Dojo: The Definitive Guide

Data API Overview

The most basic atom of the dojo.data API is called an item, which is composed of key/value pairs called attributes and attribute values in dojo.data parlance; conceptually, you can think of an item as a plain old JavaScript Object. However, although the underlying implementation may very well be a JavaScript Object, be careful to use the provided APIs for accessing it, as the internal representation may be something entirely different. For example, some data abstractions may use a DOM model for storing certain types of data for efficiency reasons, or lazy-load data on the fly even though it seems like it's already local. In cases like these, accessing an item like a plain old JavaScript object would likely cause an unexpected error. We'll come back to specific API calls for accessing an item in the next section.

Tip

Saying that an item has an attribute—but no value for the attribute—is the same as saying that the item doesn't have the attribute at all. In other words, it's nonsensical to think about having an attribute with no value because attributes inherently have a specific state.

Before getting into the capabilities of any one specific API, it's helpful to survey the landscape. Here's an overview of the various dojo.data APIs with a brief summary of what these APIs provide to the application developer. These APIs are interfaces, not implementations; any concrete dojo.data data store would define one or more of the upcoming APIs:

dojo.data.api.Read

Provides a uniform means of reading, searching, sorting, and filtering data items.

dojo.data.api.Write

Provides a uniform means of creating, deleting, and updating data items.

dojo.data.api.Identity

Provides a uniform means of accessing an item via a unique identifier.

dojo.data.api.Notification

Provides a uniform means of notifying a listener of a change, such as create, delete, or update operation, for a data item.

The remainder of this chapter systematically works through each of these APIs and provides plenty of examples so that you can make the most of dojo.data in your own application.