DEVELOPER_NOTES.md

Developer Notes - Relational Data Access

Personal notes and detailed explanations for the spring-relational-data-access module.

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Phase 1: Spring Guide Implementation

Following the official Spring Guide with H2 in-memory database.

Index

Section	File	Description
Customer.java	Source	Domain model for customer data
RelationalDataAccessApplication.java	Source	Main app with CommandLineRunner

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Customer.java

Path: src/main/java/com/example/relationaldataaccess/Customer.java

Purpose

{What does this class do? Simple POJO to hold customer data from the database}

Key Concepts

• Plain Java object (no annotations needed for JDBC)
• Maps to database table columns

My Notes

{Personal observations, things you learned}

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RelationalDataAccessApplication.java

Path: src/main/java/com/example/relationaldataaccess/RelationalDataAccessApplication.java

Purpose

{Main application that demonstrates JdbcTemplate usage}

Key Annotations

Annotation	Purpose
@SpringBootApplication	{What it does}

JdbcTemplate Methods Used

Method	Purpose
execute()	{DDL statements like CREATE TABLE}
batchUpdate()	{Insert multiple records}
query()	{Select with RowMapper}

My Notes

{Personal observations about JdbcTemplate, gotchas encountered}

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Phase 1 Testing Notes

What's Tested

Test	Verifies
contextLoads()	{Application context starts}

Test Patterns Used

• {Pattern}: {Why we use it}

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Phase 1 Questions Answered

Q: {Question you had while learning}

A: {Answer you discovered}

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Phase 2: My Enhancements

Extending beyond the guide with PostgreSQL and custom additions.

What Changed

Change	Why	ADR
H2 -> PostgreSQL	{Production-ready DB, learning real setup}	ADR-0001
{Other enhancement}	{Reason}	ADR-XXXX

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PostgreSQL Setup

Local Development

# Docker command used
docker run -d -p 5432:5432 -e POSTGRES_PASSWORD=pass postgres:16

Configuration Changes

# application.properties changes
spring.datasource.url=jdbc:postgresql://localhost:5432/yourdb
spring.datasource.username=user
spring.datasource.password=pass

My Notes

{What was different from H2? Gotchas?}

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CI/CD Changes

GitHub Actions Service Container

{Notes on how Postgres runs in CI}

My Notes

{What I learned about service containers}

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Additional Enhancements

{Enhancement 1}

{What you added, why, what you learned}

{Enhancement 2}

{What you added, why, what you learned}

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Phase 2 Testing Notes

New Tests Added

Test	Verifies
{test name}	{what it tests}

Integration Testing with Postgres

{Notes on testing against real DB vs H2}

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Phase 2 Questions Answered

Q: {Question you had}

A: {Answer you discovered}

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TODOs

• Complete Phase 1 implementation
• Run ./mvnw clean verify
• Commit Phase 1
• Add PostgreSQL dependency
• Update CI workflow
• Write ADR-0001 for Postgres switch

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References

• Spring Guide: Relational Data Access
• Spring Docs: JdbcTemplate
• PostgreSQL Docker Image
• GitHub Actions Service Containers