I already found some threads to this topic but none of them were able to help me, because I already did the provided solution or the problem was not exactly the same as mine

I have a docker environment with an nginx/php-fpm etc server and am using the official mysql image which I'm linking into the other server. This is my docker-compose

db:
    image: mysql
    ports:
    - "3306:3306"
    environment:
      - MYSQL_ROOT_PASSWORD=symfonyrootpass
      - MYSQL_DATABASE=symfony
      - MYSQL_USER=symfony
      - MYSQL_PASSWORD=symfonypass

project:
    image: docker.io/project/project-dev
    ports:
    - "80:80"
    environment:
      - XDEBUG_HOST=${LOCAL_IP}
      - XDEBUG_PORT=9000
      - XDEBUG_REMOTE_MODE=req
    links:
    - db
    volumes:
    - ../project:/var/www/app

When I start it and connect from my host machine like this: mysql -h127.0.0.1 -usymfony -psymfonypass and then use use symfony; it works without problems. I see my database, I can edit, delete, update etc. I can do everything.

However, I can't say the same for docker. I'm using Symfony and when I have the parameters set correctly, I'm always getting the error

An exception occured in driver: SQLSTATE[HY000] [2002] Connection refused

These are my parameters

database_host: 127.0.0.1
database_port: null
database_name: symfony
database_user: symfony
database_password: symfonypass

I already tried to change database_host to localhost but then I got the error No such file or directory with the same SQLSTATE. I also tried to set the port to 3306 but this also didn't help.

What do I need to do to access my database from inside docker?

This is the part in the config.yml where I describe my mysql connection

Doctrine Configuration

doctrine:
    dbal:
        driver:   pdo_mysql
        host:     "%database_host%"
        port:     "%database_port%"
        dbname:   "%database_name%"
        user:     "%database_user%"
        password: "%database_password%"
        charset:  UTF8
        server_version: "%database_version%"