IDBIndex - Web APIs 编辑

IDBIndex interface of the IndexedDB API provides asynchronous access to an index in a database. An index is a kind of object store for looking up records in another object store, called the referenced object store. You use this interface to retrieve data.

You can retrieve records in an object store through the primary key or by using an index. An index lets you look up records in an object store using properties of the values in the object stores records other than the primary key

The index is a persistent key-value storage where the value part of its records is the key part of a record in the referenced object store. The records in an index are automatically populated whenever records in the referenced object store are inserted, updated, or deleted. Each record in an index can point to only one record in its referenced object store, but several indexes can reference the same object store. When the object store changes, all indexes that refers to the object store are automatically updated.

You can grab a set of keys within a range. To learn more, see IDBKeyRange.

Note:

Properties

IDBIndex.isAutoLocale Read only

Returns a Boolean indicating whether the index had a locale value of auto specified upon its creation (see createIndex()'s optionalParameters.)

IDBIndex.locale Read only

Returns the locale of the index (for example en-US, or pl) if it had a locale value specified upon its creation (see createIndex()'s optionalParameters.)

IDBIndex.name

The name of this index.

IDBIndex.objectStore Read only

The name of the object store referenced by this index.

IDBIndex.keyPath Read only

The key path of this index. If null, this index is not auto-populated.

IDBIndex.multiEntry Read only

Affects how the index behaves when the result of evaluating the index's key path yields an array. If true, there is one record in the index for each item in an array of keys. If false, then there is one record for each key that is an array.

IDBIndex.unique Read only

If true, this index does not allow duplicate values for a key.

Methods

Inherits from: EventTarget

IDBIndex.count()

Returns an IDBRequest object, and in a separate thread, returns the number of records within a key range.

IDBIndex.get()

Returns an IDBRequest object, and, in a separate thread, finds either the value in the referenced object store that corresponds to the given key or the first corresponding value, if key is an IDBKeyRange.

IDBIndex.getKey()

Returns an IDBRequest object, and, in a separate thread, finds either the given key or the primary key, if key is an IDBKeyRange.

IDBIndex.getAll()

Returns an IDBRequest object, in a separate thread, finds all matching values in the referenced object store that correspond to the given key or are in range, if key is an IDBKeyRange.

IDBIndex.getAllKeys()

Returns an IDBRequest object, in a separate thread, finds all matching keys in the referenced object store that correspond to the given key or are in range, if key is an IDBKeyRange.

IDBIndex.openCursor()

Returns an IDBRequest object, and, in a separate thread, creates a cursor over the specified key range.

IDBIndex.openKeyCursor()

Returns an IDBRequest object, and, in a separate thread, creates a cursor over the specified key range, as arranged by this index.

Example

In the following example we open a transaction and an object store, then get the index lName from a simple contacts database. We then open a basic cursor on the index using IDBIndex.openCursor — this works the same as opening a cursor directly on an ObjectStore using IDBObjectStore.openCursor except that the returned records are sorted based on the index, not the primary key.

Finally, we iterate through each record, and insert the data into an HTML table. For a complete working example, see our IndexedDB-examples demo repo (View the example live.)

function displayDataByIndex() {
  tableEntry.innerHTML = '';
  var transaction = db.transaction(['contactsList'], 'readonly');
  var objectStore = transaction.objectStore('contactsList');

  var myIndex = objectStore.index('lName');
  myIndex.openCursor().onsuccess = function(event) {
    var cursor = event.target.result;
    if(cursor) {
      var tableRow = document.createElement('tr');
      tableRow.innerHTML =   '<td>' + cursor.value.id + '</td>'
                           + '<td>' + cursor.value.lName + '</td>'
                           + '<td>' + cursor.value.fName + '</td>'
                           + '<td>' + cursor.value.jTitle + '</td>'
                           + '<td>' + cursor.value.company + '</td>'
                           + '<td>' + cursor.value.eMail + '</td>'
                           + '<td>' + cursor.value.phone + '</td>'
                           + '<td>' + cursor.value.age + '</td>';
      tableEntry.appendChild(tableRow);

      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.)