Data Layer

Goal

This snapshot advances Baltic Post by teaching you to persist authors and posts with Exposed and PostgreSQL.

Every numbered folder is a complete app. Run this stage independently, then compare it with the previous folder.

Prerequisites

Use JDK 17+, Gradle, and Docker for Postgres stages.

Port 8090 must be free. Copy .env.example before starting database stages.

• JDK 17+ and Gradle
• A code editor and terminal
• Docker from part 4 onward

Concepts

Exposed table objects map schema. Each snapshot uses its own baltic database.

Keep handlers thin: routes accept input, Exposed tables enforce rules, and FreeMarker escapes output by default.

Walkthrough

Connect DATABASE_URL, create Users and Posts tables, seed Ada and Grace.

Read the example, then open the matching snapshot. The repository includes the surrounding setup and error handling.

Posts.selectAll().orderBy(Posts.createdAt to SortOrder.DESC).map { ... }

Run and verify

Enter 04-Data-Layer, run Gradle, copy .env.example, and start Ktor on port 8090.

Open http://127.0.0.1:8090. Watch the terminal for validation and database errors.

docker compose up -d
git clone https://github.com/michaeldunga1/fcc-ktor-blog.git
cd fcc-ktor-blog/04-Data-Layer
cp .env.example .env
./gradlew run

Troubleshooting

Connection refused usually means Docker Postgres is stopped or the port is not 5439.

For database failures, confirm Docker and the baltic_NN name when applicable. Never commit .env or local.properties secrets.

• Read the first error first
• Restart after environment changes
• Never commit secrets

Try this

Add a minimum title length check before insert.

Test a happy path and one invalid or unauthorized request.

• Make one small change
• Test it in the browser
• Compare with the next snapshot only after it works