Convex Database

Project-specific schema, functions, and deployment details: database-config.md. Official docs: https://docs.convex.dev/

Hard limits per transaction

Exceeding one of these fails the transaction, so design against them rather than discovering them:

Batch anything larger into a cursor-based self-scheduling internalMutation: paginate({ cursor, numItems }), then ctx.scheduler.runAfter(0, internal.x.batch, { cursor: result.continueCursor }) while !result.isDone — or use the migrations component.

Rules That Are Easy To Get Wrong

Functions

• Public: query/mutation/action. Internal: internalQuery/internalMutation/internalAction. All from ./_generated/server.
• Always set a returns validator; use returns: v.null() when the function returns nothing (JS implicitly returns null).
• Pass function references (api.file.fn, internal.file.fn from ./_generated/api) to ctx.runQuery/runMutation/runAction — never the function itself.

Queries

• Do not use .filter(). Convex's .filter() performs the same as filtering in JS — neither pushes the predicate to storage. Only .withIndex()/.withSearchIndex() reduce documents scanned.
• Queries have no .delete(): collect results, then ctx.db.delete(row._id) per row.
• .unique() for single-document reads.

Mutations

• Skip no-op writes: compare before ctx.db.patch() — an unchanged write still costs invalidation, replication, and trigger execution.
• Mutations are ACID transactional; use actions for external API calls and side effects.
• Breaking schema changes need widen-migrate-narrow across two deploys (widen, migrate, then narrow).

Actions

• ctx.db does not exist in actions — use ctx.runQuery/ctx.runMutation.
• Files containing actions that use Node.js built-in modules need "use node"; at the top.

Schema

• Index names must list every field: ["team", "user"] → by_team_and_user. Index fields must be queried in definition order.
• Never define _id or _creationTime — they are automatic system fields.
• Prefer one compound index over redundant single-field indexes (by_team_and_user also serves by_team queries).
• Use v.null(), never v.undefined() — undefined is not a valid Convex value.

Components

• Components cannot access ctx.auth or process.env. Resolve both in the app and pass values across.
• Parent-app IDs cross the boundary as v.string(), not v.id("parentTable").
• Import query/mutation/action from the component's own ./_generated/server.

Environment

• Set Convex env vars in the dashboard or with npx convex env set; read them with process.env in actions only.

Deploy Loop

npx convex dev (long-running watcher, interactive on first run — ask the user to run it) → verify → npx convex deploy. If a deploy goes wrong, roll back by npx convex import of the last good export, fix locally, re-deploy.