IDBTransaction は IndexedDB API のインターフェイスで、イベントハンドラー属性を使用してデータベース上の静的で非同期のトランザクションを提供します。すべてのデータの読み書きはトランザクション内で行われます。 {{domxref("IDBDatabase")}} を使用してトランザクションを開始し、 {{domxref("IDBTransaction")}} を使用してトランザクションのモードを設定し (例 readonly または readwrite)、 {{domxref("IDBObjectStore")}} にアクセスしてリクエストを作成します。 IDBTransaction オブジェクトを使用してトランザクションを中止することもできます。
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トランザクションは、最初のリクエストが発行された時ではなく、トランザクションが生成されたときに開始します。例えば、次のものを考えてください。
var trans1 = db.transaction("foo", "readwrite");
var trans2 = db.transaction("foo", "readwrite");
var objectStore2 = trans2.objectStore("foo")
var objectStore1 = trans1.objectStore("foo")
objectStore2.put("2", "key");
objectStore1.put("1", "key");
このコードが実行された後で、オブジェクトストアには "2" が含まれているはずであり、これは trans2 が trans1 の後に実行されるからです。
トランザクションは一定数の理由で失敗することがあり、 (ユーザーエージェントのクラッシュを除いて) すべての場合に abort コールバックを起動します。
add() the same key twice, or put() with the same index key with a uniqueness constraint. This causes an error on the request, which can bubble up to an error on the transaction, which aborts the transaction. This can be prevented by using preventDefault() on the error event on the request.abort() call from script.success/error handler.Note that as of Firefox 40, IndexedDB transactions have relaxed durability guarantees to increase performance (see {{Bug("1112702")}}.) Previously in a readwrite transaction {{domxref("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 {{domxref("IDBDatabase.transaction")}}.
null if the transaction is not finished, is finished and successfully committed, or was aborted with the{{domxref("IDBTransaction.abort()")}} function.readonly.Inherits from: {{domxref("EventTarget")}}
commit() can be used to start the commit process without waiting for events from outstanding requests to be dispatched.Listen to these events using addEventListener() or by assigning an event listener to the oneventname property of this interface.
abortIndexedDB transaction is aborted.onabort property.completeoncomplete property.erroronerror property.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:
| 定数 | 値 | 説明 |
|---|---|---|
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. Transactions in this mode are known as "upgrade 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" };
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;
// Add the data to the database
addData();
};
function addData() {
// Create a new object to insert 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 to add 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 the request (this does not mean the item
// has been stored successfully in the DB - for that you need transaction.oncomplete)
note.innerHTML += '<li>Request successful.</li>';
};
};
| 仕様書 | 状態 | 備考 |
|---|---|---|
| {{SpecName('IndexedDB', '#transaction', 'IDBTransaction')}} | {{Spec2('IndexedDB')}} | 初回定義 |
| {{SpecName("IndexedDB 2", "#transaction", "IDBTransaction")}} | {{Spec2("IndexedDB 2")}} |