So im working on a rails app for users to create events (and attend other created events). You can read about the assignment here (for the Odin Project): https://www.theodinproject.com/courses/ruby-on-rails/lessons/associations
Anyways I thought I had understood many to many relationships in rails, but the way i've seen other people write the models is confusing to me.
To me it seems like it should be something like:
class User < ApplicationRecord
has_many :attendances
has_many :events, through: :attendances
end
class Attendance < ApplicationRecord
belongs_to :user
belongs_to :event
end
class Event < ApplicationRecord
has_many :users
has_many :users, through: :attendances
end
This makes sense to me because a User can create many events, and an event can have many users attending. (Although attendances is probably the wrong word, maybe invites or something).
But i've seen some weird examples (You can see others source code below on the project) and it seems like they are adding much more to the models and also renaming the source/foreign_key/class_name.
Am I missing something? This still allows a user to "own" an event right? Maybe im mis-understanding how many-to-many works. But this fits at least in my mind of how it should be.
For reference some other models I was seeing was similar to this:
class Event < ActiveRecord::Base
belongs_to :creator, :class_name => "User"
has_many :event_attendees, :foreign_key => :attended_event_id
has_many :attendees, :through => :event_attendees
end
class EventAttendee < ActiveRecord::Base
belongs_to :attendee, :class_name => "User"
belongs_to :attended_event, :class_name => "Event"
end
class User < ActiveRecord::Base
has_many :created_events, :foreign_key => :creator_id, :class_name => "Event"
has_many :event_attendees, :foreign_key => :attendee_id
has_many :attended_events, :through => :event_attendees, :foreign_key => :attendee_id'
end
Basically similar things to the above. Im not really sure what this is doing? Or why all the extra is necessary.
In your example everything according to conventions. Maybe except many-to-many table naming.
attendances table has 'user_id' and 'event_id' fields. But in case it could conflict with other fields, or not descriptive enough you could use different keys.
belongs_to :creator, :class_name => "User"
belongs_to :creator by default would look for Creator model, so it is needed to specify class name explicitly, like in the provided example.
has_many :event_attendees, :foreign_key => :attended_event_id
By default foreign key would be event_id, so here it is specified explicitly too.
has_many :created_events, :foreign_key => :creator_id, :class_name => "Event"
By default, rails would look for user_id foreign key and CreatedEvent model. And these attributes specified explicitly.
You just need to understand what attributes rails provides by default, to change if it is required.
ActiveRecord associations default to a class and foreign key with the same name as the association. The code here is specifically specifying these because they are not the default.
Related
I'm trying to set up some new classes and associations in a Rails 2.2.2 app (please don't ask me to upgrade it).
The idea is that there is a Conversation class. It can have many participants, which are a mix of User and Pupil records, and it can have many owners, which can be a mix of a variety of things, including User and Pupil records. This is what I have so far:
#the :owner association can point to *anything*, including a Pupil or User record
class ConversationOwnership < ActiveRecord::Base
belongs_to :conversation
belongs_to :owner, :polymorphic => true
end
#the :participant association will point to either a Pupil or User record
class ConversationParticipant < ActiveRecord::Base
belongs_to :conversation
belongs_to :participant, :polymorphic => true
end
class Conversation < ActiveRecord::Base
has_many :conversation_ownerships
has_many :owners, :through => :conversation_ownerships
has_many :conversation_participants
has_many :participants, :through => :conversation_participants
end
This currently isn't working:
Conversation.first.participants
=> ActiveRecord::HasManyThroughAssociationPolymorphicError: Cannot have a has_many :through association 'Conversation#participants' on the polymorphic object 'Participant#participant'.
Now, I know that the has_many_polymorphs plugin was designed to solve this very problem, but the problem with using that is that it automatically makes associations for each of the listed classes, and because User and Pupil are in both participants and owners, they would clash:
OWNER_CLASSES = [:ilps, :lessons, :digilearning_modules, :resources, :pupil_groups, :pupils, :users]
PARTICIPANT_CLASSES = [:pupils, :users, :contacts, :parent_carers]
has_many_polymorphs :participants, :from => PARTICIPANT_CLASSES, :through => :conversation_participants, :order => "conversation_participants.created_at"
has_many_polymorphs :owners, :from => OWNER_CLASSES, :through => :conversation_ownerships, :order => "conversation_ownerships.owner_type, conversation_ownerships.created_at"
With this, the first hmp makes a .pupils association which effectively means "participants that are Pupils", and the second hmp also makes a .pupils association which effectively means "owners that are Pupils".
I don't want these extra associations that has_many_polymorphs brings, which is why i thought I would roll my own associations. But, I can't get past that Cannot have a has_many :through association 'Conversation#participants' on the polymorphic object 'Participant#participant'. error.
This feels like it should be possible - is it?
I have a Friends model with user_id and friend_id...both are id's back to specific users.
What I'd like to able to do is something like this:
#relationship = Friend.find_by_user_id(current_user.id)
#relationship.friend.username
Where I can basically pull the user through the friend_id column in the same way I can do #relationship.user.username.
How would I setup my associations to pull that off?
Isn't this just a many-to-many situation.
I think there is a perfect solution in Many-to-many relationship with the same model in rails?
Hope this help!
Use class_name if your column doesn't reflect the convention expected:
class Friendship < ActiveRecord::Base
belongs_to :user
belongs_to :friend, class_name: 'User'
end
Note that I modified the model name to Friendship to better reflect the use of this model. Also, you can make it easier for yourself if you revise your User model to look like this:
class User < ActiveRecord::Base
has_many :friendships
has_many :friends, :through => :friendships
has_many :friendships_of, :class_name => 'Friendship', :foreign_key => :friend_id
has_many :friends_of, :through => :friendships_of, :source => :user
end
Now to see all the user's friends:
current_user.friends.map(&:username)
And to see who has 'friended' the user:
current_user.friends_of.map(&:username)
I need some suggests for the model relationship that I'm going to develop:
I want to create a research table that keep track of all the reasearches performed inside the platform.
In the platform I'm developing, an user can search for other users.
In order to do it, I thought to create 3 fields in the research table: Performer (user_id that submit the research) Research_string (The string that the performer submit) and Results (that is one or more user).
Of course the relationship among user and research tables will be many to many, but note that the research table has 2 different column that involves the user_id (performer and results) so how can I specify to rails ? I thought something like that :
class User < ActiveRecord::Base
has_many :performed_research, :through => :research_table
class Research < ActiveRecord::Base
has_many :users
But how can I specify that the has_many users in the Research tables implies two different relations depending by the column ?
Tnx
EDITED: my solution
Your solution is not correct, because the user has only the research performed and not the research where he is resulted. I made another solution, that it's not the best of clear but it works, I would like to have your judge:
class Research < ActiveRecord::Base
belongs_to :searcher, :class_name => 'User', :foreign_key=> 'submitter_id'
has_many :found_users, :through=>:user_researches,:source=>:user
#It is necessary to let the association work without class_name it would look for
userResearch class
has_many :user_researches, :class_name =>'User_research'
end
class User_research < ActiveRecord::Base
belongs_to :user
belongs_to :research
end
class User < ActiveRecord::Base
# It returns a list of research performed by the user
has_many :researches, :foreign_key => 'submitter_id'
# It is necessary to let the searcher relationship works
has_many :user_researches, :class_name =>'User_research'
#==> Searcher will return an Array of research where the user's skill has been researched
has_many :follower_researches, :through => :user_researches, :source=>:research
end
I say that it;s not the best because the follower_research of the user model, show an array of research when he has been results ... and not an Array of submitter that searching him, so to obtain them, I have to scroll the array of research and then take the searcher field ... Are you able to perform an improvement (hopefully less complex than this)
Do you mean something like this?
class User < ActiveRecord::Base
has_many :research_entries
class ResearchEntry < ActiveRecord::Base
has_one :performer, :class_name => 'User'
has_and_belongs_to_many :resulting_users, :class_name => 'User'
Update: I changed this to use the has_and_belongs_to_many relationship which will allow you to use a join table to connect many users into "resulting_users" field of the ResearchEntry
Something like this:
class User < ActiveRecord::Base
has_many :submitted_researches, :class_name => 'Research', :foreign_key => 'submitter_id'
has_manu :researches, :through => :performed_researches
class Research < ActiveRecord::Base
belongs_to :submitter, :class_name => 'User'
has_many :researchers, :through => :performed_researches, :class_name => 'User'
class PerformedResearch < ActiveRecord::Base
belongs_to :user
belongs_to :research
See: http://guides.rubyonrails.org/association_basics.html#the-has_many-through-association
Update: I think I misread something. What is results? and how is it related to users?
Update 2: Still not sure I understand but here's another stab
I originally thought you were doing something related to academic research and the Research model was for research papers with the performer being scientists that did the research.
From re-reading your question I'm now thinking you have a rails application with some users and a search feature that lets a user search for other users and for each search you are trying to keep track of which user did the search and which users they found.
Let me know if any of these assumptions are wrong.
Based on that:
class User < ActiveRecord::Base
has_many :searches #all the searches this user performed
class Search < ActiveRecord::Base
belongs_to :searcher, :class_name => 'User' # the user who performed the search
has_many :found_users, :though => :user_search_results, :foreign_key => 'user_id' # using foreign_key because I want to change the name to 'found_users'
#alternatively if you don't want to use foreign_key use the line bellow instead
#has_many :users, :thorough => :user_search_results
class UserSearchResult < ActiveRecord::Base
belongs_to :user
belongs_to :search
I'm struggling with a has_many association. I have a diary application. The model players are as follows:
User
UserFriend
UserFoodProfile
I want to be able to get at all the foods that a user's friends have eaten. So, I want to be able to get: current_user.friends.profiles
I've setup the associations properly so far so that I'm able to access current_user.friends, but now I want to be able to get all the friend's entries as well over the last 30 days.
Here are my models
class User < ActiveRecord::Base
cattr_reader :per_page
##per_page = 20
has_many :user_food_profiles
has_many :preferred_profiles
has_many :food_profiles, :through => :user_food_profiles
has_many :weight_entries
has_one :notification
has_many :user_friends
has_many :friendships, :class_name => "UserFriend", :foreign_key => "friend_id"
has_many :friends, :through => :user_friends
class UserFriend < ActiveRecord::Base
belongs_to :user
belongs_to :friend, :class_name => "User", :foreign_key => "friend_id"
class UserFoodProfile < ActiveRecord::Base
belongs_to :user
belongs_to :food_profile
belongs_to :post
The UserFriend model is setup the following way:
id
user_id
friend_id
friend_name
I want to connect to user_food_profiles from friend so that I can get a user's friend's current user_food_profiles as "entries" but everything I've tried hasn't worked. How would I setup this association?
Tried to do:
UserFriend: has_many :user_food_profiles, :as => 'entries'
UserFoodProfile: belongs_to :friend, :foreign_key => 'friend_id'
Any ideas on how to make this work? Tempted to create a custom finder_sql but I'm sure this can work with associations.
Isn't a "friend" just another user that's in the database?
Let your UserFriend be a many_to_many relationship (either with "has_and_belongs_to_many" or "has_many :through"): each user can have several users as friends.
You can then link those user_ids (which could be in the many_to_many table called 'friend_id' if you like) to their foodprofile without a problem, since it is using the same link as user.foodprofile .
This is the line I see being the problem:
class User < ActiveRecord::Base
# <snip/>
has_many :friendships,
:class_name => "UserFriend",
:foreign_key => "friend_id"
I'm assuming that you're using a join table here called user_friend. That would mean that the foreign key there should be "user_id".
Now, unless you're going to store extra metadata in that UserFriend model, it's not required — you can get away with a self-referential has_and_belongs_to_many relationship like so:
has_and_belongs_to_many :friends,
:class_name => "User",
:join_table => "user_friends",
:foreign_key => "user_id",
:association_foreign_key => "friend_id"
Doing this, all you have to do is user.friends.profiles quite easily.
Now, if the relationship is bi-directional it gets a bit more complex, but I feel like this should at least get you started along the way.
I run the risk of palm-to-forehead here, but I can't quite figure out how to do this with Rails' ActiveRecord sugar.
I have a tickets table that has two columns (submitter_id and assignee_id) that should each reference a different user from the users table (specifically the id column in the users table). I'd like to be able to do things like ticket.submitter.name and ticket.assignee.email using ActiveRecord's associations. Submitter and Assignee are simply user objects under different associative names.
The only thing I've found that comes close to what I am doing is using polymorphic associations, but in the end I'm fairly certain that it's not really what I need. I'm not going to have multiple types, both submitter and assignee will be users, and very well could be two different users.
Any help would be fantastic. Thanks!
class Ticket < ActiveRecord::Base
belongs_to :submitter, :class_name => "User"
belongs_to :assignee, :class_name => "User"
end
Should work.
Edit: Without trying it out, I'm not sure whether you need the :foreign_key parameter or not. My instinct is not, but it couldn't hurt.
Edit again: Sorry, left off the User -> Ticket associations. You didn't mention using them, and I typically will only add associations in one direction if I don't plan on using them in the other direction.
Anyway, try:
class User < ActiveRecord::Base
has_many :assigned_tickets, :class_name => "Ticket", :foreign_key => "assignee_id"
has_many :submitted_tickets, :class_name => "Ticket", :foreign_key => "submitter_id"
end
Something like this should work
class Ticket < ActiveRecord::Base
belongs_to :submitter, :class_name => 'User', :foreign_key => 'submitter_id'
belongs_to :assignee, :class_name => 'User', :foreign_key => 'assignee_id'
end
class User < ActiveRecord::Base
has_many :tickets, :class_name => 'Ticket', :foreign_key => 'submitter_id'
has_many :tickets_assigned, :class_name => 'Ticket', :foreign_key => 'assignee_id'
end
Yes, PreciousBodilyFluids is right we don't need to specify the foreign_key in the Ticket class as rails can infer it from the column name, i.e. submitter_id and assignee_id
But if your association name is different from the column_name_{id} then you will have to specify it, i.e. the User class case