07. Design data model

What it is

Choose primary/foreign keys, nullability, uniqueness, indexes, retention, and amounts.

When to use it

Workflow step 7 of 17. Apply before moving to the next decision.

Syntax

7. Design data model
Choose primary/foreign keys, nullability, uniqueness, indexes, retention, and amounts.

Example

accounts: id PK, user_id FK, currency, balance_cents.
transactions: id PK, account_id FK, reference UNIQUE, state.
Index transactions(account_id, id).

Common mistakes

Skipping this decision makes later implementation depend on unstated assumptions.

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