我有一个Rails 5 docker-compose项目(Github link)，可以在多个容器中正常工作。
我可以使用docker-compose exec app rails db:create创建数据库，并在localhost:3000上运行项目
问题在于它总是错误：
could not connect to server: No such file or directory成功完成命令后。
当我要使用执行其他3个命令的db:setup时，这是一个问题。它先完成第一个命令，然后执行错误，提示连接断开，无法执行其余2个命令。
是否关闭了命令之间的连接？我该如何进一步调试呢？
Rails 5.2.1，第1.1.3页Gemfile
RAILS_ENV在.env文件中定义。在这种情况下是：
root@3ec00f6534aa:/app# printenv|grep RAILS
RAILS_ENV=development
这是执行docker-compose exec app bash后从应用程序容器内输出的错误。
注意第二行，说数据库已创建：
root@b281e881b96a:/app# rake db:setup
Created database 'sc_dev'
could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
Couldn't create database for {"adapter"=>"postgresql", "encoding"=>"unicode", "pool"=>10, "database"=>"smartcitizen_testing"}
rake aborted!
PG::ConnectionBad: could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
/usr/local/bundle/gems/pg-1.1.3/lib/pg.rb:56:in `initialize'
/usr/local/bundle/gems/pg-1.1.3/lib/pg.rb:56:in `new'
/usr/local/bundle/gems/pg-1.1.3/lib/pg.rb:56:in `connect'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/postgresql_adapter.rb:684:in `connect'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/postgresql_adapter.rb:215:in `initialize'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/postgresql_adapter.rb:40:in `new'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/postgresql_adapter.rb:40:in `postgresql_connection'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:809:in `new_connection'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:853:in `checkout_new_connection'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:832:in `try_to_checkout_new_connection'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:793:in `acquire_connection'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:521:in `checkout'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:380:in `connection'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:1008:in `retrieve_connection'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_handling.rb:118:in `retrieve_connection'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/connection_handling.rb:90:in `connection'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/tasks/postgresql_database_tasks.rb:12:in `connection'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/tasks/postgresql_database_tasks.rb:21:in `create'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/tasks/database_tasks.rb:119:in `create'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/tasks/database_tasks.rb:139:in `block in create_current'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/tasks/database_tasks.rb:316:in `block in each_current_configuration'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/tasks/database_tasks.rb:313:in `each'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/tasks/database_tasks.rb:313:in `each_current_configuration'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/tasks/database_tasks.rb:138:in `create_current'
/usr/local/bundle/gems/activerecord-5.2.1/lib/active_record/railties/databases.rake:29:in `block (2 levels) in <main>'
/usr/local/bundle/gems/rake-12.3.1/exe/rake:27:in `<top (required)>'
Tasks: TOP => db:setup => db:schema:load_if_ruby => db:create
(See full trace by running task with --trace)
答案 0 :(得分：1)
您正在运行rails db:create，但未指定环境。因此，Rails会努力为您节省一些精力，并在开发和测试环境中都运行该命令（我不记得它们以什么顺序运行）。您会看到sc_dev数据库已创建，但是错误提示它无法为smartcitizen_testing数据库创建数据库。
Rails可以连接到您的开发数据库，但不能连接到测试数据库。
经过反复评论，我了解到您正在使用DATABASE_URL环境变量，这是有问题的，因为测试数据库和开发数据库实际上并不共享相同的数据库URL。解决方案是修改database.yml，以便可以通过环境变量独立配置开发和测试数据库，从而允许它们在运行单个rails db:create命令时各自具有自己的设置。