Can't to connect to postgres container

I define postgres server in docker-compose.yml:

db:
    image: postgres:9.5
    expose:
        - 5432

Then in another docker container I tried to connect to this postgres container. But it gives an error with warning:

Is the server running on host "db" (172.22.0.2) and accepting
data-service_1  |   TCP/IP connections on port 5432?

Why container can't to connect to another by provided information (host="db" and port=5432)?

PS Full docker-compose.yml:

version: "2"
services:
    data-service:
        build: .
        depends_on:
            - db
        ports:
          - "50051:50051"
    db:
        image: postgres:9.5
        depends_on:
            - data-volume
        environment:
            - POSTGRES_USER=cobrain
            - POSTGRES_PASSWORD=a
            - POSTGRES_DB=datasets
        ports:
          - "8000:5432"
        expose:
            - 5432
        volumes_from:
            - data-volume
            # - container:postgres9.5-data
        restart: always

    data-volume:
        image: busybox
        command: echo "I'm data container"
        volumes:
            - /var/lib/postgresql/data