how i can connect to postgres in docker containers in code example

Example: postgresql not connected docker

# you must use port 5432 for host, if you use another port, database cannot connected

DATABASE_URI=postgres://<your username>:<your password>@postgresql:5432/db_name

services  
  postgresql:
    container_name: postgresql
    image: postgres
    ports: 
      - '5432:5432'