Indexes and queries

Learn to add an index to an object store and run range queries.

Creating an index

An index lets you search quickly by a field inside an object store. It is created with store.createIndex(name, keyPath); you can then run get, getAll or cursor queries against it.

const index = store.createIndex('by_date', 'date');

Here 'by_date' is the index name and 'date' is the indexed field. You can now look up records by their date field.

Range queries with IDBKeyRange

IDBKeyRange defines a range of keys and is used in index queries. For example IDBKeyRange.only(x) matches only x, while IDBKeyRange.lowerBound(y) covers y and above.

const range = IDBKeyRange.only('2024-01-01');
index.getAll(range);

This way you can fetch all records matching a specific date or a numeric range in one call.

Exercise Create store and index

Assign a function to request.onupgradeneeded. Inside, read event.target.result into a db variable. Create the 'notes' store with db.createObjectStore and { keyPath: 'id' }, assign it to store. Then call store.createIndex to create the 'by_date' index on the 'date' keyPath.

Show example solution

request.onupgradeneeded = function(event) {
  const db = event.target.result;
  const store = db.createObjectStore('notes', { keyPath: 'id' });
  store.createIndex('by_date', 'date');
};

Test yourself

What does an index provide?
- It bumps the database version
- It deletes all records
- It creates a new object store
- Fast lookups by a specific field
Show answer

Fast lookups by a specific field — Correct! An index enables fast lookups by a field.

Create an index

const index = store.____('by_date', 'date');

Show answer

const index = store.createIndex('by_date', 'date');

Match index terms

createIndex

create an index
IDBKeyRange

key range
index.getAll

fetch all matches
index.get

fetch one record

Next lesson: Summary - IndexedDB

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