On blog app I want to display list of tags with articles.
class Article < AR::B
has_and_belongs_to_many :tags
end
class Tag < AR::B
has_and_belongs_to_many :articles
end
What would Tag scope look like?
Tag.joins(:articles) ... # should return tags associated to at least 1 article
One way to do this with Ruby/Rails would be this one.
Tag.includes(:articles).select { |tag| tag.articles.any? }
.includes makes sure that the articles are loaded alongside the tags, which is more efficient than loading them when every tag's articles are iterated upon.
The array is then parsed to only select the ones with articles associated.
Related
I originally asked this question about acts_as_tree but it seems to be more general so I'm rephrasing it a bit here.
I have a model "category" using acts_as_tree. I often find myself needing to join it with other models for various queries, but I don't know how to use the provided scopes such as children, ancestors, siblings, descendants to create the conditions that I need.
Concrete example:
class Category < ActiveRecord::Base
acts_as_tree
has_many :photo
end
class Photo
belongs_to :category
end
cat = Category.first
How can I query for all the photos of children of cat or all the photos of its siblings?
Seems like I need something like:
Photo.joins(cat.children)
Photo.joins(cat.siblings)
which I know is not a valid code.
Since act_as_tree doesn't really use scopes but methods that return results, you can do it like:
class Photo
belongs_to :category
scope :from_category, -> (category) {
joins(:category).where(category: category)
}
end
cat = Category.first
Photo.from_category(cat.children)
Photo.from_category(cat.siblings)
And that should work.
I want to create an activity feed from recent article and comments in my rails app. They are two different types of activerecord (their table structures are different).
Ideally I would be able to create a mixed array of articles and comments and then show them in reverse chronological order.
So, I can figure out how to get an array of both articles and comments and then merge them together and sort by created_at, but I'm pretty sure that won't work as soon as I start using pagination as well.
Is there any way to create a scope like thing that will create a mixed array?
One of the other problems for me, is that it could be all articles and it could be all comments or some combination in between. So I can't just say I'll take the 15 last articles and the 15 last comments.
Any ideas on how to solve this?
When I've done this before I've managed it by having a denormalised UserActivity model or similar with a belongs_to polymorphic association to an ActivitySource - which can be any of the types of content that you want to display (posts, comments, up votes, likes, whatever...).
Then when any of the entities to be displayed are created, you have an Observer that fires and creates a row in the UserActivity table with a link to the record.
Then to display the list, you just query on UserActivity ordering by created_at descending, and then navigate through the polymorphic activity_source association to get the content data. You'll then need some smarts in your view templates to render comments and posts and whatever else differently though.
E.g. something like...
user_activity.rb:
class UserActivity < ActiveRecord::Base
belongs_to :activity_source, :polymorphic => true
# awesomeness continues here...
end
comment.rb (post/whatever)
class Comment < ActiveRecord::Base
# comment awesomeness here...
end
activity_source_observer.rb
class ActivitySourceObserver < ActiveRecord::Observer
observe :comment, :post
def after_create(activity_source)
UserActivity.create!(
:user => activity_source.user,
:activity_source_id => activity_source.id,
:activity_source_type => activity_source.class.to_s,
:created_at => activity_source.created_at,
:updated_at => activity_source.updated_at)
end
def before_destroy(activity_source)
UserActivity.destroy_all(:activity_source_id => activity_source.id)
end
end
Take a look at this railscast.
Then you can paginate 15 articles and in app/views/articles/index you can do something like this:
- #articles.each do |article|
%tr
%td= article.body
%tr
%td= nested_comments article.comment.descendants.arrange(:order => :created_at, :limit => 15)
This assumes the following relations:
#app/models/article.rb
has_one :comment # dummy root comment
#app/models/comment.rb
belongs_to :article
has_ancestry
And you add comments to an article as follows:
root_comment = #article.build_comment
root_comment.save
new_comment = root_comment.children.new
# add reply to new_comment
new_reply = new_comment.children.new
And so forth.
I have articles and categories in a n:m relation:
I looking for a find statement on the Category Model so that I can get all categories witch consist at least one article.
Should be easy, but I didn't find a efficient solution, without searching retrieving all the articles.
Thanks,
Maechi
I think that counter cache is your friend here. Take a look here.
You can add the counter cache to the categories table and in the CategoryArticles you do like
class CategoryArticles
belongs_to :article
belongs_to :category, :counter_cache => true
end
So you can find your Category with
#categories = Category.find(:all, :conditions => ["category_articles_count > ?", 0])
I have a rails app (running on version 2.2.2) that has a model called Product. Product is in a has-and-belongs-to-many relationship with Feature. The problem is that I need have search functionality for the products. So I need to be able to search for products that have a similar name, and some other attributes. The tricky part is that the search must also return products that have the exact set of features indicated in the search form (this is represented by a bunch of checkboxes). The following code works, but it strikes me as rather inefficient:
#products = Product.find(:all, :conditions=>["home=? AND name LIKE ? AND made_by LIKE ? AND supplier LIKE ? AND ins LIKE ?",hme,'%'+opts[0]+'%','%'+opts[1]+'%','%'+opts[3]+'%','%'+opts[4]+'%'])
#see if any of these products have the correct features
if !params[:feature_ids].nil?
f = params[:feature_ids].collect{|i| i.to_i}
#products.delete_if {|x| x.feature_ids!=f}
end
I'm sorry that my grasp of rails/sql is so weak, but does anyone have any suggestions about how to improve the above code? Thanks so much!
First, i would recommend you to manually write a FeatureProduct model (and not use the default 'has_and_belongs_to_many')
EG
class FeatureProduct
belongs_to :feature
belongs_to :product
end
class Product
has_many :feature_products
has_many :features, :through => :feature_products
end
class Feature
has_many :feature_products
has_many :products, :through => :feature_products
end
For the search: You may find the gem SearchLogic to be exactly what you need. It has support for 'LIKE' conditions (it means that you can write in a more 'Rails way' your query). It also has support for performing a search with conditions on a related model (on your Feature model, to be more precise).
The solution would be something like:
search = Product.search
search.name_like = opt[0]
search.made_by_like = opt[1]
...
search.feature_products_id_equals = your_feature_ids
..
#product_list = search.all
There is also an excellent screencast explaining the use of this gem.
Good luck :)
Say if #news_writers is an array of records. I then want to use #news_writers to find all news items that are written by all the news writers contained in #news_writers.
So I want something like this (but this is syntactically incorrect):
#news = News.find_all_by_role_id(#news_writers.id)
Note that
class Role < ActiveRecord::Base
has_many :news
end
and
class News < ActiveRecord::Base
belongs_to :role
end
Like ennen, I'm unsure what relationships your models are supposed to have. But in general, you can find all models with a column value from a given set like this:
News.all(:conditions => {:role_id => #news_writers.map(&:id)})
This will create a SQL query with a where condition like:
WHERE role_id IN (1, 10, 13, ...)
where the integers are the ids of the #news_writers.
I'm not sure if I understand you - #news_writers is a collection of Role models? If that assumption is correct, your association appears to be backwards - if these represent authors of news items, shouldn't News belong_to Role (being the author)?
At any rate, I would assume the most direct approach would be to use an iterator over #news_writers, calling on the association for each news_writer (like news_writer.news) in turn and pushing it into a separate variable.
Edit: Daniel Lucraft's suggestion is a much more elegant solution than the above.