我如何获得创建了最后一个主题的最后一个用户

Question

i have 3 models as shown below. In my categories/index.erb.haml I have all the categories showing. I have a column that i want to show the latest topic that a user created and their name as well. I have an example below.

Category
  has_many :topics
Topic
  belongs_to :category
  belongs_to :user
User
  has_many :topics

.categories
- @categories.each do |category|
    .container
        .row
            .col-md-6
                .col-md-3
                    .img
                        = image_tag('first.png')
                .col-md-9
                    %h4.category.name
                        = link_to category.name, category_path(category)
                    %p
                        = category.description
            .col-md-2
                .topic-count
                    %h1
                        = category.topics.count
                .topics
                    Topics
            .col-md-4
                .description
                    %p
                        Last topic by 'user name here' Tue Nov 28, 2015
                        'topic title here'

Answer 1

According to the associations you posted, you should be able to get the user of the last topic by this:

Topic.last.user

Also, mentioned by @marczking in the comment section.

Topic.last will give you the last topic that was created and then Topic.last.user will give you the corresponding user as your Topic model belongs_to a User . In order to make this work, you also need to have a user_id column in the topics table in the database.

Answer 2

If you want to get the last Topic for each Category than you have to loop through the Categories and get the last Topic since you have a relation.

Category.includes(:topics).find_each do |category|
  last_topic_of_the_category = category.topics.last  # <= The last topic
end