IDBCursor - Web APIs 编辑

Note: Not to be confused with IDBCursorWithValue which is just an IDBCursor interface with an additional value property.

The IDBCursor interface of the IndexedDB API represents a cursor for traversing or iterating over multiple records in a database.

The cursor has a source that indicates which index or object store it is iterating over. It has a position within the range, and moves in a direction that is increasing or decreasing in the order of record keys. The cursor enables an application to asynchronously process all the records in the cursor's range.

You can have an unlimited number of cursors at the same time. You always get the same IDBCursor object representing a given cursor. Operations are performed on the underlying index or object store.

Note:

Properties

Note: IDBCursorWithValue is an IDBCursor interface with an additional value property.

IDBCursor.source Read only

Returns the IDBObjectStore or IDBIndex that the cursor is iterating. This function never returns null or throws an exception, even if the cursor is currently being iterated, has iterated past its end, or its transaction is not active.

IDBCursor.direction Read only

Returns the direction of traversal of the cursor. See Constants for possible values.

IDBCursor.key Read only

Returns the key for the record at the cursor's position. If the cursor is outside its range, this is set to undefined. The cursor's key can be any data type.

IDBCursor.primaryKey Read only

Returns the cursor's current effective primary key. If the cursor is currently being iterated or has iterated outside its range, this is set to undefined. The cursor's primary key can be any data type.

IDBCursor.request Read only

Returns the IDBRequest that was used to obtain the cursor.

Methods

IDBCursor.advance()

Sets the number of times a cursor should move its position forward.

IDBCursor.continue()

Advances the cursor to the next position along its direction, to the item whose key matches the optional key parameter.

IDBCursor.continuePrimaryKey()

Sets the cursor to the given index key and primary key given as arguments.

IDBCursor.delete()

Returns an IDBRequest object, and, in a separate thread, deletes the record at the cursor's position, without changing the cursor's position. This can be used to delete specific records.

IDBCursor.update()

Returns an IDBRequest object, and, in a separate thread, updates the value at the current position of the cursor in the object store. This can be used to update specific records.

Constants

Deprecated since Gecko 13 (Firefox 13 / Thunderbird 13 / SeaMonkey 2.10)

This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

These constants are no longer available — they were removed in Gecko 25. You should use the string constants directly instead. (bug 891944)

• NEXT: "next" : The cursor shows all records, including duplicates. It starts at the lower bound of the key range and moves upwards (monotonically increasing in the order of keys).
• NEXTUNIQUE : "nextunique" : The cursor shows all records, excluding duplicates. If multiple records exist with the same key, only the first one iterated is retrieved. It starts at the lower bound of the key range and moves upwards.
• PREV: "prev" : The cursor shows all records, including duplicates. It starts at the upper bound of the key range and moves downwards (monotonically decreasing in the order of keys).
• PREVUNIQUE: "prevunique" : The cursor shows all records, excluding duplicates. If multiple records exist with the same key, only the first one iterated is retrieved. It starts at the upper bound of the key range and moves downwards.

Examples

In this simple fragment we create a transaction, retrieve an object store, then use a cursor to iterate through all the records in the object store. The cursor does not require us to select the data based on a key; we can just grab all of it. Also note that in each iteration of the loop, you can grab data from the current record under the cursor object using cursor.value.foo. For a complete working example, see our IDBCursor example (view example live.)

function displayData() {
  var transaction = db.transaction(['rushAlbumList'], "readonly");
  var objectStore = transaction.objectStore('rushAlbumList');

  objectStore.openCursor().onsuccess = function(event) {
    var cursor = event.target.result;
    if(cursor) {
      var listItem = document.createElement('li');
      listItem.innerHTML = cursor.value.albumTitle + ', ' + cursor.value.year;
      list.appendChild(listItem);

      cursor.continue();
    } else {
      console.log('Entries all displayed.');
    }
  };
}

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.)