Could you tell me if there is a better way.
Models:
class Skill
has_many :tags
has_many :positions
end
class Tag
belongs_to :skill
has_and_belongs_to_many :positions
end
class Position
belongs_to :skill
has_and_belongs_to_many :tags
end
I want to list all skills and the tags of their positions. Like this:
skill - tag tag tag tag
skill - tag tag
...
I managed to acheive it like this:
<% #skills.each do |skill| %>
<%= skill.name %>
<% skill.positions.collect{|p| p.tags}.flatten.uniq.each do |t| %>
<%= t.name %>
<% end %>
<% end %>
And my skills_controller:
def index
#skills = Skill.all
end
Is this the right way?
Since tagging is a pretty common problem I'd recommend taking a look at acts-as-taggable-on, a widely used and very good gem for adding tags to any Rails model.
Regardless, your models look pretty good (except that has_and_belongs_to_many is often eschewed in favor for has_many :through), but I do see room for improvement here:
<% skill.positions.collect{|p| p.tags}.flatten.uniq.each do |t| %>
<%= t.name %>
<% end %>
Firstly, this is a lot of business logic to put in your view. You should do this in your controller instead. Secondly, it would be more performant to do it the other way around:
#tags = Tag.all :conditions => [ "tag.id IN (?)", skill.positions.map &:id ]
There are more efficient ways still to do this, but this ought to give you an idea.
First off - with any performance question you should measure the performance. Create twice as many skills, tags, and positions as you expect to need in a rake task. Then measure the page load times. If they're OK for your needs, cool. Otherwise, keep reading.
This is not particularly efficient since you will go across the network to the database for every skill to position mapping, and then again for every position to tag mapping. You can use the includes method to load using fewer queries - see the Rails guide on querying.
Related
Suppose there is a blog with posts, comments and users which can comment. Users have SEO-friendly URLs such as http://localhost:3000/users/john (this can be easily done by using permalink_fu).
The model uses touch to simplify caching:
class Post
has_many :comments
end
class Comment
belongs_to :post, :touch=>true
end
And the view code would be something like this:
<%= cache #post do %>
<h1><%= #post.title %></h1>
<%= #post.content %>
<%= #post.comments.each do |comment| %>
<%= link_to h(comment.user), comment.user %> said:
<%= comment.content %>
<% end %>
<% end %>
Now suppose John changes his nick to Johnny -- his URL changes to http://localhost:3000/users/johnny. Because of doing fragment caching on posts and comments, John's comments will point to John's wrong URL unless the fragment is expired. It can be possible to manually touch or expire all posts that contain comments by John in this example, but in a complex application this would require very complex queries and seems very error-prone.
What's the best practice here? Should I use non-SEO-friendly URLs such as /users/13 instead of /users/john ? Or maybe keep a list of old URLs until the cache is expired? No solution looks good to me.
EDIT: Please note this is just a simplified example -- it's definitely very simple to query posts and touch them in this case. But a complex app implies many relationships among objects which makes it hard to track every object that has a reference to a user. I've researched a bit on this -- Facebook only allows setting your username once, so this problem doesn't exist.
I don't see it would be complex to expire cached posts. Set up a sweeper:
class UserSweeper < ActionController::Caching::Sweeper
observe User
def after_save(user)
user.comments.collect(&:post).each do |post|
expire_fragment post
end
end
I'd use a before_save filter for example
class User
has_many :posts
before_save :touch_posts
private
def touch_posts
Post.update_all({:updated_at => Time.now}, {:user_id => self.id}) if self.login_changed?
true
end
end
One query to update every user's post. Not really complex.
To simplify things, I have 3 tables :
Person
has_many :abilities, through => :stats
Ability
has_many :people, through => :stats
Stats
belongs_to :people
belongs_to :abilities
Stats has an extra attribute called 'rating'.
What I'd like to do is make an edit person form that always lists all the abilities currently in the database, and lets me assign each one a rating.
For the life of me, I can't figure out how to do this. I managed to get it to work when creating a new user with something like this:
(from the people controller)
def new
#character = Character.new
#abilities = Ability.all
#abilities.each do |ability|
#person.stats.build(:ability_id => ability.id )
end
end
From the people form:
<% for #ability in #abilities do %>
<%= fields_for "person[stats_attributes]" do |t| %>
<div class="field">
<%= t.label #ability.name %>
<%= t.hidden_field :ability_id, :value => #ability.id, :index => nil %>
<%= t.text_field :rating, :index => nil %>
</div>
<% end %>
<% end %>
This successfully gives me a list of abilities with ratings boxes next to them, and lets me save them if i'm making a new user.
The problem is that if I then load up the edit form (using the same form partial), it doesn't bring back the ratings, and if I save, even with the exact same ratings, it creates duplicate entries in the stats table, instead of updating it.
I realize I'm a terrible programmer and I'm probably doing this the wrong way, but how do I get the edit form to recall the current ratings assigned to each ability for that user, and secondly how do i get it to update the rating instead of duplicating it if the combination of person and ability already exists?
Shouldn't that be
Character
has_many :stats
has_many :abilities, through => :stats
Ability
has_many :stats
has_many :characters, through => :stats
Stat
belongs_to :character
belongs_to :ability
?
Also, is it Person or Character? You refer variously to both. (I'm going to go with Character in my answer)
I think you've fallen foul of the "I'll try to make a simplified version of my schema in order to attempt to illustrate a problem but instead make things more complex and muddle the issue by screwing it up so it doesn't make sense" syndrome. Anyway, there's a couple of issues i can see:
1) first thing is that you're adding all the possible abilities to a character as soon as they're created. This is silly - they should start out with no abilities by default and then you create join table records (stats) for the ones they do have (by ticking checkboxes in the form).
2) A simple way to manipulate join records like this is to leverage the "ability_ids=" method that the has_many :abilities macro gives you - referred to as "collection_ids=" in the api http://railsbrain.com/api/rails-2.3.2/doc/index.html?a=M001885&name=has_many
In other words, if you say
#character.ability_ids = [1,12,30]
then that will make joins between that character and abilities 1, 12 and 30 and delete any other joins between that character and abilities not in the above list. Combine this with the fact that form field names ending in [] put their values into an array, and you can do the following:
#controller
def new
#character = Character.new
#abilities = Ability.all
end
#form
<% #abilities.each do |ability| %>
<div class="field">
<%= t.label #ability.name %>
<%= check_box_tag "character[ability_ids][]" %>
</div>
<% end %>
#subsequent controller (create action)
#character = Character.new(params[:character]) #totally standard code
Notice that there's no mention of stats here at all. We specify the associations we want between characters and abilities and let rails handle the joins.
Railscasts episodes 196 and 197 show how to edit several models in one form. Example shown there looks similar to what you're trying to do so it might help you out (same episodes on ascicasts: 196, 197).
I am not sure what I am doing wrong here. I find many examples that show that I am doing this right and it is really basic stuff, I know.
I am simplyfying a bit, but I have two models, 'Post' and 'Category'. I am trying to get the list of categories from the database and list them by name.
class Post < ActiveRecord::Base
has_and_belongs_to_many :categories
end
class Category < ActiveRecord::Base
has_and_belongs_to_many :posts
end
# get all categories and output the names
cats = Category.all
cats.each do |cat|
cat.name
end
It instead seems to output the entire array of retrieved results. All results not even just the one I am iterating over. What gives?
Where are you putting that .each loop code? Where is the "output" code you're referring to? If you're using a loop in a view, make sure you're using
<% %>
and not
<%= %>
for the loop lines themselves. As in:
<% Category.all.each do |cat| %>
<%= cat.name %>
<% end %>
Category.all returns an array of all Category objects, which is everything the categories table contains. cats is therefore an array of all the categories. I'm not sure why you think you're only iterating over "one" of anything. To get one result, you can use find() or first:
cat = Category.first
puts cat.name
If you want all the names, you can do this:
Category.all.map(&:name)
or, a bit more efficiently, especially if there are many fields:
Category.all(:select => :name).map(&:name)
I have a country model and a places model - a country has_many places, and a place belongs_to a country. A place model also has_many posts (which belong_to a place). I would like to aggregate all the posts from places that belong to a certain country into a feed - rather like a friend activity feed on a social networking site. I'm having a bit of trouble figuring out the appropriate search to do, any help would be much appreciated! At the moment I have:
country.rb
has_many :places
has_many :posts, :through => :places
def country_feed
Post.from_places_belonging_to(self)
end
post.rb
belongs_to :place
scope :from_places_belonging_to, lambda { |country| belonging_to(country) }
private
def self.belonging_to(country)
place_ids = %(SELECT place_id FROM places WHERE country_id = :country_id)
where("place_id IN (#{place_ids})", { :country_id => country })
end
end
Then in the country show.html.erb file:
<h3>Posts</h3>
<% #country.country_feed.each do |post| %>
<%= link_to "#{post.user.username}", profile_path(post.user_id) %> posted on <%=link_to "#{post.place.name}", place_path(post.place_id) %> <%= time_ago_in_words post.created_at %> ago:
<%= simple_format post.content %>
<% end %>
This runs without any errors, but gives a feed of all the posts, rather than selecting the posts for that particular country. What's the best way to get this working? I've got a sneaking suspicion that I might be over-complicating matters...thanks in advance!
It looks like there's a syntax error in the subquery. places_id does not exist in the places table, so it really ought to read:
SELECT id FROM places WHERE country_id = :country_id
You'd think the invalid subquery would raise an exception, but it doesn't -- or else it is handled silently. Very odd.
But unless I'm missing something, you could replace all this just by using:
<% #country.posts.each do |post| %>
No?
Based on following models
class Company < ActiveRecord::Base
has_and_belongs_to_many :origins
end
class Origin < ActiveRecord::Base
has_and_belongs_to_many :companies
end
I want to have in my companies/_form a collection of checkboxes representing all origins.
Don't know if the Company.new(params[:company]) in companies_controller#create can create the association between company and the selected origins?
I'm running rails 3.0.0, what is the best way to achieve that?
thanks for your insights
habtm isn't a popular choice these days, it's better to use has_many :through instead, with a proper join model in between. This will give you the method Company#origin_ids= which you can pass an array of origin ids to from your form, to set all the associated origins for #company. eg
<% current_origin_ids = #company.origin_ids %>
<% form_for #company do |f| %>
<label>Name:<%= f.text_field :name %></label>
<% Origin.all.each do |origin| %>
<label><%= origin.name %>
<%= check_box_tag "company[origin_ids][]", origin.id, current_origin_ids.include?(origin.id) %>
</label>
<% end %>
<% end %>
As an aside, using a proper join model, with corresponding controller, allows you to easily add/remove origins with AJAX, using create/delete calls to the join model's controller.
I have to agreed with #carpeliam a has_many :through should not be the default choice. A HABTM works fine and involves less code. It also does not restrict the use of ajax and does expose a origin_ids setter to which you can pass an array of ids. Therefore the screencast, whilst from 2007, still works with Rails 3. The other option if using simple_form is this:
= form.association :origins, :as => :check_boxes
Personally I'm not of the belief that has-many-through is always better, it really depends on your situation. Has-many-through is better if there is ANY possibility of your join model having attributes itself. It's more flexible to change. It removes the magic of some Rails conventions. If however you don't need has-many-through, then there's an old RailsCast for HABTM checkboxes that might come in handy.