IDBObjectStore.get()
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since 2015年7月.
IDBObjectStore 的接口 **get()**方法 返回 IDBRequest 对象，并在“单独的线程（separate thread）”中返回由指定键选择的“对象储存（object store）” 。这用于从对象储存检索特定记录。
如果成功找到值，则会创建其值的结构化克隆，并设置为“请求对象（request object）”的 result 。
备注：This method produces the same result for: a) a record that doesn't exist in the database and b) a record that has an undefined value. To tell these situations apart, call the openCursor() method with the same key. That method provides a cursor if the record exists, and no cursor if it does not.
备注： 此特性在 Web Worker 中可用。
语法
get(key)
参数
- key
-
标识要检索的记录的键或键范围。
返回值
触发与此操作相关的后续事件的 IDBRequest 对象。
异常
此方法可能会引发以下类型之一的 DOMException :
| Exception | Description |
|---|---|
| TransactionInactiveError | This IDBObjectStore's transaction is inactive. |
| DataError | The key or key range provided contains an invalid key. |
InvalidStateError |
The IDBObjectStore has been deleted or removed. |
示例
在以下的代码段中，我们在数据库上打开一个“读/写 事务（read/write transaction）”，并使用 get() 从“对象储存（object store）”中获取一个特定的记录——一个带有“Walk dog”键的示例记录。一旦检索到这个数据对象，你就可以使用普通的 JavaScript 更新它，然后使用 IDBObjectStore.put 操作将其放回数据库。有关完整的工作示例，查看我们的 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 getData() function to get the data from the database
getData();
};
function getData() {
// open a read/write db transaction, ready for retrieving the data
var transaction = db.transaction(["toDoList"], "readwrite");
// report on the success of the transaction completing, when everything is done
transaction.oncomplete = function (event) {
note.innerHTML += "<li>Transaction completed.</li>";
};
transaction.onerror = function (event) {
note.innerHTML +=
"<li>Transaction not opened due to error: " + transaction.error + "</li>";
};
// create an object store on the transaction
var objectStore = transaction.objectStore("toDoList");
// Make a request to get a record by key from the object store
var objectStoreRequest = objectStore.get("Walk dog");
objectStoreRequest.onsuccess = function (event) {
// report the success of our request
note.innerHTML += "<li>Request successful.</li>";
var myRecord = objectStoreRequest.result;
};
}
规范
| Specification |
|---|
| Indexed Database API 3.0 # ref-for-dom-idbobjectstore-get① |
浏览器兼容性
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参见
- 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.)