I am new to ruby on rails. As a part of my learning I created a sample application. In the sample app i have 2 models : tweet, user
I defined the relationship in my model, which defines the following : A Tweet has a User , A User has many Tweets. Here is how my code looks like :
class User < ActiveRecord::Base
attr_accessible :user_email, :user_name, :user_password
has_many :tweet
end
class Tweet < ActiveRecord::Base
attr_accessible :post_title
belongs_to :user
end
Now I want to get this updated in my database. I wanted to check if there is anyway this can be updated automatically e.g. running rake db:migrate or something else. Or if I have do it manually ?
Thanks for all your help.
First of all add a column user_id in your tweet table, which will store the user's id, This user_id will be the key to identify the tweets of an user. And then change the line
has_many :tweet
to
has_many :tweets
and it will work.
Thanks
Related
I am trying to create a query in Rails but am having some trouble creating the correct one. Below is my models with their relationships.
class User < ActiveRecord::Base
has_and_belongs_to_many :rsvps, class_name: 'Event'
has_many :albums
end
class Event < ActiveRecord::Base
has_many :albums
has_and_belongs_to_many :attendees, class_name: 'User'
end
class Album < ActiveRecord::Base
belongs_to :user
belongs_to :event
end
I need to get all events a user has "rsvp'ed" to that they haven't uploaded an album to yet. I can find out if a user has uploaded an album to a particular event using the following:
u = User.find(1)
e = Event.find(1)
e.albums.where(user_id: u.id)
I want to be able to run this query on each of the user's rsvp'ed albums. I know I could do something like this:
u.rsvps.delete_if { |e| !e.albums.where(user_id: u.id).blank? }
However, I want to do this all in one query instead of getting the rsvps and then iterating over them and deleting them when necessary.
In order to get all events a user has rsvp'ed to but haven't uploaded an album to yet, you can use the following, which (UPDATE) now also works when a user has not uploaded any albums.
#event_ids = Album.where(user_id: u.id).pluck(:event_id))
#event_ids.empty? ? u.rsvps : u.rsvps.where("id not in (?)", #event_ids)
In addition, this query should work as well.
u.rsvps.where.not(id: Album.where(user_id: u.id).pluck(:event_id))
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 have a datamodel that contains a Project, which contains a list of Suggestions, and each Suggestion is created by a User. Is there a way that I can create a list of all distinct Users that made Suggestions within a Project?
I'm using Mongoid 3. I was thinking something like this, but it doesn't work:
#project = Project.find(params[:id])
#users = Array.new
#users.push(#project.suggestions.user) <-- this doesn't work
Any ideas? Here's my model structure:
class Project
include Mongoid::Document
has_many :suggestions, :dependent => :destroy
...
end
class Suggestion
include Mongoid::Document
belongs_to :author, class_name: "User", :inverse_of => :suggestions
belongs_to :project
...
end
class User
include Mongoid::Document
has_many :suggestions, :inverse_of => :author
...
end
While Mongoid can give MongoDB the semblance of relationships, and MongoDB can hold foreign key fields, there's no underlying support for these relationships. Here are a few options that might help you get the solution you were looking for:
Option 1: Denormalize the data relevant to your patterns of access
In other words, duplicate some of the data to help you make your frequent types of queries efficient. You could do this in one of a few ways.
One way would be to add a new array field to User perhaps called suggested_project_ids. You could alternatively add a new array field to Project called suggesting_user_ids. In either case, you would have to make sure you update this array of ObjectIds whenever a Suggestion is made. MongoDB makes this easier with $addToSet. Querying from Mongoid then looks something like this:
User.where(suggested_project_ids: some_project_id)
Option 2: Denormalize the data (similar to Option 1), but let Mongoid manage the relationships
class Project
has_and_belongs_to_many :suggesting_users, class_name: "User", inverse_of: :suggested_projects
end
class User
has_and_belongs_to_many :suggested_projects, class_name: "Project", inverse_of: :suggesting_users
end
From here, you would still need to manage the addition of suggesting users to the projects when new suggestions are made, but you can do so with the objects themselves. Mongoid will handle the set logic under the hood. Afterwards, finding the unique set of users making suggestions on projects looks like this:
some_project.suggesting_users
Option 3: Perform two queries to get your result
Depending on the number of users that make suggestions on each project, you might be able to get away without performing any denormalization, but instead just make two queries.
First, get the list of user ids that made suggestions on a project.
author_ids = some_project.suggestions.map(&:author_id)
users = User.find(author_ids)
In your Project class add this :
has_many :users, :through => :suggestions
You'll then be able to do :
#users.push(#project.users)
More info on :through here :
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#method-i-has_many
For mongoid, take a look at this answer :
How to implement has_many :through relationships with Mongoid and mongodb?
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.
I am new to Rails and finished Michael Hartl's "Ruby on Rails 3 Tutorial". Although the book teaches me a lot, I find this puzzle I don't understand.
To preview the puzzle, that is, I don't understand, inside User model,
has_many :following, :through=>:relationship, :source=>:followed
how this piece of code link "user.following" to an array of User instances.
And below is the whole puzzle.
First of all, I have the Relationship model, which records followed_id and follower_id infos. Inside Relationship model, the association is simple as
class Relationship < ActiveRecord::Base
attr_accessible :followed_id
belongs_to :follower, :class_name => "User"
belongs_to :followed, :class_name => "User"
end
Then, inside the User model, a user will assume the role of follower, and collect all its following rows in relationships table through relationships association.
class User < ActiveRecord::Base
.
.
.
has_many :relationships, :foreign_key => "follower_id", :dependent => :destroy
.
Until now, I got it.
But confusion came at the next line, where through user.following it can assemble all that user's following(User instances). Like so,
has_many :following, :through=>:relationships, :source=>:followed
I understand that :source=>:followed will overwrite the default, and let find all followed_ids associated with that user.
But, how can Rails recognize followed_id to link to User object? The label name doesn't match users, nor is there :class_name specified. I just don't get how Rails do this underlying work, or I missed out some hints.
Thank you! :)
But, how can Rails recognize followed_id to link to User object? The
label name doesn't match users, nor is there :class_name specified. I
just don't get how Rails do this underlying work, or I missed out some
hints.
Rails recognize that is an user object because it is set in Relationship's belongs_to. What Rails does here is to follow the relationship class through the foreign key "follower_id" and returning every User that has a relationship with the current user as followed. Of course Rails do that in a single SQL statement like this:
SELECT `users`.* FROM `users` INNER JOIN `relationships` ON `relationships`.followed_id = `users`.id WHERE ((`relationships`.follower_id = <the current user id> ))
has_many :following, :through=>:relationships, :source=>:followed
This explains to Rails that following is the inverse relationship of following and that users has many following and followed through his relationships.
The way Rails knows that followed_id is linked to User is that it is defined in your Relationship model.
Hope you've understood ! Good luck :)