# Cursor Plugin Convex Rule Query Optimization

> Use indexes instead of filter() for efficient database queries

- Skill: `kunanonj/cursor-plugin-convex-rule-query-optimization` (Agent Skill)
- Install (CLI): `npx skillmds@latest add kunanonj/cursor-plugin-convex-rule-query-optimization`
- Raw SKILL.md: https://api.skillmd.com/api/skills/kunanonj/cursor-plugin-convex-rule-query-optimization/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: KunanonJ (https://skillmd.com/u/kunanonj)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/kunanonj/cursor-plugin-convex-rule-query-optimization

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# Query Optimization

Avoid using `.filter()` on database queries. Instead, use indexed queries with `.withIndex()` or filter in TypeScript after collecting results.

## Why

Using `.filter()` on queries performs a full table scan, which becomes slow as your data grows. Indexes provide fast lookups.

## Examples

**Bad:**
```typescript
const user = await ctx.db
  .query("users")
  .filter(q => q.eq(q.field("email"), email))
  .first();
```

**Good:**
```typescript
// In schema.ts
export default defineSchema({
  users: defineTable({
    email: v.string(),
    name: v.string(),
  }).index("by_email", ["email"]),
});

// In your function
const user = await ctx.db
  .query("users")
  .withIndex("by_email", q => q.eq("email", email))
  .first();
```

## For Small Result Sets

If you must filter by a field that doesn't warrant an index:
```typescript
const allUsers = await ctx.db.query("users").collect();
const filtered = allUsers.filter(user => user.age > 18);
```