活动记录：语句无效。PG 错误

Question

我正在尝试使用Project.find(id)从Project模型中查找一个项目，但是它给出了一个ActiveRecord :: StatementInvalid错误。

完整跟踪信息-

 PG::Error: ERROR: prepared statement "a1" already exists : SELECT COUNT(*) FROM pg_class c LEFT JOIN pg_namespace n ON n.oid = c.relnamespace WHERE c.relkind in ('v','r') AND c.relname = $1 AND n.nspname = ANY (current_schemas(false))
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/connection_adapters/postgresql_adapter.rb:1180:in `prepare'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/connection_adapters/postgresql_adapter.rb:1180:in `prepare_statement'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/connection_adapters/postgresql_adapter.rb:1144:in `exec_cache'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-     3.2.2/lib/active_record/connection_adapters/postgresql_adapter.rb:664:in `block in exec_query'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/connection_adapters/abstract_adapter.rb:280:in `block in log'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activesupport-3.2.2/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/connection_adapters/abstract_adapter.rb:275:in `log'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/connection_adapters/postgresql_adapter.rb:662:in `exec_query'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/connection_adapters/postgresql_adapter.rb:797:in `table_exists?'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/connection_adapters/schema_cache.rb:30:in `table_exists?'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/model_schema.rb:223:in `table_exists?'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/attribute_methods/primary_key.rb:75:in `get_primary_key'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/attribute_methods/primary_key.rb:60:in `reset_primary_key'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/attribute_methods/primary_key.rb:49:in `primary_key'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/model_schema.rb:230:in `block in columns'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/model_schema.rb:228:in `map'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/model_schema.rb:228:in `columns'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/model_schema.rb:237:in `columns_hash'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/relation/delegation.rb:7:in `columns_hash'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/relation/finder_methods.rb:330:in `find_one'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/relation/finder_methods.rb:311:in `find_with_ids'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/relation/finder_methods.rb:107:in `find'
/home/deploy/.rvm/gems/ruby-1.9.2-p290@submit_contactpl/gems/activerecord-3.2.2/lib/active_record/querying.rb:5:in `find'
/home/deploy/submit_contactpl/app/workers/php_worker.rb:5:in `perform'

php_worker 的第5行是：

 project = Project.find(project_id)

可能出了什么问题？你能为此指明一些线索吗？有什么可能的解决方案吗？

- Bhushan Lodha

Answer 1

所有它需要的只是

 task "resque:setup" => :environment do
  #ENV['QUEUE'] = '*'

  Resque.before_fork = Proc.new { ActiveRecord::Base.establish_connection }
 end

在你的 resque.rake 文件中

- Bhushan Lodha

---

这个应该放在config/initializers/resque.rb里面，这样每次resque分叉时它都是活动的，不是吗？ - radiospiel

这到底是在做什么？为什么我们必须这样做？这个问题在Resque或Rails的未来版本中是否已经修复了（无论这个bug存在于哪里）？ - user3827303

Answer 2

您的 Ruby 堆栈中可能存在一个 bug。

它试图准备一个名为 "a1" 的语句，该语句正在检查表/视图定义（可能是针对您的“项目”表）。它发现已经存在相同名称的预处理语句，并抛出错误。它试图准备的查询是正确的 - 它返回具有给定名称的表格数。

要么它没有正确跟踪其预处理语句，要么它认为已经删除了一个但实际上并没有。我建议更新 Rails 和 ActiveRecord 并检查是否有 bug 报告。

- Richard Huxton