Using a tenantId + role three-tier model and cross-collection verification via get('database.users.openid'), implement multi-tenant read/write isolation in Database Security Rules, with a Cloud Function fallback for defense-in-depth.
From Slow Query identification to adding Indexes, avoiding Full Collection Scans, using Aggregation Pipelines instead of multiple queries, field projection, and cursor Pagination — each step explained with its underlying mechanism and applicable limits, without fabricated benchmark numbers.
After login, use the db API from @cloudbase/js-sdk to perform collection CRUD, conditional queries, and real-time watch subscriptions in a WeChat Mini Program frontend, including Permission Mode selection and unsubscribe considerations.
In a WeChat Mini Program with authentication already integrated, use db.collection().watch() to push order status updates, message alerts, and online presence sync. Covers the initial snapshot, docChanges increments, connection management, and when to call close().