計數的hasMany關係/ mongoid

Question

輸入代碼hereI「米目前正在運行通過mongoid MongoDB的一個Rails應用程序。比方說，我有兩個集合，文章和評論，他們正在通過一個HABTM關係聯繫在一起，我想喜歡選擇具有最多評論的帖子，我想這樣做的方式是計算每個崗位和order by comments.count DESC的意見。我不知道怎麼算的意見對每個職位的數量通過這種「僞場」一列添加到帖子結果就像count(comments) AS comments_count在SQL和訂單。

對這個有什麼想法？

感謝

編輯，尋找與此相關的其他人的答案，我已經試過：

db.posts.aggregate([ 
    { $group: { 
    _id: { post_id: '$post_id', comment_id: '$comment_id' } 
    }}, 
    { $group: { 
    _id: '$_id.post_id', 
    comments_count: { $sum: 1 } 
    }}] 
    , function(err, result){ 
    console.log(result); 
    } 
); 

我越來越

{ 
"result" : [{ 
     "_id" : null, 
     "datasets_count" : 1 
    }], 
"ok" : 1 
} 

Answer 1

MongoDB中的聚合框架對分組運營商，總結和分類。 以下是如何分組，計數和評論數排序的職位工作的例子。 希望這是你想要的東西，它可以幫助。

模型/ post.rb

class Post 
    include Mongoid::Document 
    has_many :comments 
    field :text, type: String 
end 

模型/ comment.rb

class Comment 
    include Mongoid::Document 
    belongs_to :post 
    field :text, type: String 
end 

測試/單元/ post_test.rb

require 'test_helper' 
require 'pp' 
class PostTest < ActiveSupport::TestCase 
    def setup 
    Post.delete_all 
    Comment.delete_all 
    end 
    test "posts ordered by comment count" do 
    [ [ "Now is the time for all good men to come to the aid of their country.", 
     [ "Tally ho!" ] ], 
     [ "Twas brillig, and the slithy toves did gyre and gimble in the wabe.", 
     [ "Off with their heads!", 
      "The time has come, the walrus said.", 
      "Curiouser and curiouser." ] ], 
     [ "The quick brown fox jumped over the lazy dog.", 
     [ "The typewriter is mightier than the sword.", 
      "Dachshund is a badger dog." ] ] 
    ].each do |post, comments| 
     post = Post.create(text: post) 
     comments.each{|comment| post.comments << Comment.create(text: comment)} 
    end 
    pipeline = [ 
     { '$group' => { 
      '_id' => '$post_id', 
      'count' => { '$sum' => 1 } 
      } 
     }, 
     { '$sort' => { 'count' => -1} 
     } 
    ] 
    result = Comment.collection.aggregate(pipeline).to_a.collect do |post_id_count| 
     Post.find(post_id_count['_id']) 
    end 
    puts 
    pp result 
    end 
end 

耙測試

運行測試：

[1/1] PostTest#test_posts_ordered_by_comment_count 
[#<Post _id: 52717e7f7f11ba52d8000003, text: "Twas brillig, and the slithy toves did gyre and gimble in the wabe.">, 
#<Post _id: 52717e7f7f11ba52d8000007, text: "The quick brown fox jumped over the lazy dog.">, 
#<Post _id: 52717e7f7f11ba52d8000001, text: "Now is the time for all good men to come to the aid of their country.">] 
Finished tests in 0.050494s, 19.8043 tests/s, 0.0000 assertions/s. 
1 tests, 0 assertions, 0 failures, 0 errors, 0 skips