postgresql - Rails 5 - PG::UndefinedTable: 错误:关系 "application_records"不存在

Question

我正在尝试使用 postgresql、devise gems 设置一个新 Rails 5 应用程序(ruby 2.3.1、rails 5.0.0.rc1)，但它无法运行rails db:seed 由于以下错误:

PG::UndefinedTable: ERROR:  relation "application_records" does not exist
LINE 8:                WHERE a.attrelid = '"application_records"'::r...
                                          ^
/Users//.rvm/gems/ruby-2.3.1@rails5.0/gems/activerecord-5.0.0.rc1/lib/active_record/connection_adapters/postgresql/database_statements.rb:88:in `async_exec'
/Users/foo/.rvm/gems/ruby-2.3.1@rails5.0/gems/activerecord-5.0.0.rc1/lib/active_record/connection_adapters/postgresql/database_statements.rb:88:in `block in query'
/Users/foo/.rvm/gems/ruby-2.3.1@rails5.0/gems/activerecord-5.0.0.rc1/lib/active_record/connection_adapters/abstract_adapter.rb:566:in `block in log'
/Users/foo/.rvm/gems/ruby-2.3.1@rails5.0/gems/activesupport-5.0.0.rc1/lib/active_support/notifications/instrumenter.rb:21:in `instrument'
/Users/foo/.rvm/gems/ruby-2.3.1@rails5.0/gems/activerecord-5.0.0.rc1/lib/active_record/connection_adapters/abstract_adapter.rb:560:in `log'
/Users/foo/.rvm/gems/ruby-2.3.1@rails5.0/gems/activerecord-5.0.0.rc1/lib/active_record/connection_adapters/postgresql/database_statements.rb:87:in `query'
/Users/foo/.rvm/gems/ruby-2.3.1@rails5.0/gems/activerecord-5.0.0.rc1/lib/active_record/connection_adapters/postgresql_adapter.rb:739:in `column_definitions'
/Users/foo/.rvm/gems/ruby-2.3.1@rails5.0/gems/activerecord-5.0.0.rc1/lib/active_record/connection_adapters/postgresql/schema_statements.rb:227:in `columns' 

经过多次谷歌搜索，我意识到这与 ApplicationRecord base class change in rails 5 有关.显然没有名为 application_records 的表，因此 active_support 不应该寻找它。我已经检查过 app/models/application_record.rb 存在并且内容正确。此外，用户模型(这是我的应用程序中目前唯一的模型)按预期扩展了 ApplicationRecord:

class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, 
         :recoverable, :rememberable, :trackable, :validatable
end

rails db: migrate 运行正常，但 rails db:seed 因上述错误而阻塞。

任何人都可以阐明可能导致这种情况的原因吗？

application_record.rb 的内容:

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
end

Answer 1

PG::UndefinedTable: ERROR:  relation "application_records" does not exist

如果删除该行，也会发生错误:

self.abstract_class = true

来自 app/models/application_record.rb

该行让 Rails 知道这不是一个应该持久保存到数据库的模型，这里有 Rails 抽象类的一个很好的总结:https://medium.com/@jeremy_96642/deep-rails-how-to-use-abstract-classes-6aee9b686e75