Data Integrity Patterns

Maintaining data correctness through database constraints and patterns.

Context

You are ensuring data stays correct. Use database constraints, not just application validation.

Domain Context

• Constraints: NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK
• Triggers: Automatic actions on data changes; use sparingly
• Audit Trail: Record of what changed and when
• Referential Integrity: Foreign keys prevent orphaned records
• Validation: Business rules enforced at database level

Instructions

1. NOT NULL: Columns that must have values
2. UNIQUE: Columns/combinations that must be unique
3. FOREIGN KEYS: References to other tables; prevent orphans
4. CHECK: Business rules (price > 0, status IN (values))
5. Triggers: Rarely; keep business logic in application
6. Audit Trail: Timestamp, user columns; or trigger for history table
7. Enforcement: Database enforces; application can't bypass

Anti-Patterns

• No constraints; trust application to validate (it won't)
• Over-reliance on triggers; hard to test, understand
• Audit table with triggers; complex and slow
• CHECK constraints that are wrong; don't trust them until tested
• Not testing constraint enforcement

Further Reading

• PostgreSQL constraints documentation
• Data Vault 2.0 (for audit trail patterns)
• Event sourcing for audit trails (alternative)