database

Conventions for using PostgreSQL, a relational database, and for writing database migrations, which are controlled changes to a database's structure.

In plain words
What is it for?
Use them when adding tables or columns, changing constraints, creating relationships, choosing PostgreSQL data types, or preparing migrations for existing data.
Why use it?
They help keep schema changes reversible, indexed, linked correctly, and safe to apply while the application is running.

Cursor rule for Cursor

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/romkey/i2c-directory/database
Clone the repo
git clone --depth 1 https://github.com/romkey/I2C-Directory

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 285 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00000 $0.00285
Opus 5 $0.00000 $0.00143
Sonnet 5 $0.00000 $0.00057
Haiku 4.5 $0.00000 $0.00028

Measured yesterday against content hash 422852495c33, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

database scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.cursor/rules/database.mdc · 30 lines

What it actually says

Database and Migrations

  • Database: PostgreSQL 16
  • Adapter: pg gem with connection via DATABASE_URL or individual DB_HOST/DB_PORT/DB_USERNAME/DB_PASSWORD env vars

Migration Conventions

  • Always provide a reversible migration or implement both up and down methods
  • Use add_index for columns used in WHERE, ORDER BY, or JOIN clauses
  • Use add_reference with foreign_key: true for associations
  • Prefer change_column_null over allowing nullable columns by default — be explicit
  • Use PostgreSQL-specific types when beneficial: citext for case-insensitive text, jsonb for JSON data, uuid for external IDs
  • Add NOT NULL constraints with defaults for new required columns on existing tables to avoid downtime
# ✅ Safe addition of a required column to an existing table
class AddStatusToMembers < ActiveRecord::Migration[8.0]
  def change
    add_column :members, :status, :string, null: false, default: 'active'
    add_index :members, :status
  end
end
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 30 lines · 0 tokens per session scan A 422852495c33

Subscribe to this mod's changes

database is a cursor rule published in the GitHub repository romkey/I2C-Directory (11 stars, last pushed 21d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 285 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.