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[英]Rails: Show all associated records on a has_many through association
[英]Rails 3 find all associated records has_many :through
我想列出與某個特定類別和課堂相關的所有帖子。
我有:
class Post < ActiveRecord::Base
has_many :category_posts
has_many :categories, :through => :category_posts
has_many :classroom_posts
has_many :classrooms, :through => :classroom_posts
end
class Category < ActiveRecord::Base
has_many :category_posts
has_many :posts, :through => :category_posts
end
class CategoryPost < ActiveRecord::Base
belongs_to :category
belongs_to :post
end
class Classroom < ActiveRecord::Base
has_many :classroom_posts
has_many :posts, :through => :classroom_posts
end
class ClassroomPost < ActiveRecord::Base
belongs_to :classroom
belongs_to :post
end
我想做這樣的事情
Post.where(["category.id = ? AND classroom.id = ?", params[:category_id], params[:classroom_id]])
這確實是非常簡單的任務,但我不知道我應該尋找什么(關鍵字)。
這就像同樣的問題, 這個 ,但是在軌道上。
編輯 :我在問題中添加了更多細節。 這有效,但前提是我指定了兩個參數。 女巫並非總是如此 - 我不知道會指定什么樣的參數。
Post.joins(:categories, :classrooms).where(["categories.id = ? AND classrooms.id = ?", params[:classroom_id], params[:category_id]])
這是我在Rails 3中要做的:
在post.rb
:
def self.in_category(category_id)
if category_id.present?
join(:category_posts).where(category_posts: {category_id: category_id})
else
self
end
end
def self.in_classroom(classroom_id)
if classroom_id.present?
join(:classroom_posts).where(classroom_posts: {classroom_id: category_id})
else
self
end
end
我不加入Classroom
或Category
因為它為DBMS做了更多的工作,這不是必需的。
現在,您可以:
Post.in_category(params[:category_id]).in_classroom(params[:classroom_id])
我沒有測試過它。 因此,如果需要,請不要猶豫。
我認為應該有效:
Post.joins(:category_posts, :classroom_posts)
.where(
["category_posts.category_id = ?
AND classroom_posts.classroom_id = ?", params[:category_id], params[:classroom_id]])
這將轉換為SQL,如:
SELECT
p.*
FROM
posts AS p
INNER JOIN
category_posts AS cap ON cap.id = p.category_posts_id
INNER JOIN
classroom_posts AS clp ON clpid = p.classroom_posts_id
WHERE
cap.category_id = '1' AND clp.classroom_id = '1'
;
至於是否使用:include或join on Post
在stackoverflow上查看這個答案 。
聽起來你需要一個if語句。
if params[:category_id] && params[:classroom_id]
Post.joins(:categories, :classrooms).where("classrooms.id" => params[:classroom_id], "categories.id" => params[:category_id]])
elsif params[:category_id]
Category.find(params[:category_id]).posts
else
Classroom.find(params[:classroom_id]).posts
end
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