如何在Ruby中为'每个循环'创建这个？

Question

Given:

class Author < ActiveRecord::Base
  has_many :articles
end

Upon receipt of a JSON file that includes the author's articles, I'd like to destroy the articles that are in the database for the author, but not included in the JSON file. How can I create this 'for each loop'?

article_collection = @author.articles.all
unless article_collection.blank?
  article_collection.each do |article_from_collection|
    # How can I check on the next line if it's id is included in the params?
    if article_from_collection.arti_id "is not part of" params[:author][:articles_attributes]
      article_from_collection.destroy
    end
  end
end

How can I check on the 5th line, on basis of arti_id which is also included in the params, whether the article with that arti_id exists in the JSON input?

Should I perhaps build a collection of arti_id s in the parameters and then use .include? to see for each article in the DB, if it is in this collection?

I tried the two lines below. The first returns false irrespective whether the article is included in the json or not. The second line returns the error TypeError Exception: no implicit conversion of Symbol into Integer .

if params[:author][:articles_attributes].include? article_from_collection.arti_id
if params[:author][:articles_attributes][:arti_id].include? article_from_collection.arti_id

params[:author] returns something like:

{ "some_other_attributes"=>[ {"key"=>"value", ...},
                             {...} ],
  "articles_attributes"=>  [ {"arti_id"=>"string-id", "other_attributes"=>"value", ...},
                             {"arti_id"=>"string-id", "other_attributes"=>"value", ...} ]
}

Answer 1

You could do this with an ActiveRecord query

article_ids = params[:author][:article_attributes].map do |attrs|
  attrs[:arti_id]
end

@author.articles.where.not(id: article_ids).destroy_all

This will destroy all articles for the author whose ids are not in the article attributes you've been given.

If you're confused about the query, it simply creates a NOT IN query which filters out the articles passed in and then destroys the ones that are left over.

Answer 2

For this, you can first map out all the arti_id in a separate array variable, and then use the include? method or the exclude? method to check if a particular id is in the array.

Example:

article_ids = params[:author][:articles_attributes].map{ |art_attr| art_attr[:arti_id] }

and then in the loop: ( for using the include? method )

article_collection = @author.articles.all
unless article_collection.blank?
  article_collection.each do |article_from_collection|
    # This is how you can handle it...
    unless article_ids.include? article_from_collection.arti_id 
      article_from_collection.destroy
    end
  end
end

or if you will prefer using exclude ?

article_collection = @author.articles.all
unless article_collection.blank?
  article_collection.each do |article_from_collection|
    # This is how you can handle it...
    if article_ids.exclude? article_from_collection.arti_id 
      article_from_collection.destroy
    end
  end
end

Answer 3

How about something like the following:

article_collection = @author.articles.all
params_article_ids = params[:author][:articles_attributes].collect{ |article_attrs| article_attrs[:arti_id]}

article_collection.reject{ |art| present_article_ids.include?(art.id)}.each(&:destroy)

Answer 4

I assume your params[:author][:articles_attributes] holds hashes of article attributes where each of them has an arti_id.

At first I would return all article ids of the author:

all_article_ids = @author.articles.pluck(:arti_id)

Second, I collect all arti_ids from your article attributes you want to keep save:

ids = params[:author][:articles_attributes].map{|attr| attr.arti_id}

Now there are two arrays of ids. I subtract the "ids" array from the "all_article_ids" and I get a new array of ids, which are not in the "ids" array. These are the ids of "all_article_ids", which should be destroyed.

@author.articles.destroy(all_article_ids - ids)

Is this what fits your needs?