B2G OS

DataStoreCursor

This API is available on Firefox OS for internal applications only.

The DataStoreCursor interface of the Data Store API represents a cursor that allows apps to iterate through a list of DataStoreTask objects representing the change history of the data store, for use when synchronizing the data.

Note: The Data Store API is available in Web Workers, from Firefox 32 onwards (Firefox OS 2.0; see bug 949325.)

Properties

DataStoreCursor.store Read only
Returns the name of the store that the cursor is iterating over.

Methods

DataStoreCursor.next()
Makes a request to retrieve information about the next operation that changes a record in the data store. Returns a Promise of type DataStoreTask.
DataStoreCursor.close()
Makes a request to terminate the cursor.

Example

In the following example, we use navigator.getDataStores to return a list of DataStore objects representing data stores on the device called contacts. Since there is only one such data store, we can access it inside the outer promise using stores[0]. The next promise uses DataStore.getLength to return the number of records in the store. If the value is 0, we populate the data store with records contained in the contactsInit object; if there is already data in the store, we run DataStore.sync to create a DataStoreCursor object allowing us to loop through any additions since the code last accessed the data store and update the data display as necessary.

The cursor is passed to the runNextTask() function, which calls DataStoreCursor.next to start the process of managing the next task — the resulting DataStoreTask object is passed to the manageTask() function to work out what to do with it. runNextTask() is then called repeatedly by manageTask() until the cursor has finished working through all the records.

navigator.getDataStores('contacts').then(function(stores) {
  stores[0].getLength().then(function(storeLength) {
    if(storeLength == 0) {
        for(i = 0; i < contactsInit.length; i++) {
        addContact(stores[0],contactsInit[i]);  
      };
    } else {
      var cursor = stores[0].sync();
      runNextTask(cursor);
    }
  });
});

function runNextTask(cursor) {
 cursor.next().then(function(task) {
   manageTask(cursor, task);
 });
}

function manageTask(cursor, task) {
  if (task.operation == 'done') {
    // Finished adding contacts!
    return;
  }

  if (task.operation == 'add') {
    // Add the contacts that are different to how it was before
    displayExisting(task.id, task.data);
  }

  runNextTask(cursor);
}

Note: This code is taken from our Data Store Contacts Editor demo. Look through the code to help you understand better what is going on, and how the full code works.

Specifications

Specification Status Comment
Data Store API
The definition of 'DataStoreCursor' in that specification.
Draft  

The discussion concerning this API's creation happened in various Mozilla mailing lists and other places. A summary of the discussion and further pointers can be found on the Mozilla Wiki. For further feedback and questions, send mail to the dev-webapi mailing list.

Browser compatibility

Supported in Firefox OS 1.0.1.
Available in web workers in Firefox OS 2.0.

See also

Document Tags and Contributors

 Contributors to this page: fscholz, chrisdavidmills
 Last updated by: fscholz,