执行多个联接与Squeel同一协会 [英] Performing multiple joins on the same association with Squeel

问题描述

在我的申请，我要的型号：工作流程和步骤;步骤 belongs_to的工作流和工作流的has_many 步骤。步骤有一个索引和一个布尔状态（'完成'）。
我想要检索的工作流，其完成步骤1和步骤2没有的，即像这样在SQL：

In my application, I have to models: Workflow and Step; steps belongs_to workflow and a workflow has_many steps. Steps have an index and a boolean status ('completed'). I want to retrieve workflows whose step 1 is completed and step 2 is not, i.e. something like this in SQL:

SELECT * FROM workflows w
INNER JOIN steps s1 ON s1.workflow_id = w.id
INNER JOIN steps s2 ON s2.workflow_id = w.id
WHERE s1.index = 1 AND s1.completed = 1
AND s2.index = 2 AND s2.completed = 0

我试过前preSS此查询与Squeel，但似乎它不允许在同一个协会的多个联接：我无法找到一个方法来命名的连接，当我输入这样的事情： Workflow.joins {步} {.joins步骤} ，生成的SQL很简单：

I've tried to express this query with Squeel, but it seems it does not allow multiple joins on the same association: I cannot find a way to name the joins, and when I type something like this: Workflow.joins{steps}.joins{steps}, the generated SQL is simply:

SELECT `workflows`.* FROM `workflows` 
INNER JOIN `workflow_steps` ON `workflow_steps`.`workflow_id` = `workflows`.`id`

任何想法，我怎么能做到这一点？

Any idea how I can achieve that?

推荐答案

我不知道你会喜欢它，但它通过自我参照是可能的：

I don't know if you gonna like it, but it's possible via self-reference:

Workflow.joins{steps.workfolw.steps}.
  where{(steps.index == 1) & (steps.completed == true)} &
        (steps.workfolw.steps.index == 2) & (steps.workfolw.steps.completed == false)}.
  uniq

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