05-review-window-indexeddb

Review: window.indexedDB

Everything related to IndexedDB is accessed either directly or indirectly through window.indexedDB*.

Opening databases

In our application, we start by requesting an IndexedDB database named todos be opened.

var request = indexedDB.open('todos', version);

Current syntax**

IDBOpenDBRequest open (DOMString name, [EnforceRange] optional unsigned long long version);

When open is called, if a database of this name already exists, the browser will give us that - if not, it will create a new one. If the database is successfully opened a success event will be fired on the IDBOpenDBRequest object.

The version parameter allows us to be able to change the schema of the database. If we want to add or remove 'tables' (called Object Stores) we must implement the logic for doing that within onupgradeneeded. Note, the only time browser will let us add, remove or edit the structure of Object Stores is within the onupgradeneeded callback.

Note: upgradeneeded events will fire when the database is first created as well as when the version number has changed. In addition to the 'just created' cas' if your database has changed more than once (for example, if the current verson is 3) your onupgradeneeded event handler must be able to handle upgrading databases from version 1 to 3 as well as version 2 to 3. This can get quite complicated for applications whose database schemas change frequently.

var request = window.indexedDB.open("todos", 2);

request.onupgradeneeded = function(e) {
  alert("Database upgrade needed");
};

request.onsuccess = function(e) {
  alert("Database opened successfully");
};

* Documentation for this object is often filed under IDBFactory. IDBFactory is an interface that window.indexedDB implements (and indeed the only object that implements this interface).

** May be subject to change, see MDN

Deleting Databases

Deleting IndexedDB databases is also done via the window.indexedDB object via the window.indexedDB.deleteDatabase method.

Current syntax*

IDBOpenDBRequest deleteDatabase (DOMString name);

Example

var request = window.indexedDB.deleteDatabase("todos");
request.onsuccess = function(e) {
  alert("Database opened successfully");
};

* Again, may be subject to change, see MDN.

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