Question

我对ruby很新，我正在尝试使用连接方法来获取属于我的表演的表演者。使用这个简单的代码（在我的头标记内）：

window.performances = <%=raw Performance.joins(:performers).to_json(:include => {:performers =>  {
                                                                                        :except => [ :created_at, :updated_at ]
                                                                                        }}, :except => [ :created_at, :updated_at ]) %> ;
alert(JSON.stringify(window.performances));

这很好用，除了我得到所有表演的输出两次而不是一次。像这样：

[{"id":1,"date":"2011-12-10","location":"Malgorzaty i Zygmunta Belza","performers":[{"id":1,"name":"Wojtek Szewczuk"},{"id":2,"name":"Danuta Sroka"}]},{"id":1,"date":"2011-12-10","location":"Malgorzaty i Zygmunta Belza","performers":[{"id":1,"name":"Wojtek Szewczuk"},{"id":2,"name":"Danuta Sroka"}]},{"id":2,"date":"2011-12-10","location":"Malgorzaty i Zygmunta Belza","performers":[{"id":1,"name":"Wojtek Szewczuk"},{"id":2,"name":"Danuta Sroka"}]},{"id":2,"date":"2011-12-10","location":"Malgorzaty i Zygmunta Belza","performers":[{"id":1,"name":"Wojtek Szewczuk"},{"id":2,"name":"Danuta Sroka"}]}, ...

我假设它与存在的执行者数量有关，因此每个执行者都会从数据库中生成新结果。我只是不明白为什么会这样？

我做错了什么，如何避免我的结果中的重复。

Answer 1

因为 joins 创建 duplicate values 。您使用 includes 来摆脱重复值。

window.performances = <%=raw Performance.includes(:performers).to_json(:include => {:performers =>  {
                                                                                        :except => [ :created_at, :updated_at ]
                                                                                        }}, :except => [ :created_at, :updated_at ]) %> ;
alert(JSON.stringify(window.performances));

includes 还可以避免 N+1 生成 DB 。

请参阅以下 Guides 了解更多信息。我希望它有所帮助！

连接重复结果

1 个答案: