The IDBTransaction
interface of the IndexedDB API provides a static, asynchronous transaction on a database using event handler attributes. All reading and writing of data is done within transactions. You actually use IDBDatabase
to start transactions and IDBTransaction
to set the mode of the transaction (e.g. is it readonly or readwrite), and access an IDBObjectStore
to make a request. You can also use it to abort transactions.
Note that as of Firefox 40, IndexedDB transactions have relaxed durability guarantees to increase performance (see bug 1112702.) Previously in a readwrite
transaction IDBTransaction.oncomplete
was fired only when all data was guaranteed to have been flushed to disk. In Firefox 40+ the complete
event is fired after the OS has been told to write the data but potentially before that data has actually been flushed to disk. The complete
event may thus be delivered quicker than before, however, there exists a small chance that the entire transaction will be lost if the OS crashes or there is a loss of system power before the data is flushed to disk. Since such catastrophic events are rare most consumers should not need to concern themselves further.
If you must ensure durability for some reason (e.g. you're storing critical data that cannot be recomputed later) you can force a transaction to flush to disk before delivering the complete
event by creating a transaction using the experimental (non-standard) readwriteflush
mode (see IDBDatabase.transaction
.
Note that transactions are started when the transaction is created, not when the first request is placed; for example consider this:
var trans1 = db.transaction("foo", "readwrite"); var trans2 = db.transaction("foo", "readwrite"); trans2.put("2", "key"); trans1.put("1", "key");
After the code is executed the object store should contain the value "2", since trans2
should run after trans1
.
Methods
Inherits from: EventTarget
IDBTransaction.abort
- Rolls back all the changes to objects in the database associated with this transaction. If this transaction has been aborted or completed, then this method throws an error event.
IDBTransaction.objectStore
- Returns an
IDBObjectStore
object representing an object store that is part of the scope of this transaction.
Properties
IDBTransaction.db
Read only- The database connection with which this transaction is associated.
IDBTransaction.mode
Read only- The mode for isolating access to data in the object stores that are in the scope of the transaction. For possible values, see the Constants section below. The default value is
readonly
. IDBTransaction.objectStoreNames
Read only- Returns a
DOMStringList
of the names ofIDBObjectStore
objects. IDBTransaction.error
Read only- Returns one of several types of error when there is an unsuccessful transaction. This property is
null
if the transaction is not finished, is finished and successfully committed, or was aborted withIDBTransaction.abort
function.
Event handlers
IDBTransaction.onabort
Read only- The event handler for the
abort
event, fired when the transaction is aborted. IDBTransaction.oncomplete
Read only- The event handler for the
complete
event, thrown when the transaction completes successfully. IDBTransaction.onerror
Read only- The event handler for the
error
event, thrown when the transaction fails to complete.
Mode constants
Deprecated since Gecko 13 (Firefox 13 / Thunderbird 13 / SeaMonkey 2.10)
This feature has been removed from the Web standards. Though some browsers may still support it, it is in the process of being dropped. Do not use it in old or new projects. Pages or Web apps using it may break at any time.
These constants are no longer available — they were removed in Gecko 25. You should use the string constants directly instead. (bug 888598)
Transactions can have one of three modes:
Constant | Value | Description |
---|---|---|
READ_ONLY |
"readonly" (0 in Chrome) |
Allows data to be read but not changed. |
READ_WRITE |
"readwrite" (1 in Chrome) |
Allows reading and writing of data in existing data stores to be changed. |
VERSION_CHANGE |
"versionchange" (2 in Chrome) |
Allows any operation to be performed, including ones that delete and create object stores and indexes. This mode is for updating the version number of transactions that were started using the setVersion() method of IDBDatabase objects. Transactions of this mode cannot run concurrently with other transactions. |
Even if these constants are now deprecated, you can still use them to provide backward compatibility if required (in Chrome the change was made in version 21). You should code defensively in case the object is not available anymore:
var myIDBTransaction = window.IDBTransaction || window.webkitIDBTransaction || { READ_WRITE: "readwrite" };
Example
In the following code snippet, we open a read/write transaction on our database and add some data to an object store. Note also the functions attached to transaction event handlers to report on the outcome of the transaction opening in the event of success or failure. For a full working example, see our To-do Notifications app (view example live.)
// Let us open our database var DBOpenRequest = window.indexedDB.open("toDoList", 4); DBOpenRequest.onsuccess = function(event) { note.innerHTML += '<li>Database initialised.</li>'; // store the result of opening the database in the db variable. This is used a lot below db = DBOpenRequest.result; // Run the addData() function to add the data to the database addData(); }; function addData() { // Create a new object ready for being inserted into the IDB var newItem = [ { taskTitle: "Walk dog", hours: 19, minutes: 30, day: 24, month: "December", year: 2013, notified: "no" } ]; // open a read/write db transaction, ready for adding the data var transaction = db.transaction(["toDoList"], "readwrite"); // report on the success of opening the transaction transaction.oncomplete = function(event) { note.innerHTML += '<li>Transaction completed: database modification finished.</li>'; }; transaction.onerror = function(event) { note.innerHTML += '<li>Transaction not opened due to error. Duplicate items not allowed.</li>'; }; // create an object store on the transaction var objectStore = transaction.objectStore("toDoList"); // add our newItem object to the object store var objectStoreRequest = objectStore.add(newItem[0]); objectStoreRequest.onsuccess = function(event) { // report the success of our new item going into the database note.innerHTML += '<li>New item added to database.</li>'; }; };
Specifications
Specification | Status | Comment |
---|---|---|
Indexed Database API The definition of 'IDBTransaction' in that specification. |
Recommendation | Initial definition |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|
Basic support | 23webkit 24[1] |
10 moz 16.0 (16.0) |
10, partial | 15 | 7.1 |
Available in workers | (Yes) | 37.0 (37.0) | ? | (Yes) | ? |
objectStoreNames property |
48.0 | No support | No support | No support | No support |
Feature | Android | Android Webview | Firefox Mobile (Gecko) | Firefox OS | IE Phone | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|---|
Basic support | 4.4 | (Yes) | 22.0 (22.0) | 1.0.1 | 10 | 22 | 8 | (Yes) |
Available in workers | (Yes) | (Yes) | 37.0 (37.0) | (Yes) | ? | (Yes) | ? | (Yes) |
objectStoreNames property |
No support | 48.0 | No support | No support | No support | No support | No support | 48.0 |
- [1] Older versions of Chrome serialize all transactions. So even if you have only read-only transactions and no read-write transaction, your transactions are executed one at a time. Any subsequent transactions are not executed until all read-only transactions are completed. For the status, see bug 64076.
See also
- Using IndexedDB
- Starting transactions:
IDBDatabase
- Using transactions:
IDBTransaction
- Setting a range of keys:
IDBKeyRange
- Retrieving and making changes to your data:
IDBObjectStore
- Using cursors:
IDBCursor
- Reference example: To-do Notifications (view example live.)