Accounts, Transactioins and Ledger Implementatioin

Phase 0: Foundations & Tooling

Tech Stack & Infrastructure

PostgreSQL (13+), with plpgsql triggers

Node.js + TypeScript

TypeORM (or Prisma) for ORM + migrations

Flyway or Liquibase as an alternative for DDL versioning

decimal.js for all money fields

Validation & Schema

Zod (or AJV) for JSONB schemas

class-validator + class-transformer for entity‐level checks

Testing & CI

Jest + TestContainers to spin up real Postgres in CI

Supertest for HTTP/integration tests

GitHub Actions (or equivalent) for linting, migrations, tests

Observability & Security

Winston / Pino for structured logs

Sentry for error tracking

Prometheus + Grafana for metrics

Phase 1: Core Account Model

Table	Purpose
`account_types`	Defines “kinds” (e.g. SAVINGS, CHECKING)
`account_balances`	Real-time running balance per account
`account_type_transaction`	Which transaction types each account type is allowed to perform
`accounts`	Actual account record (FK → type, country, currency, status)

Key DB Features:

Unique index on account_types.code

Trigger on ledger_entries to update account_balances

Pessimistic‐locking methods in service to avoid race conditions

Phase 2: Transaction Type Configuration

Table	Purpose
`transaction_types`	Master list (code, description, `requires_two_factor`, JSONB)
`transaction_type_postings`	(Optional) normalized posting templates per transaction type

Key Features:

JSONB or separate table for posting templates

Zod/AJV schema to validate that postings sum to 100% and refer to valid account types

Phase 3: Domain Transactions

Table	Purpose
`domain_transactions`	Business-level record (payer, payee, amount, status, etc.)
`domain_transaction_history`	Audit of status changes, attachments, idempotency keys

Key Features:

Status enum transitions (PENDING → POSTED → FAILED)

FK to transaction_types, optional idempotency_key

Phase 4: Ledger Header & Lines

Table	Purpose
`ledger_transactions`	“Header” linking back to a domain txn, with metadata & reference
`ledger_entries`	Individual debit/credit lines (FK → ledger_transaction, account, side, amount)

Key Features:

Trigger: enforce_double_entry() to ensure Σ(debits) = Σ(credits)

Trigger: adjust_account_balance() to maintain account_balances

Unique or partial‐unique constraints on reference, domain_txn_id

Phase 5: Audit, Idempotency & Outbox

Table	Purpose
`ledger_transaction_history`	Immutable record of every header change
`idempotency_keys`	Global registry of idempotency tokens to prevent duplicates
`outbox_events`	For reliable pub/sub / eventing (e.g. notify downstream)

Phase 6: Service Layer & Orchestration

Atomic “Post Transaction” with TypeORM QueryRunner at SERIALIZABLE

Steps:

Create & validate DomainTransaction

Instantiate LedgerTransaction + LedgerEntry[] via template

Save header (cascades to entries) → triggers fire → balances update

Record in outbox_events if needed

Commit or rollback on any error (unbalanced, constraint, validation)

Repository Methods for:

Fetching balances with FOR UPDATE lock

Searching transactions by date/account/status

Phase 7: Validation, Testing & CI

Unit Tests: JSONB schemas, service error paths

Integration Tests:

Triggers (unbalanced entries must fail)

Concurrency (two debits at once update account_balances correctly)

CI Pipeline: lint → build → migrations → tests

Phase 8: Security & Hardening

DB roles & permissions (readonly vs write)

Audit logging at service layer

2FA enforcement for high-risk transaction types

Phase 9: Scaling & Partitioning

Partition ledger_entries by date (e.g. monthly) for very large volumes

Archival process to move old partitions to cheaper storage

Phase 10: Monitoring & Maintenance

Regular drift checks (Flyway)

Health checks on balances vs trial-balance reports

Alerts if any trigger failures or balance mismatches

All Tables at a Glance

account_types
account_balances
account_type_transaction
accounts

transaction_types
transaction_type_postings

domain_transactions
domain_transaction_history

ledger_transactions
ledger_entries
ledger_transaction_history
idempotency_keys
outbox_events

➡️ Next: Phase 1, implement account_types + its migration, entity, indexes, metadata schema, and triggers for balance adjustments. Shall we dive into that?

Accounts, Transactioins and Ledger Implementatioin

Phase 0: Foundations & Tooling#

Phase 1: Core Account Model#

Phase 2: Transaction Type Configuration#

Phase 3: Domain Transactions#

Phase 4: Ledger Header & Lines#

Phase 5: Audit, Idempotency & Outbox#

Phase 6: Service Layer & Orchestration#

Phase 7: Validation, Testing & CI#

Phase 8: Security & Hardening#

Phase 9: Scaling & Partitioning#

Phase 10: Monitoring & Maintenance#

Phase 0: Foundations & Tooling

Phase 1: Core Account Model

Phase 2: Transaction Type Configuration

Phase 3: Domain Transactions

Phase 4: Ledger Header & Lines

Phase 5: Audit, Idempotency & Outbox

Phase 6: Service Layer & Orchestration

Phase 7: Validation, Testing & CI

Phase 8: Security & Hardening

Phase 9: Scaling & Partitioning

Phase 10: Monitoring & Maintenance