create a new Database in Ruby

Create a Docker network:

This is something docker compose will set up for us; this network allows containers to communicate with each other.

docker network create myapp-network

Run PostgreSQL container:

docker run --name postgres \
  -e POSTGRES_PASSWORD=mysecretpassword \
  --network myapp-network \
  -d postgres

• --name postgres: Names the container for easy reference.
• -e POSTGRES_PASSWORD=mysecretpassword: Sets the database password.
• --network myapp-network: Connects to the created network.
• -d: Runs in detached mode.

Test a Database operation

run the rails/backend container:

cd backend/
docker build -t backend -f Dockerfile.dev .
docker run --rm \
  --network myapp-network \
  -e DATABASE_URL=postgres://postgres:mysecretpassword@postgres:5432/myapp_development \
  backend rails db:create

• --rm: Removes the container after execution.
• --network myapp-network: Connects to the same network as PostgreSQL.
• -e DATABASE_URL=...: Sets the database connection string.
  • postgres://: Specifies the database type.
  • postgres:mysecretpassword: Username and password.
  • @postgres: Hostname (container name of PostgreSQL).
  • :5432: Default PostgreSQL port.
  • /myapp_development: Database name. rails db create command

If successful, you should see a message like “Created database ‘app_development’“.

Test again:

curl http://localhost:3001

You should now see valid output! Database created!

If you still encounter issues, check your config/database.yml file to ensure it’s properly configured for your Docker environment.