Active Record查询

Question

I have two models ForumThread and Post set-up like this:

class ForumThread < ActiveRecord::Cached
    has_many :posts
end

class Post < ActiveRecord::Cached
end

class CreateForumThreads < ActiveRecord::Migration
    def self.up
        create_table :forum_threads do |t|
            t.column :thread_name, :text
        end

        add_index :forum_threads, :thread_name
    end

    def self.down
        drop_table :forum_threads
    end
end

class CreatePosts < ActiveRecord::Migration
    def self.up
        create_table :posts do |t|
            t.column :post_body, :text
            t.integer :forum_thread_id, :null => false
            t.integer :priority
        end
    end

    def self.down
        drop_table :posts
    end
end

I'd like to create a query that returns all forum threads where there's at least one post in each thread with priority of one. How do I create this query?

I've been considering something like ForumThread.joins(:posts).select(:priority => 1) . I'm relatively new to Active Record (and totally new to joins) so any help is appreciated.

Answer 1

ForumThread.joins(:posts).where(:posts => {:priority => 1})

看看加入条件

Answer 2

First of all you should rename thread_id field to forum_thread_id in posts table and add posts_count to forum_threads table.

In Post class add belongs_to :forum_thread, :counter_cache => true

Now you can query ForumThread.where("posts_count > ?", 1).joins(:posts).where("posts.priority = ?", 1) which will return you a collection of posts.