Entity modelling

What it is

Entities have stable identity through changing attributes.

When to use it

Separate persistent entities from value objects and DTOs.

Syntax

User 1 -> many Accounts
Account 1 -> many Transactions

Example

User: id, email
Account: id, user_id, currency
Transaction: id, account_id, amount_cents, status, external_reference
Money value: amount_cents + currency

Common mistakes

Do not use mutable email as an entity ID; distinguish an account from its balance value.

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