My User table is connected to Company via a user_company table. Now I want to retrieve the company name that user belongs to. Please can you suggest the query I should use?
User
has_many :companies, :through => :user_companies
Company
has_many :users, :through => :user_companies
User does not directly belong to company.
user.company.name gives an error. I want to find out the company name which the user belongs to.
Since a user has multiple companies, it is user.companies. To get the names, you could do e.g. user.companies.map(&:name)
#user.companies will give you an array of all the companies that the user is associated with.
Now, you can simply iterate over the array and get the company's name for each of the companies.
company_names = []
#user.companies.each {|entry| company_names << entry.name}
This is when you don't have the company's name attribute in the user_companies table.
If you have it that way, you can simply get all the names by
UserCompany.where(:select=>"name", :user_id=> #user)
Related
I'm building a marketplace app. I have a Listing model (users list items to sell) and a User model. In the listing model, I have a userid column. And in the User model, I have a name field. In my listing show page, I want to display something like the below:
"Sold by #{#listing.user.name}"
But the join doesn't work in retrieving the name from the user table. If I change it to listing.userid then it works but I want to display the users name.
my user model has has_many :listings, dependent: :destroy
My listings model has belongs_to :user.
How can I display the user's name on the listing show page?
If you really have a column called userid instead of user_id then you have something very slightly different to what Rails expects... which is why Rails isn't finding it for you automatically.
Your best bet is to rename the column (using a migration) to user_id to take advantage of the Rails default behaviour. Trust me - it's worth the effort up front if you can do this.
If for some odd reason you can't (serious business constraints), then there are ways of telling rails that you are using a non-standard foreign-key... but lets not get to that unless you have to.
In SQL you can have SELECT x,y FROM ...
but if I use where, the sql generated will only select from the models which it is acting upon.
So for example:
user has_many :posts
post belongs_to :user
Post.includes(:users).where('created_at < ?' 1.day.ago) will have
SELECT "posts".* FROM "posts" WHERE (created_at > '2013-03-06 07:37:09.010916')
but how do I SELECT the post and the users so it will return the posts users as well?
UPDATE: As Saurabh pointed out, the loaded association should be :user and not :users
Includes is used to eager load association records, meaning that given the following
#posts = Post.includes(:user)
#posts.each do |post|
post.user
end
Only 2 queries will be made to the database, one for fetching the posts and another for fetching all the users that is associated to #posts. Rails manages the associations for you. Simple.
If you want to get a certain column value from a different table, try the following
#posts = Post.joins(:user).select('posts.*, users.name AS user_name')
#posts.first.user_name # will give you the name of the first user associated to the post
First, your associations are wrong. You can't do Post.includes(:users) when you say: post belongs_to :user.
The correct way is -
Post.includes(:user) for the belongs_to associations.
Second, you can select a value from different table by doing so:
Post.includes(:user).where(:user => {:name => params[:name]})
The above query will give you all the posts whose user name is params[:name] where :name is the field from the user table.
Working with Exported Data from API
I'm building a leaderboard that displays the Team.name of each team as well as the users who have picked that particular team as their favorites. I'm also populating another attribute Favorite.points; to display the users with the most points accumulated for that respective team.
Here are the models I'm working with:
Favorite.rb
class Favorite < ActiveRecord::Base
belongs_to :users
belongs_to :teams
end
Team.rb
class Team < ActiveRecord::Base
has_many :favorites
has_many :users, :through => :favorites
end
User.rb
class User < ActiveRecord::Base
has_many :favorites
has_many :teams, :through => :favorites
end
To start this process, I'm trying to match up the id's that are common between Team.external_id and Favorite.team_id (the same is the case for User.external_id => Favorites.user_id). I can use Team.find_all_by_external_id(3333) to get the IDs of all Team objects that have an external_id of '3333'and the same goes for Favorite.find_all_by_team_id.
What's the next best step for me to obtain/show the data I'm looking for? Is a SQL join clause best? Or is it better to write if statements matching up values and iterating through the JSON arrays?
Any help is appreciated, thanks!
This will get you all the favorites whose team_id matches the external_id attribute of a row in the teams table, for a specific team (here, the team with id 3333):
Favorite.joins("left outer join teams on teams.external_id = favorites.team_id")\
.where('team_id' => 3333)
The tricky thing here, as I mentioned in my comments, is that you are going entirely against the grain of rails associations when you match the external id on the Team model (an attribute which you have created) to the team_id on the Favorite model (which is used throughout rails to get and assign associations).
You will see the problem as soon as you try to actually get the team for the favorite you find in the above join:
f = Favorite.joins("left outer join teams on teams.external_id = favorites.team_id")\
.where('team_id' => 3333).first
=> #<Favorite id: 1, user_id: nil, team_id: 3333, points: nil, created_at: ... >
f.team
Team Load (0.3ms) SELECT "teams".* FROM "teams" WHERE "teams"."id" = 3333 LIMIT 1
=> nil
What's going on here? If you look closely at the query, you'll see that rails is selecting teams whose id is 3333. Note that it is not looking for teams whose external id is 3333, which is what you want.
The fundamental problem is that you are trying to use external ids (ids specific to your API) for associations, which won't work. And indeed, there is no reason to do it this way.
Instead, try this:
Favorite.joins(:team).where('teams.external_id = 3333')
This will get you all favorites whose teams have the external id 3333. Note that Rails will do this by joining on teams.id = favorites.team_id, then filtering by teams.external_id:
SELECT "favorites".* FROM "favorites" INNER JOIN "teams"
ON "teams"."id" = "favorites"."team_id" WHERE (teams.external_id = 3333)
You can do the same thing the other way around:
Team.joins(:favorites).where('teams.external_id = 3333')
which will generate the SQL:
SELECT "teams".* FROM "teams" INNER JOIN "favorites"
ON "favorites"."team_id" = "teams"."id" WHERE (teams.external_id = 3333)
Note again that it is the id that is being used in the join, not the external id. This is the right way to do this: use the conventional id for your associations, and then just filter wherever necessary by your (custom-defined, API-specific) external id.
Hope that helps!
UPDATE:
From the comments, it seems that the team_id on your Favorite model is being defined from the API data, which means that the id corresponds to the external_id of your Team model. This is a bad idea: in rails, the foreign key <model name>_id (team_id, user_id, etc.) has a specific meaning: the id is understood to map to the id field of the corresponding associated model (Team).
To get your associations to work, you need to use ids (not external ids) for associations everywhere (with your User model as well). To do this, you need to translate associations defined in the API to ids in the rails app. When you add a favorite from the API, find the Team id corresponding to the API team id.
external_team_id = ... # get external team id from API JSON data
favorite.team_id = Team.find_by_external_id(external_team_id).id
So you are assigning the id of the team with a given external id. You need to query the DB for each favorite you load from the API, which is potentially costly performance-wise, but since you only do it once it's not a big deal.
I'm running into problems when I move this SQL around to different database adapters. I want to convert it into something more flexible. Here it is:
Foo.includes([{ :group => :memberships }, :phone]).
where('("memberships"."user_id" = ? AND "memberships"."owner" = ?)
OR "phone"."user_id" = ?', user.id, true, user.id)
user is the current user (this query is within a CanCan ability file). The idea is to query all foo's where the current user is the owner of the foo's group, OR the foo's phone is owned by the current user.
I have tried many different queries, but I can't see to get the OR syntax right. Because this is in a CanCan ability, it is not possible to combine two queries, it all needs to be in one large scope like the one above. Is this possible to do?
Group membership is done through the join table memberships, the owner is designated with the owner field.
class Foo
belongs_to :group
belongs_to :phone
end
I've got a model called Users, some of whom are considered Authors. This is accomplished through a table called Roles, which lists a number of different roles: "Author" is one. A many-to-many association in a table called Permissions links Roles and Users.
To check whether a User has the Author permission, I have a method that runs through the Permissions linked to that particular User and returns whether any of them also links to the Author permission.
This system has served me well. However, it makes it clunky to search and order the Authors on the site. What I'd like to do is something simple and graceful, ideally like a named scope that will allow me to say things like Users.authors.order("date_joined") or something like that.
As it is right now, I don't have any way to get the group of "Author" users other than pulling all Users out of the database, running through them one at a time, searching for their Author permission, and then adding them to an array of Users if it is found.
This seems rather ungraceful, especially as I have to do it every time I want to present the list of Authors in a view.
Is there a better way?
EDIT -- Solution:
Following the helpful advice below and the tips from http://railscasts.com/episodes/215-advanced-queries-in-rails-3?view=asciicast I was able to put together the following.
In User.rb:
class User < ActiveRecord::Base
scope :authors, joins(:permissions) & Permission.author_permissions
scope :admins, joins(:permissions) & Permission.admin_permissions
In Permission.rb:
class Permission < ActiveRecord::Base
scope :author_permissions, where("role_id = ?", Role.find_by_rolename("author"))
scope :admin_permissions, where("role_id = ?", Role.find_by_rolename("administrator"))
And voila! Now I can call Users.authors and it works like a charm.
Keep the schema structure that you have but make sure to add the proper table indexes.
Then to query for users in specific roles you can do
User.all(:joins => :roles,
:conditions => {:roles => {:id => pick_a_role_id}})
have you looked at CanCan? It will probably require a little refactoring, mostly to create a current_user method. A guide to roles can be found here