IDBObjectStore.get()

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

js
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.)

js
// 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

BCD tables only load in the browser

参见