IDBObjectStore.get() - Web APIs 编辑

The get() method of the IDBObjectStore interface returns an IDBRequest object, and, in a separate thread, returns the object store selected by the specified key. This is for retrieving specific records from an object store.

If a value is successfully found, then a structured clone of it is created and set as the result of the request object.

Note:

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.

Note:

This feature is available in Web Workers.

Syntax

var request = objectStore.get(key);

Parameters

key

The key or key range that identifies the record to be retrieved.

Return value

An IDBRequest object on which subsequent events related to this operation are fired.

Exceptions

This method may raise a DOMException of one of the following types:

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.

Example

In the following code snippet, we open a read/write transaction on our database and get one specific record from object store using get() — a sample record with the key "Walk dog". Once this data object is retrieved, you could then update it using normal JavaScript, then put it back into the database using  a IDBObjectStore.put operation. 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 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;
  };

};

Specifications

Specification	Status	Comment
Indexed Database API 2.0 The definition of 'get()' in that specification.	Recommendation
Indexed Database API 2.0 The definition of 'get()' in that specification.	Recommendation

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.)