ActiveRecord Postgres适配器生成无效的SQL WHERE子句：WHERE（“ fieldname”）

Question

ActiveRecord 4.1.1在保存时生成了一些奇怪的SQL，而这些都是postgres遇到的：

SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
PG::InvalidTextRepresentation: ERROR:  invalid input syntax for type boolean: "uid"

我很确定这里引用的“布尔值”实际上是WHERE()语法，它期望布尔表达式作为参数。

uid被定义为模型的主键（请参见下文）...但是为什么在执行select_all时仅说WHERE('uid') （请参见stacktrace）？ （为什么它在保存时执行select_all？）

Rails控制台

p = Project.new(name: "test", description: "test", workflow_id: 1)
=> #<Project name: "test", description: "test", user_id: nil, uid: nil, created_at: nil, updated_at: nil, workflow_id: 1, active: nil>
irb(main):031:0> p.save
   (1.9ms)  BEGIN
  Project Load (5.5ms)  SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
PG::InvalidTextRepresentation: ERROR:  invalid input syntax for type boolean: "uid"
LINE 1: SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
                                                     ^
: SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
   (1.7ms)  ROLLBACK
ActiveRecord::StatementInvalid: PG::InvalidTextRepresentation: ERROR:  invalid input syntax for type boolean: "uid"
LINE 1: SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
                                                     ^
: SELECT  "projects".* FROM "projects"  WHERE ('uid') LIMIT 1
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:815:in `async_exec'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:815:in `block in exec_no_cache'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract_adapter.rb:373:in `block in log'
    from /app/vendor/bundle/ruby/2.0.0/gems/activesupport-4.1.1/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract_adapter.rb:367:in `log'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:815:in `exec_no_cache'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/postgresql/database_statements.rb:137:in `exec_query'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:947:in `select'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/database_statements.rb:31:in `select_all'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/query_cache.rb:69:in `select_all'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/querying.rb:39:in `find_by_sql'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/relation.rb:603:in `exec_queries'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/relation.rb:487:in `load'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/relation.rb:231:in `to_a'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/relation/finder_methods.rb:451:in `find_take'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/relation/finder_methods.rb:98:in `take'
... 41 levels...
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/database_statements.rb:211:in `block in transaction'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/database_statements.rb:219:in `within_new_transaction'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/abstract/database_statements.rb:211:in `transaction'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/transactions.rb:208:in `transaction'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/transactions.rb:326:in `with_transaction_returning_status'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/transactions.rb:268:in `block in save'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/transactions.rb:283:in `rollback_active_record_state!'
    from /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.1.1/lib/active_record/transactions.rb:267:in `save'
    from (irb):31
    from /app/vendor/bundle/ruby/2.0.0/gems/railties-4.1.1/lib/rails/commands/console.rb:90:in `start'
    from /app/vendor/bundle/ruby/2.0.0/gems/railties-4.1.1/lib/rails/commands/console.rb:9:in `start'
    from /app/vendor/bundle/ruby/2.0.0/gems/railties-4.1.1/lib/rails/commands/commands_tasks.rb:69:in `console'
    from /app/vendor/bundle/ruby/2.0.0/gems/railties-4.1.1/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
    from /app/vendor/bundle/ruby/2.0.0/gems/railties-4.1.1/lib/rails/commands.rb:17:in `<top (required)>'
    from /app/bin/rails:4:in `require'
    from /app/bin/rails:4:in `<main>

模型

class Project < ActiveRecord::Base

  self.primary_key = "uid"

end

ActiveRecord混合生成ID

module ActiveRecordUIDExtension
  extend ActiveSupport::Concern

    def generate_uid
      return unless self.class.column_names.include?("uid")
      self.id = SecureRandom.random_number(36**10).to_s(36)
      while !self.class.find_by(:uid, self.id).nil? do
       self.id = SecureRandom.random_number(36**10).to_s(36)
      end
  end
end

ActiveRecord::Base.send(:include, ActiveRecordUIDExtension)
ActiveRecord::Base.send(:before_create, :generate_uid)

Gemfile.lock

activerecord (4.1.1)
  activemodel (= 4.1.1)
  activesupport (= 4.1.1)
  arel (~> 5.0.0)

Answer 1

您的mixin没有任何意义。 这部分正在导致错误的SQL：

self.class.find_by(:uid, self.id)

产生无效的SQL是因为您要告诉它。 find_by具有灵活的接口，因此必须进行一些解析才能查看您如何调用它。 当你说：

find_by(a, b)

参数解析可能假设您正在尝试使用以下形式：

find_by('some_sql_snippet', placeholder_valid)

如本例中的文档所示：

find_by("published_at < ?", 2.weeks.ago)

然后，它可能会to_s的第一个参数和扫描其中的占位符。 当你说：

find_by(:uid, self.id)

您将最终得到:uid.to_s并且self.id将被忽略，因为该字符串中没有占位符。 这就可以解释为什么您会在SQL中看到where ('uid') 。

修复mixin使其有意义：

self.class.find_by(:uid => self.id)

还是更好，切换到exists? 为了避免仅查看数据库中是否存在一行而构建整个模型实例：

self.class.where(:uid => self.id).exists?
self.class.exists?(:uid => self.id)