/database-patterns

name: database-patterns
license: MIT
compatibility: "Claude Code 2.1.277+."
description: "Schema design, Alembic migrations and database versioning. Use when creating migrations, designing or normalizing schemas, or fixing schema drift."
user-invocable: false
disable-model-invocation: false
targets:
  - library: sqlalchemy
    version: ">=2.1.1"
metadata:
  owner-agent: "database-engineer"
  category: document-asset-creation
  version: "2.0.0"
  author: "OrchestKit"
  complexity: "medium"
  tags: "database, migrations, alembic, schema-design, versioning, postgresql, sql, nosql"
allowed-tools: "Read Glob Grep WebFetch WebSearch"
paths: ["**/migrations/**", "**/models/**", "alembic.ini", "**/schema*"]
path_patterns: ["*.sql", "**/migrations/**", "**/alembic/**", "**/prisma/**"]

<!-- directive-density: intentional (teaches migration anti-patterns; NEVER markers describe real production-break conditions, not aspirational guidance) -->

Database Patterns

Comprehensive patterns for database migrations, schema design, and version management. Each category has individual rule files in `rules/` loaded on-demand.

Quick Reference

| Category | Rules | Impact | When to Use | |----------|-------|--------|-------------| | [Alembic Migrations](#alembic-migrations) | 2 | CRITICAL | Data migrations, branch management | | [Schema Design](#schema-design) | 3 | HIGH | Normalization, indexing strategies, NoSQL patterns | | [Versioning](#versioning) | 2 | HIGH | Changelogs, schema drift detection | | [Zero-Downtime Migration](#zero-downtime-migration) | 2 | CRITICAL | Expand-contract, pgroll, rollback monitoring |

| [Database Selection](#database-selection) | 1 | HIGH | Choosing the right database, PostgreSQL vs MongoDB, cost analysis |

**Total: 10 rules across 5 categories**

This skill is a wrap around Alembic and PostgreSQL, not a replacement for their docs. Read `references/ork-delta.md` first: it holds the version floors, corrections and house conventions that upstream does not carry. Everything in the table below was removed on purpose.

Upstream coverage (do not restate)

These topics are vendor documentation. Fetch them from the source instead of re-teaching them here.

| Topic | First-party source | |-------|--------------------| | Alembic autogenerate, async `env.py` template, `revision`/`upgrade`/`downgrade`/`history` CLI | https://alembic.sqlalchemy.org/en/latest/autogenerate.html (our one correction to the async template is in `references/ork-delta.md`) | | Migration branches, merge revisions, tuple `down_revision`, branch labels | https://alembic.sqlalchemy.org/en/latest/branches.html | | Multi-database `env.py`, batched backfill recipes, migration hooks, environment-conditional migrations | https://alembic.sqlalchemy.org/en/latest/cookbook.html | | Rollback and data-integrity test harnesses | `references/migration-testing.md` | | JSONB operators, indexing and storage tradeoffs | https://www.postgresql.org/docs/current/datatype-json.html (normal forms and the house denormalization call stay in `rules/schema-normalization.md`) | | Full index-type reference and syntax (B-tree, GIN, partial, covering, `CREATE INDEX CONCURRENTLY`, `REINDEX`) | https://www.postgresql.org/docs/current/sql-createindex.html (the house subset we actually apply stays in `rules/schema-indexing.md`) | | `lock_timeout`, `statement_timeout`, advisory locks during migration | https://www.postgresql.org/docs/current/runtime-config-client.html and `rules/versioning-drift.md` | | Enum type changes | https://www.postgresql.org/docs/current/datatype-enum.html | | Table partitioning | https://www.postgresql.org/docs/current/ddl-partitioning.html | | Trigger functions | https://www.postgresql.org/docs/current/plpgsql-trigger.html | | Foreign-key cascade semantics | https://www.postgresql.org/docs/current/ddl-constraints.html | | Temporal and audit-trail tables, CDC change logs, stored-procedure and view versioning | https://www.postgresql.org/docs/18/sql-createtable.html (read `references/ork-delta.md` before assuming these give row history) | | HNSW and vector index tuning (`m`, `ef_construction`, `hnsw.ef_search`) | https://github.com/pgvector/pgvector | | Generic pre-deployment, backup and schema-review checklists | https://alembic.sqlalchemy.org/en/latest/tutorial.html | | Async SQLAlchemy sessions, FastAPI wiring, connection pool tuning | `ork:python-backend` skill |

Quick Start

# Alembic: Auto-generate migration from model changes
# alembic revision --autogenerate -m "add user preferences"

def upgrade() -> None:
    op.add_column('users', sa.Column('org_id', UUID(as_uuid=True), nullable=True))
    op.execute("UPDATE users SET org_id = 'default-org-uuid' WHERE org_id IS NULL")

def downgrade() -> None:
    op.drop_column('users', 'org_id')

-- Schema: Normalization to 3NF with proper indexing
-- PG18: prefer uuidv7() (time-ordered, better B-tree locality) over gen_random_uuid() (random v4)
CREATE TABLE orders (
    id UUID PRIMARY KEY DEFAULT uuidv7(),
    customer_id UUID NOT NULL REFERENCES customers(id),
    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
CREATE INDEX idx_orders_customer_id ON orders(customer_id);

Alembic Migrations

Migration management with Alembic for SQLAlchemy 2.0 async applications.

| Rule | File | Key Pattern | |------|------|-------------| | Data Migration | `rules/alembic-data-migration.md` | Batch backfill, two-phase NOT NULL, zero-downtime | | Branching | `rules/alembic-branching.md` | Feature branches, merge migrations, conflict resolution |

Autogenerate setup is upstream. Our one deviation from Alembic's async `env.py` template (the `in_greenlet()` guard) is in `references/ork-delta.md`.

Schema Design

SQL and NoSQL schema design with normalization, indexing, and constraint patterns.

| Rule | File | Key Pattern | |------|------|-------------| | Normalization | `rules/schema-normalization.md` | 1NF-3NF, when to denormalize, JSON vs no