Manage all you Fantasy Football teams with the help of the Fantasy Predictor. Android Market, iTunes App Store

GWT Mobile Google Group

Have questions? Post it on the GWT Mobile Google Group