Rails 中的关联模型和 SUM 查询
我有两个 Rails 模型，一个 Child 和一个 Parent 。
我知道我可以做到这一点：
Child.sum(:income, :conditions => "parent_id = #{@parent_id}")
但我希望能够做到这一点：
Parent.children.sum(:income)
但是如果我尝试的话，这会给我错误的价值观。有没有更简洁的写法
Child.sum(:income, :conditions => "parent_id = #{@parent_id}")
？
TIA
【ps：Rails 3开发环境】
I've got two Rails models, a Child and a Parent say.
I know that I can do this:
Child.sum(:income, :conditions => "parent_id = #{@parent_id}")
But I want to be able to do this:
Parent.children.sum(:income)
But this is giving me the wrong values if I try it. Is there a more concise way of writing
Child.sum(:income, :conditions => "parent_id = #{@parent_id}")
?
TIA
[ps: Rails 3 dev environment]
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抱歉，我刚刚找到了这个问题的答案。我需要将 to_a 添加到 Child 对象的集合中，并调用一个 proc，如下所示：
这很有魅力。
Sorry but I have just found out the answer to this. I needed to add to_a to the collection of Child objects, and call a proc, as so:
This works a charm.
很抱歉撞到旧线程，但我想我找到了更好（最好？）的解决方案。下面是我最终完成的项目的代码
，它生成一个完全符合我需要的查询
Sorry for bumping up an old thread, but I think I found better(best?) solution. Below is code for my project that I ended up
It produces one query that does exactly what I need
我遇到了一个问题，孩子委托给父母，我需要找到一笔金额。
给我带来了一个重大的 N+1 问题。解决方案是使用：
I ran into an issue where the child was delegating to the parent and I needed to find a sum.
was giving me a major N+1 problem. The solution was to use: