Firestore

Firestore is Google Cloud's fully managed, serverless, document-oriented NoSQL database. It is the successor to the original Cloud Datastore and is designed for building web, mobile, and server applications that need real-time synchronisation, offline support, and automatic scaling to zero.

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What Is Firestore?

Firestore is a flexible, scalable NoSQL document database that provides:

• Document-collection model — data is organised into collections of documents, each containing key-value pairs.
• Real-time listeners — clients receive instant updates when data changes.
• Offline support — SDKs cache data locally, enabling offline reads and writes that sync when connectivity returns.
• Serverless — no instances to manage; scales automatically from zero to millions of operations.
• ACID transactions — multi-document transactions across collections.
• Strong consistency — all reads return the latest committed data.

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Data Model

Documents and Collections

• A document is a set of key-value pairs (similar to a JSON object). Each document has a unique ID within its collection.
• A collection is a container for documents. Collections can only contain documents (no nested collections directly — but documents can contain subcollections).

Example

graph TD
  A["users (collection)"] --> B["user-123 (document)"]
  B --> C["name: Alice"]
  B --> D["email: alice@example.com"]
  B --> E["orders (subcollection)"]
  E --> F["order-001 (document)"]
  F --> G["product: Widget"]
  F --> H["quantity: 3"]
  F --> I["total: 29.97"]

Data Types

Firestore supports strings, numbers, booleans, dates, geopoints, arrays, maps (nested objects), references (pointers to other documents), and null values.

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Querying

Firestore provides rich querying capabilities:

• Simple queries — filter by field value, range, or array membership.
• Composite queries — combine multiple conditions (requires a composite index).
• Collection group queries — query across all subcollections with the same name.
• Order and limit — sort results and paginate.
• IN and array-contains — flexible matching operators.

Indexes

Firestore automatically creates single-field indexes for every field. For queries with multiple filters or ordering, you create composite indexes. Firestore will tell you when a composite index is needed and provide a link to create it.

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Real-Time Listeners

One of Firestore's most powerful features is real-time synchronisation:

• Clients register a listener on a document or query.
• When the data changes, the listener fires immediately with the updated snapshot.
• This enables live dashboards, collaborative editing, chat applications, and live notifications.

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