GoLang服务无法使用docker compose访问Postgres

version: '3'
services:
  app:
    build: .
    networks:
      - mynetwork
  db:
    image: postgres
    networks:
      - mynetwork

networks:
  mynetwork:

version: '3'
services:
  app:
    build: .
    ports:
      - 8080:8080
    networks:
      - mynetwork
  db:
    image: postgres
    networks:
      - mynetwork

networks:
  mynetwork:

import (
    "database/sql"
    _ "github.com/lib/pq"
)

func main() {
    db, err := sql.Open("postgres", "host=db user=postgres password=yourpassword dbname=yourdbname sslmode=disable")
    if err != nil {
        panic(err)
    }
    defer db.Close()

    // 进行数据库操作...
}

version: '3'
services:
  app:
    build: .
    ports:
      - 8080:8080
    networks:
      - mynetwork
    depends_on:
      - db
  db:
    image: postgres
    networks:
      - mynetwork

networks:
  mynetwork: