IndexedDB

Concetti chiave ed uso

IndexedDB è un sistema di database transazionale, che inizialmente potrebbe creare confusione se si è abituati a lavorare solo con i database relazionali, ma presto diverrà abbastanza chiaro. IndexedDB permette di memorizzare e recuperare oggetti indicizzati con una chiave. E' necessario specificare lo schema del database, aprire una connessione al proprio database e poi recuperare ed aggiornare i dati attraverso una serie di transazioni.

• Apprendere maggiori info sui concetti dietro a IndexedDB.
• Imparare ad usare IndexedDB in modo asincrono dai primi principi con la nostra guida Usare IndexedDB.
• Trova le raccomandazioni degli sviluppatori per far lavorare le apps web offline alla pagina Offline Apps.

Sincrono e asincrono

IndexedDB include sia una API asincrona che una API sincrona. La API asincrona può essere usata in molti casi, incluso WebWorkers, mentre la API sincrona è designata ad essere utilizzata solo con Web Workers e sarà usata molto raramente.

Limiti di memorizzazione

Non c'è alcun limite alla dimensione di un singolo elemento del database, tuttavia ci potrebbe essere un limite ad ogni dimensione complessiva del database IndexedDB. Questo limite (ed il modo con cui l'interfaccia utente lo supporterà) potrebbe variare da un browser ad un altro:

• Firefox non ha limite sulla dimensione del database IndexedDB. The user interface will just ask permission for storing blobs bigger than 50 MB. This size quota can be customized through the dom.indexedDB.warningQuota preference (which is defined in https://mxr.mozilla.org/mozilla-central/source/modules/libpref/src/init/all.js).
• Google Chrome: see https://developers.google.com/chrome...rage#temporary.

Asynchronous API

The asynchronous API methods return without blocking the calling thread. To get asynchronous access to a database, call open() on the indexedDB attribute of a window object. This method returns an IDBRequest object; asynchronous operations communicate to the calling application by firing events on IDBRequest objects.

Connecting to a database

IDBEnvironment

Provides access to a client-side database. It is implemented by the window and worker objects.

IDBFactory

Provides access to a database. This is the interface implemented by the global object indexedDB and is therefore the entry point for the API.

IDBOpenDBRequest

Represents a request to open a database.

IDBDatabase

Represents a connection to a database. It's the only way to get a transaction on the database.

Accessing results of database requests

IDBRequest

Provides access to results of asynchronous requests to databases and database objects. It is what you get when you call an asynchronous method.

Retrieving and modifying data

IDBTransaction

Represents a transaction. You create a transaction on a database, specify the scope (such as which object stores you want to access), and determine the kind of access (read only or write) that you want.

IDBObjectStore

Represents an object store.

IDBIndex

Provides access to the metadata of an index.

IDBCursor

Iterates over object stores and indexes.

IDBCursorWithValue

Iterates over object stores and indexes and returns the cursor's current value.

IDBKeyRange

Defines a range of keys.

Deprecated interfaces

An early version of the specification also defined these now removed interfaces. They are still documented in case you need to update previously written code:

IDBVersionChangeRequest

Represents a request to change the version of a database. The way to change the version of the database has since changed (by calling IDBFactory.open without also calling IDBDatabase.setVersion), and the interface IDBOpenDBRequest now has the functionality of the removed IDBVersionChangeRequest.

IDBDatabaseException 

Represents exception conditions that can be encountered while performing database operations.

Synchronous API

To get synchronous access to a database, call open() on the Unimplemented indexedDBSync attribute of a worker object. This returns an IDBDatabaseSync object, which enables you to create, open, and remove object stores and indexes, set the version of the database, and create transactions.

• IDBCursorSync iterates over object stores and indexes.
• IDBDatabaseSync represents a connection to a database. It's the only way to get a transaction on the database.
• IDBEnvironmentSync provides access to a client-side database. It is implemented by worker objects.
• IDBFactorySync provides access to a database.
• IDBIndexSync provides access to the metadata of an index.
• IDBObjectStoreSync represents an object store.
• IDBTransactionSync creates a transaction in the database.

Examples

• eLibri: A powerful library and eBook reader application, written by Marco Castelluccio, winner of the IndexedDB Mozilla DevDerby.
• To-do Notifications (view example live): The reference application for the examples in the reference docs: Not every snippet appears in this example, but every example uses the same data structure and syntax, and will make sense in the context of this application.
• Storing images and files in IndexedDB
• IndexedDB Examples

Browser compatibility

Specifications