Not sure which association best fits what I want. Basically it's a todo list. The list is a task and that task has many users.
ie: Dig a hole and plant some seeds. Digging a hole will require two or more people. Jim and Jo are digging the hole and Jo will plant the seeds after. So two lists to complete, the first by two users and the other by one. Both user can complete both lists if needed.
Todo: has many lists
List: belongs to todo
List: has many users
User: has many lists
If Im not clear, each task (list) on a todo can be completed by any user. I struggle to see where to put a list_id on the users table. That's not possible as that user can be doing another (list) at the same time. Im not sure how through: :association comes into play here.
User.first.lists #= []
Todo.first.lists.first.users #= []
I get nothing as the user_id needs to go somewhere.
If I'm not mistaken it sounds like you need a join table. you then state that your records have a relation :through the join table.
Example
you have a join table called: user_lists which will contain 3 pieces of data (id, user_id, list_id)
so each time a user has a list you create a record on this table.
Then in your User model
class User < ActiveRecord::Base
has_many :lists, :through => :user_lists
end
If I have understood your setup correctly then I hope this helps, if not let me know.
You can read more about associations here http://guides.rubyonrails.org/association_basics.html
Related
I have three models with the following associations:
User has_many :owns, has_many :owned_books, :through => :owns, source: :book
Book has_many :owns
Own belongs_to :user, :counter_cache => true, belongs_to :book
I also have a page that tracks the top users by owns with the following query:
User.all.order('owns_count desc').limit(25)
I would now like to add a new page which can track top users by owns as above, but with a condition:
Book.where(:publisher => "Publisher #1")
What would be the most efficient way to do this?
I'm interesting if there is something special for this case, but my shot would be the following.
First, I don't see how polymorphic association can be applied here. You have just one object (user) that book can belong to. As I understand, polymorphic is for connecting book to several dif. objects (e.g. to User, Library, Shelf, etc.) (edit - initial text of question mentioned polymorphic associations, now it doesn't)
Second, I don't believe there is a way to cache counters here, as long as "Publisher #1" is a varying input parameter, and not a set of few pre-defined and known publishers (few constants).
Third, I would assume that amount of books by single Publisher is relatively limited. So even if you have millions of books in your table, amount of books per publisher should be hundreds maximum.
Then you can first query for all Publisher's books ids, e.g.
book_ids = Book.where(:publisher => "Publisher #1").pluck(:id)
And then query in owns table for top users ids:
Owns.select("user_id, book_id, count(book_id) as total_owns").where(book_id: book_ids).group(:user_id).order(total_owns: :desc).limit(25)
Disclaimer - I didn't try the statement in rails console, as I don't have your objects defined. I'm basing on group call in ActiveRecord docs
Edit. In order to make things more efficient, you can try the following:
0) Just in case, ensure you have indexes on Owns table for both foreign keys.
1) Use pluck for the second query as well not to create Own objects, although should not be a big difference because of limit(25). Something like this:
users_ids = Owns.where(book_id: book_ids).group(:user_id).order("count(*) DESC").limit(25).pluck("user_id")
See this question for reference.
2) Load all result users in one subsequent query and not N queries for each user
top_users = User.where(:id => users_ids)
3) Try joining User table in the first order:
owns_res = Owns.includes(:user).select("user_id, book_id, count(book_id) as total_owns").where(book_id: book_ids).group(:user_id).order("total_owns DESC").limit(25)
And then use owns_res.first.user
In my ruby on rails app i have two models: User and Item
In my user model I would like a relation where a user can have many items like this:
has_many :items
For the relationship I would not only use the user_id column in the items table.
When I do
User.includes(:items)
I would rather have all items where
- the items user_id belongs to the user (the classical way)
- or e.g. a boolean column (like all_users) is true
Can this be done with
has_many :items + any special options?
And how would it look like?
Thanks & Regards, Andreas
User.includes(:items) just instructs rails SQL builder to load all nested items withing loaded users.
That said,
User.includes(:items).all # will load all users with all nested items
User.includes(:items).where(name: 'Joe') # will load user(s) Joe and their items
this is done to minimize an amount of queries against the database.
Whether one wants to load all items, the query on Item should be used, e.g.:
Item.where(user_id: User.find_by_name('Joe').pluck(:id))
So I have been trying to create a dummy application to try and learn Rails. The app I thought I could create is a coffee ordering app for a group of people in work.
So the website will have many users.
A user can create a coffee_order.
A coffee order contains orders for other individual users.
Each user can have one or more coffee_shop_items (e.g. latte,
cappuccino,danish, muffin, etc)
A coffee order also has an assignee, this is the person who is tasked
with going and getting the order.
So as a user, I create a coffee order, select an assignee, add users to the order, and add one or more coffee shop items to each user,
I am really struggling with how the database should be, and what the associations need to be, along with any join tables?
I am also trying to use nested attributes for the form entry.
Thanks in advance for help.
Update with some code I have tried to create a coffee order:
#coffee_order = CoffeeOrder.new(coffee_order_params)
params[:coffee_order][:user_coffee_orders_attributes].each do |user_order|
order = #coffee_order.user_coffee_orders.new(user_id: user_order[1][:user_id].to_i)
user_order[1][:coffee_shop_items].each do |item|
coffee_shop_item = CoffeeShopItems.find(item) if item != ""
# this line fails! see error below
#coffee_order.user_coffee_orders.coffee_shop_items << coffee_shop_item if coffee_shop_item != nil
end
end
error:
NoMethodError (undefined method `coffee_shop_items' for #<UserCoffeeOrder::ActiveRecord_Associations_CollectionProxy:0x42c6180>):
The coffee_shop_items belong to the order, not the user. After all, a user could probably create another order another day? You should probably also check out the rails documentation, which, IIRC actually contains a walk-through of a shopping cart application.
User has_many :coffes_orders
User has_many :coffee_orders_he_needs_to_get, class_name: "CoffeeOrder", foreign_key: "assignee_id"
CoffeeOrder belongs_to :user
CoffeeOrder belongs_to :assignee, class_name: "User"
CoffeeOrder has_and_belongs_to_many :coffee_shop_items
Coffee_shop_items has_and_belongs_to_many :coffee_orders
I have groups (Group model) in my app, which represent groups of people.
I want each group to have its own forum.
Should I just have the forum id in the groups table? It doesn't feel right. If I did it myself, the forum would have a polymorphic association to a "forumable" element (groups in this case, but I have other models that would need a forum).
Any opinions on what I should do? Modify the gem to fit my needs, or just have the forum_id in my models that need a forum? Or another solution maybe?
I'm the guy who started Forem (its the volunteers who did most of the hard work, though!), I think I can answer this question.
If you want only certain groups to have access to one and only one forum then you can put the forum_id field on the groups table and do it that way. What you can do then is override the can_read_forem_forum? method in your User model to perform a permission check for that user:
def can_read_forem_forum?(forum)
groups.where(:forum_id => forum.id).any?
end
This is used in Forem's ability model to determine whether or not a person can access a forum. What this method is going to do is that it will only return groups for that user that have link that specific forum. If there are any, then it's known that the user can access that forum.
Now if you're going the other route where a group may have access to many forums, well then you'd define a joins table between groups and forem_forums (called forum_groups) and define it as an association in your Group model like this:
has_many :forum_groups
has_many :forums, :through => :forum_groups, :class_name => "Forem::Forum"
You would need to also define a new model inside your application for this forum_groups association, it would be called ForumGroup and go a little like this:
class ForumGroup < ActiveRecord::Base
belongs_to :forum, :class_name => "Forem::Forum"
belongs_to :group
end
We're doing it this way so you have an easy way to manage the associations between forums and groups. If you did has_and_belongs_to_many, it generally only provides a gigantic pain in the ass when you want to delete one specific record from that join table.
Now, with that all nicely set up, the method you want to define in your User model is this one:
def can_read_forem_forum?(forum)
groups.joins(:forums).where("forem_forums.id = ?", forum.id).any?
end
Same thing, except this time we find all the groups that are linked to a specific forum through that association we set up earlier. This will do an INNER JOIN on the forum_groups table, and then another on the forem_forums table, getting the data required.
I hope this helps you, and thanks for using Forem!
I am starting to create my sites in Ruby on Rails these days instead of PHP.
I have picked up the language easily but still not 100% confident with associations :)
I have this situation:
User Model
has_and_belongs_to_many :roles
Roles Model
has_and_belongs_to_many :users
Journal Model
has_and_belongs_to_many :roles
So I have a roles_users table and a journals_roles table
I can access the user roles like so:
user = User.find(1)
User.roles
This gives me the roles assigned to the user, I can then access the journal model like so:
journals = user.roles.first.journals
This gets me the journals associated with the user based on the roles. I want to be able to access the journals like so user.journals
In my user model I have tried this:
def journals
self.roles.collect { |role| role.journals }.flatten
end
This gets me the journals in a flatten array but unfortunately I am unable to access anything associated with journals in this case, e.g in the journals model it has:
has_many :items
When I try to access user.journals.items it does not work as it is a flatten array which I am trying to access the has_many association.
Is it possible to get the user.journals another way other than the way I have shown above with the collect method?
Hope you guys understand what I mean, if not let me know and ill try to explain it better.
Cheers
Eef
If you want to have user.journals you should write query by hand. As far as I know Rails does has_many :through associations (habtm is a kind of has_many :through) one level deep. You can use has_many with finder_sql.
user.journals.items in your example doesn't work, becouse journals is an array and it doesn't have items method associated. So, you need to select one journal and then call items:
user.journals.first.items
I would also modify your journals method:
def journals
self.roles(:include => :journals).collect { |role| role.journals }.flatten.uniq
end
uniq removes duplicates and :inlcude => :journals should improve sql queries.
Similar question https://stackoverflow.com/questions/2802539/ruby-on-rails-join-table-associations
You can use Journal.scoped to create scope with conditions you need. As you have many-to-many association for journals-roles, you need to access joining table either with separate query or with inner select:
def journals
Journal.scoped(:conditions => ["journals.id in (Select journal_id from journals_roles where role_id in (?))", role_ids])
end
Then you can use user.journals.all(:include => :items) etc