IDBRequest.transaction - Web APIs 编辑

The transaction read-only property of the IDBRequest interface returns the transaction for the request, that is, the transaction the request is being made inside.

This property can be null for requests not made within transactions, such as for requests returned from IDBFactory.open — in this case you're just connecting to a database, so there is no transaction to return. If a version upgrade is needed when opening a database then during the upgradeneeded event handler the transaction property will be an IDBTransaction with mode equal to "versionchange", and can be used to access existing object stores and indexes, or abort the upgrade. Following the upgrade, the transaction property will again be null.

Note:

Syntax

var myTransaction = request.transaction;

Value

An IDBTransaction.

Example

The following example requests a given record title, onsuccess gets the associated record from the IDBObjectStore (made available as objectStoreTitleRequest.result), updates one property of the record, and then puts the updated record back into the object store in another request. The source of the requests is logged to the developer console — both originate from the same transaction. For a full working example, see our To-do Notifications app (view example live.)

var title = "Walk dog";

// Open up a transaction as usual
var objectStore = db.transaction(['toDoList'], "readwrite").objectStore('toDoList');

// Get the to-do list object that has this title as it's title
var objectStoreTitleRequest = objectStore.get(title);

objectStoreTitleRequest.onsuccess = function() {
  // Grab the data object returned as the result
  var data = objectStoreTitleRequest.result;

  // Update the notified value in the object to "yes"
  data.notified = "yes";

  // Create another request that inserts the item back
  // into the database
  var updateTitleRequest = objectStore.put(data);

  // Log the transaction that originated this request
  console.log("The transaction that originated this request is " + updateTitleRequest.transaction);

  // When this new request succeeds, run the displayData()
  // function again to update the display
  updateTitleRequest.onsuccess = function() {
    displayData();
  };
};

This example shows how a the transaction property can be used during a version upgrade to access existing object stores:

var openRequest = indexedDB.open('db', 2);
console.log(openRequest.transaction); // Will log "null".

openRequest.onupgradeneeded = function(event) {
  console.log(openRequest.transaction.mode); // Will log "versionchange".
  var db = openRequest.result;
  if (event.oldVersion < 1) {
    // New database, create "books" object store.
    db.createObjectStore('books');
  }
  if (event.oldVersion < 2) {
    // Upgrading from v1 database: add index on "title" to "books" store.
    var bookStore = openRequest.transaction.objectStore('books');
    bookStore.createIndex('by_title', 'title');
  }
};

openRequest.onsuccess = function() {
  console.log(openRequest.transaction); // Will log "null".
};

Specifications

Browser compatibility

BCD tables only load in the browser

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.)