In my application one can find all team reportees of an employee by doing the following
User.where(primary_reporter: "some unique code of a user")
where primary reporter is the user whose team reportees one needs to fetch.
However I am trying to now recursively find the reportees of the said user and the reportees of his team members forming a hierarchical chart. Have not been able to find anything there.
My user model is this:
class User
has_many :reportees, lambda { |user| includes(:actor).where [" .
(users.status = 1)"] }, class_name: 'User', foreign_key:
'primary_reporter'
end
class Actor
has_one: user
end
I am using postgres for the database
If you want to implement hierarchical implementation in postgres with rails then you can try ltree extension in postgres where you can make use of indexes (for fasten querying) as well. Also we have ruby gem, using this gem we can easily make queries.
References
Postgres: https://www.postgresql.org/docs/9.1/ltree.html
Rails: https://github.com/cfabianski/ltree_hierarchy
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.
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
SCENARIO
I have a table full of posts with a users table.
I want to be able to fetch all the posts and group them by users but I want to set a limit of say 10 per user.
class Post < ActiveRecord::Base
belongs_to :user
end
class User < ActiveRecord::Base
has_many :posts
end
# I thought this might work but it just grabs the first 10 posts and groups them
Post.find(:all, :limit=>10).group_by(&:user)
Any thoughts? Do I have to write custom SQL for or can Active Record do this?
Something like?
Post.group(:user_id).limit(10)
Post.group(:user_id).limit(10)
group_by is not a query method, but rather a method of Enumerable.
In your code, Post.find(:all, :limit => 10) is turned into an Array before being passed to group_by. The method above chains query methods together and only converts them to an Array when you need to use them.
ActiveRecord handles the whole thing. The above method translates to
SELECT `posts`.* FROM `posts` GROUP BY user_id LIMIT 10
The only way I know to grab the recent 10 posts per user would require a nested sub-query (which can have performance issues) or postgres-style lateral join. Fairly confident this cannot be accomplished with only active-record and requires writing custom SQL, which you've indicated you want to avoid.
As an alternative that could be accomplished without custom SQL, you could list each user and their posts within a time window (e.g. past month or year) with the following:
class User < ActiveRecord::Base
has_many :recent_posts, -> { where(posts: {created_at 1.month.ago..Time.now}) }, class_name: 'Post'
end
User.includes(:recent_posts).each do |user|
user.recent_posts
end
Which would not execute a SQL query for each user and would therefore be relatively performant compared with doing it purely in ruby.