django.db.utils.OperationalError: FATAL: database “library” does not exist

Question

I'm trying to connect my project with postgres database using docker.It works fine when I use default postgres setup like

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'postgres',
        'USER': 'postgres',
        'PASSWORD': 'postgres',
        'HOST': 'db',
        'PORT': 5432
    }
}

but when i try to create a database using postgre admin and want to use it in my django project it shows the error. my Dockerfile:

Dockerfile
# Pull base image
FROM python:3.7
# Set environment variables
ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONUNBUFFERED 1
# Set work directory
WORKDIR /code
# Install dependencies
COPY Pipfile Pipfile.lock /code/
RUN pip install pipenv && pipenv install --system
# Copy project
COPY . /code/

the settings.py for databse

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'library',
        'USER': 'postgres',
        'PASSWORD': 'my_password',
        'HOST': 'db',
        'PORT': 5432
    }
}

and the docker-compose.yml

docker-compose.yml
version: '3.7'
    
services:
  db:
    hostname: db
    image: postgres:11
    environment:
      - POSTGRES_DB=library
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=my_password
    volumes:
      - postgres_data:/var/lib/postgresql/data
    ports:
      - "5432:5432"
  web:
    build: .
    command: python manage.py runserver 0.0.0.0:8000
    volumes:
      - .:/code
    ports:
      - "8000:8000"
    depends_on:
      - db
volumes:
  postgres_data:

Answer 1

When the postgres image is first started and has no data it will create a database with the name of the POSTGRES_DB environment variable.

You already have a database created in your volume. You should delete your postgres_data volume and restart so that a database with the new name is created. Pass -v to docker-compose down to delete any volumes

docker-compose down -v
docker-compose up -d