I am new to both DBs and Rails (using 3.2), and I suspect this is a basic question that I'm just having trouble finding an answer for.
I'm making an app that tracks articles people submit to journals. So, each user has a number of articles. For each article, they can submit it to a number of journals. The submission object itself keeps track not only of the article being submitted and the journal it's submitted to, but also the date it was submitted, the way it was submitted (email, online system, etc.), the date a response was received (if any), the response (if any) (e.g. accepted, resubmit, decline).
I'm trying to allow a user to view all of their outstanding submissions in one place. So, for each user, I'm trying to query the db to get all submissions belonging to articles that belong to that user, but only returning the submissions for which response is NULL (meaning there is no response yet, and thus the submission is still outstanding).
So my models are related like this:
class User < ActiveRecord::Base
has_many :articles
end
class Article < ActiveRecord::Base
belongs_to :user
has_many :submissions
end
class Journal < ActiveRecord::Base
has_many :submissions
end
class Submission < ActiveRecord::Base
belongs_to :article
has_one :journal
end
Now, for a given #user, I think I could do something like
#articles_with_subs = #user.articles.joins(:submissions)
and then
#out_subs = Array.new
#articles_with_subs.each do |article|
outs = article.submissions.where("response NOT NULL")
#out_subs.push outs
end
#out_subs.flatten!
but that seems pretty inefficient. What probably big, obvious thing am I missing?
Thanks very much.
#out_subs = Submission.where("response NOT NULL")
.joins(:article).where(:article => {:user_id => #user.id})
Related
I have a polymorphic association in a Rails 3 app where a User may favorite objects of various classes.
class Favorite < ActiveRecord::Base
belongs_to :user
belongs_to :favoriteable, :polymorphic => true
end
class User < ActiveRecord::Base
has_many :favorites
end
class Image < ActiveRecord::Base
has_many :favorites, :as => :favoriteable
end
class Video < ActiveRecord::Base
has_many :favorites, :as => :favoriteable
end
I would like to be able return a list of just a User's favorite_images for example.
user.favorite_images #returns a list of the images associated with the user via :favoritable
I'm guessing there is a straightforward way of doing this but I haven't been able to figure it out. Let me know if you need anymore info.
Thanks!
===edit====
I know that I could retrieve what I am looking for via
favorite_images = user.favorites.collect{|f| if f.favoriteable_type=='Image'; f.favoriteable; end}
I could define an instance method for the User class and put that inside. I was wondering if there is a way to do it as some sort of has_many association. Really just because going forward it would be easier to have all that in one place.
When you created the table for Favorite you created a couple of columns favoriteable_id and favoriteable_type and you can use this information to restrict your query.
If you do user.favorites you will get all of the favorites and to restrict them to say just the images then you can do user.favorites.where(favoriteable_type: 'image') but that just gives you the favorite records and it sounds like you want the actual images. To get those you can do it by then mapping and pulling the favoriteable out. You'll likely want to include it in the query though so you don't hit the database so much. I would also make this a method on User.
def favorite_images
favorites.includes(:favoriteable).where(favoriteable_type: 'Image').map(&:favoriteable)
end
I'm adding quiz functionality to the twitter app from the Hartl tutorial and have these Models:
User is nearly the same as the tutorial:
class User < ActiveRecord::Base
has_many :followed_users, through: :relationships, source: :followed
has_many :takens, dependent: :destroy
has_many :questions, through: :takens
end
Taken is a table of Question ids to User ids:
class Taken < ActiveRecord::Base
belongs_to :user
belongs_to :question
end
nothing interesting in Question:
class Question < ActiveRecord::Base
attr_accessible :category, :correct, :option1, :option2, :option3, :qn
end
I want to be able to show followed_users and followers in order of the number of tests they have taken. In the console this can be had through:
User.find_by_id(1).question_ids.count
Then I can do something like:
User.find_by_id(1).followers.first.question_ids.count
in the console to get the count for a single follower.
I feel like I'm almost there.
How do I sort the followers and followed_users through their 'takens' count? (I was also looking at cache_count, which at first seemed promising, but might not be what I need...)
Ruby on Rails does not provide an object oriented mechanism to perform this; you have to write the SQL yourself. In your case, I'd say that the following line SHOULD work:
User.find_by_sql("SELECT users.*, COUNT(questions.id)
AS c FROM users, questions WHERE questions.user_id = users.id
GROUP BY users.id ORDER BY c DESC")
I don't have the actual tables in front of me, so I can't be sure that this is actual valid SQL, but hopefully it should work.
EDIT: There were a few syntax errors with my SQL but they've been fixed. Note that I'm assuming that your tables are called users and questions. They may differ for you.
I am working with a has_many through for the first time, and despite a lot of reading here and in the guide I am not understanding the correct way to access attributes on the through table. My tables are the same as this example from another post.
class Product < ActiveRecord::Base
has_many :collaborators
has_many :users, :through => :collaborators
end
class User < ActiveRecord::Base
has_many :collaborators
has_many :products, :through => :collaborators
end
class Collaborator < ActiveRecord::Base
belongs_to :product
belongs_to :user
end
Assuming that the collaborators table has additional attributes, say hours_spent, what is the correct way to find the hours_spent from the collaborator table for a particular user and product?
When I have found my users via the product, and am iterating over them as in
#product.users.each do |user|
This seems to work
user.collaborator[0].hours_spent
I get the correct value, but since there should only be one collaborator record for each User/Product pair, the index is throwing me off, making me think I’m doing something wrong.
Thank you for reading!
EDIT
Perhaps I am not getting the has_many through concept. Maybe a MySQL example would help.
What I was thinking is that if I did
SELECT * FROM collaborators where user_id = 1;
I would expect a set (zero or more) as the result. Similarly
SELECT * FROM collaborators where product_id = 1;
would also give me a set, but
SELECT * FROM collaborators where user_id = 1 and product_id = 1;
would give at most 1 row.
If I am understanding properly, all 3 queries return a set. So I guess I need some kind of uniqueness constraint, but that would have to be a compound key of sorts, on both of the belongs to keys. Is that even possible? Is there a structure that better models this?
Thanks so much for the quick and helpful responses!
There may be a single database row per pair, but when considering a single user, that user can be associated to many products, so a user can have many rows in the collaborators table. Similarly, when considering a single product, that product can be associated to many users, so a product can have many rows in the collaborators table.
Also, instead of using user.collaborators[0].hours_spent, use user.collaborators.first.try(:hours_spent) (which may return null), if you only want the first collaborator's hours spent.
If a single user can only have one single product and a single product can only have a single user, then switch the has_many's to has_one's for everything.
Update: The preceding is the answer to the original question which has since been clarified via comments. See comments for detail and see comments on other answer by Peter.
Perhaps you should use has_and_belongs_to_many. If your Collaborator is used only to make link between User and Product without having more fields.
class Product < ActiveRecord::Base
has_and_belongs_to_many :users
end
class User < ActiveRecord::Base
has_and_belongs_to_many :products
end
The beetween migration would be:
class CreateUsersProducts < ActiveRecord::Migration
def change
create_table "users_products", :id => false do |t|
t.integer :user_id
t.integer :product_id
end
end
end
After implementing this, what I found was that I think I had the correct relationships setup, I had to use the has_many :though as users could have many products, and it needed to be :through because there are additional attributes on the collaborator table. The sticking point was how to get there to only be a single Collaborator record for each user/product pair, and then how do I guarantee I got it. And to this point the answer I've found is it has to be done in code.
To make sure there is only a single record for each pair, I used
class Collaborator < ActiveRecord::Base
validates :product_id, :presence => true, :uniqueness => {:scope => [:user_id], :message => "This is a duplicate join"}
And then to make doubly sure I'm finding the right record, I have a scope
scope :collaboration_instance, lambda {|p_id, u_id| where("collaborations.product_id = ? && collaborations.user_id = ?", p_id, u_id)}
If someone has a more elegant solution, or just wants to improve this one, please post and I will change yours to the selected answer.
Let's assume I have two models.
class User < ActiveRecord::Base
has_one :blog
end
class Blog < ActiveRecord::Base
belongs_to :user
validates_presence_of :user
validates_uniqueness_of :user_id
end
Let's assume I have one user with a blog. For some reason, let's pretend I call create_blog for the same user (I know it should not be an option since the user already has a blog). If this blog doesn't pass the validations, and it won't, not only isn't saved, but it deletes the previous blog the user has.
Why is this happening? Why the initial blog gets deleted? Is this behavior expected or is there something I missing?
By calling create_blog you're telling Rails to discard the previous blog. There isn't a way around this (that I am aware of) that doesn't involve doing something like this:
blog = Blog.new(params[:blog])
if blog.valid?
user.blog = blog
user.save
end
I print in my view a number that tell me, how many people read my article. It looks something like a:
<%=article.hits.count%>
As is possible to see, I created a simple association.
Now I am trying to get the information, if the user who is log in on my page, so if he is already had read this article. In my table that contains hits is column user_id.
But I can't still find the way, how to get...
I tried something like:
<% if session[:login_user_id].hits.user_id == session[:login_user_id]%>
Have you read it already.
<% end %>
But the example above doesn't work me... Could anyone help me please, how to do?
EDIT: The models:
class Article < ActiveRecord::Base
has_many :hits
end
class Hits < ActiveRecord::Base
belongs_to :article, :class_name => "DataHit", :foreign_key => "article_id"
has_many :users
end
class User < ActiveRecord::Base
belongs_to :hit
end
Thanks in advance
Let's first talk about the model you like to receive. For me, it sounds like:
Every article can be visited / read by many users.
Every user can read / visit many articles.
This is a classical n:m-association which is normally implemented by a has-many-through association.
If this is the intention, it should be implemented like:
class Article < ActiveRecord::Base
has_many :hits
has_many :users, :through => :hits
end
class Hits < ActiveRecord::Base
belongs_to :article, :class_name => "DataHit", :foreign_key => "article_id"
belongs_to :user
end
class User < ActiveRecord::Base
has_many :hits
has_many :articles, :through => :hits
end
Of course, you have to add migrations that ensure that the final DB model is like that:
Hit has article_id and user_id to ensure that users may find the articles they have read
If you have that model implemented, it should be more easy. Then you have operations available like: #article.users.contains(User.find(user_id)). Have a look at the tutorial at Ruby on Rails Guides which explain what the has-many-through relation is and which advantages they have.
It would be helpful if you try the things first in the console of Rails. To do that, start with:
Start the rails console in the root directory of your application: rails c
Enter there e.g.: art = Article.find(1) to get the article with the id.
Try which methods are available: art.methods.sort to see all methods that could be used. If there is no method users, you have did something wrong with the assocication.
Try the call: us = art.users and look at the result. It should be a rails specific object, an object that behaves like a collection and understands how to add and remove users to that collection (with the whole life cycle of rails). The error your currently have could mean different things:
Your database model does not match your associations defined in Rails (I suspect that).
Some minor tweak (misspelling somewhere) which hinders Rails.
I hope this gives you some clues what to do next, I don't think that we can fix the problem here once and for all times.