There is growing support in browsers for offline capabilities with the HTML 5 specification for local storage, offline notifications, and offline application cache, but adapting an application to store changes locally and do synchronization when connectivity is restored remains a major challenge for developers. Dojo 1.2’s new dojox.rpc.OfflineRest module automates the local storage of data and synchronization by leveraging the Dojo Data and REST abstractions. The OfflineRest module augments the JsonRest service in Dojo such that requests are cached in local storage for offline access, and modification requests (put, post, and delete) modify the cache and are recorded for delivery to the server; immediately if online, otherwise when connectivity is restored. Furthermore, JsonRest is the core engine used by JsonRestStore. Consequently, you can simply use the standard Dojo Data API with the JsonRestStore and effortlessly add offline capability with no modifications to your data interaction code. The underlying Rest service automates the handling of caching, storing data locally, and syncing changes. In addition the new OfflineRest module has no dependency on plugins, but rather progressively utilizes offline features that are available, while still operating properly on legacy browsers without offline support.

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Non-trivial data often has structures that cannot be well-defined with normal linear, acyclic data descriptions. Data that consists of cycles, many-to-one relationships, and non-local references often requires custom strategies for serialization and transfer of the data over JSON. Dojo 1.2 has added support for JSON referencing with the dojox.json.ref module. This module provides support for several forms of referencing including circular, multiple, inter-message, and lazy referencing using id, path, and combined referencing forms.

These references can be automatically generated on serialization and resolved on deserialization. JSON referencing is designed to decouple the topology of data structures from the meaning of the data structures in a way that is consistent with runtime object models of modern OO languages (foremost JavaScript). Separating graph connectedness concerns allows referencing and dereferencing to be handled by dojox.json.ref with minimal or no knowledge of and integration with higher level JSON consumers and producers, and permits more extensive JavaScript serialization capabilities.

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Dojo 1.2 now includes an infrastructure for interacting with JSON REST services and data storage systems. JsonRestStore is a new Dojo Data store for interacting with the RESTful JSON data sources. This new data store allows you to communicate with server side database/persistent data storage using the Dojo Data API with JavaScript and efficiently handles create, read, update, and delete (CRUD) operations. This can greatly simplify client server communication, interacting can be done simply using straightforward JavaScript instead of having to build your communication for CRUD actions. In addition, Dojo data stores can plugin to many Dojo widgets (Dijits).

Complex database driven widgets can be utilized with minimal coding effort. RESTful JSON is an increasingly popular database interface, and in later posts we will look at how JsonRestStore can be used with Amazon S3, CouchDB, Persevere, and Ruby on Rails. The JsonRestStore fully implements the Dojo Data read, write, notification, and identity interfaces. Therefore it can be used with any widget that can utilize these data stores including widgets with editing and live auto-updating features.

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