试图打造轨道3的范围进行了HABTM关系 [英] Trying to create a scope in rails 3 for has habtm relationship

问题描述

我试图做一个有效记录的一个基本的搜索，但我有因为has_and_belongs_to_many关系的麻烦。下面是记录和范围，我创建的。

I'm trying to do a basic search on an active record but am having trouble because of the has_and_belongs_to_many relationship. Below are the records and scopes I've created.

Class Section << ActiveRecord::Base
  has_and_belongs_to_many :teachers
  attr_accessible :department, :class_size

  scope :department_scope, lambda { |dept| where("department = ?", dept) }
  scope :teacher_fname_scope, lambda { |n| joins(:teachers) & Teacher.has_first_name(n) }
end


Class Teacher << ActiveRecord::Base
  has_and_belongs_to_many :sections
  attr_accessible :first_name, :last_name

  scope :has_first_name, lambda { |fname| where("first_name = ?", fname) }
end

在Rails 3.2我创建一个基本的搜索我的部分型号。假设我想做一个搜索所有部分与给定first_name的一个老师。

In Rails 3.2 I'm creating a basic search for my Sections model. Suppose I want to do a search for all Sections with a Teacher with a given first_name.

我已经试过了使用上述范围，但所有我从* Section.teacher_fname_scope *取回是一个空数组。

I've tried it using the scopes above, but all I'm getting back from *Section.teacher_fname_scope* is an empty array.

（实际上，我有多个字段，让用户也搜索类似部门和class_size科领域，所以我可能会创建多个范围，并最终把它们结合在一起，比如通过同时上面的搜索受限于部门和class_size，但我的理解是这两个范围正交所以这并不重要的问题上面。）

(I'm actually going to have multiple fields, to let the user also search on Section fields like department and class_size so I'll probably create multiple scopes and ultimately chain them together, e.g. the above search by also limited by department and class_size, but my understanding is the scopes are orthogonal so this won't matter to the question above.)

感谢您的帮助。

推荐答案

它看起来像中奖范围是：

It looks like the winning scope is:

Class Section << ActiveRecord::Base
  scope :teacher_fname_scope, lambda { |n| joins(:teachers).("teachers.first_name = ?", n) }
end

这是有道理的，但我不明白为什么原来没有工作，给瑞恩·贝茨在的 http://railscasts.com/episodes/215-advanced-queries-in-rails-3?view=asciicast

This makes sense but I don't see why the original didn't work, given what Ryan Bates talks about in http://railscasts.com/episodes/215-advanced-queries-in-rails-3?view=asciicast

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