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IDBIndex.unique

The unique read-only property returns a boolean that states whether the index allows duplicate keys.

This is decided when the index is created, using the IDBObjectStore.createIndex method. This method takes an optional parameter, unique, which if set to true means that the index will not be able to accept duplicate entries.

Note: This feature is available in Web Workers.

Syntax

var isUnique = IDBIndex.unique; 

Value

A Boolean:

Value Effect
true The current index does not allow duplicate values for a key.
false The current index allows duplicate key values.

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.

The unique status of the index is logged to the console: it should be returned as false.

Finally, we iterate through each record, and insert the data into an HTML table. For a complete working example, see our IDBIndex-example 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'); 
  console.log(myIndex.unique);

  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.');    
    }
  };
};

Specification

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 23webkit
24 (unprefixed)
(Yes) 10 moz
16.0 (16.0)
10, partial 15 7.1
Available in workers (Yes) (Yes) 37.0 (37.0) ? (Yes) ?
Indexed Database 2.0 58 ? ? ? 54 ?
Feature Android Webview Chrome for Android Edge Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) 22.0 (22.0) 1.0.1 10 22 8
Available in workers (Yes) (Yes) (Yes) 37.0 (37.0) (Yes) ? (Yes) ?
Indexed Database 2.0 58 58 ? ? ? ? 54 ?

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/IDBIndex/unique