I have the following models:
class Epic < ActiveRecord::Base
has_many :planograms
has_and_belongs_to_many :users
end
class Planogram < ActiveRecord::Base
belongs_to :epic
end
class User < ActiveRecord::Base
has_and_belongs_to_many :epics
end
There's also an epics_users table.
I can't figure out how to write an ActiveRecord query to get all Planograms for a specific user. I tried the following:
Planogram.joins(:epic).where(:epics_users => {:user_id => 1})
and many other combinations but I'm not that experienced in ActiveRecord queries.
You can relate users and planograms like this:
class User < ActiveRecord::Base
has_and_belongs_to_many :epics
has_many :planograms, :through => :epics
end
And get planograms of a particular user:
user.planograms
In this case, the relation with User is through Epic. You can try this:
Planogram.joins(epic: :users).where(:epics_users => {:user_id => 1})
You can read more for ActiveRecord's joins method here: http://guides.rubyonrails.org/active_record_querying.html#joining-tables
I would simply use Arel. First get the arel tables of your models by doing the following:
planograms = Planogram.arel_table
epics = Epic.arel_table
then create your query as the following:
Planogram.joins(:epic).where(epics[:user_id].eq(USER_ID))
Related
Setup
For this question, I'll use the following three classes:
class SolarSystem < ActiveRecord::Base
has_many :planets
scope :has_earthlike_planet, joins(:planets).merge(Planet.like_earth)
end
class Planet < ActiveRecord::Base
belongs_to :solar_system
belongs_to :planet_type
scope :like_earth, joins(:planet_type).where(:planet_types => {:life => true, :gravity => 9.8})
end
class PlanetType < ActiveRecord::Base
has_many :planets
attr_accessible :gravity, :life
end
Problem
The scope has_earthlike_planet does not work. It gives me the following error:
ActiveRecord::ConfigurationError: Association named 'planet_type' was
not found; perhaps you misspelled it?
Question
I have found out that this is because it is equivalent to the following:
joins(:planets, :planet_type)...
and SolarSystem does not have a planet_type association. I'd like to use the like_earth scope on Planet, the has_earthlike_planet on SolarSystem, and would like to avoid duplicating code and conditions. Is there a way to merge these scopes like I'm attempting to do but am missing a piece? If not, what other techniques can I use to accomplish these goals?
Apparently, at this time you can only merge simple constructs that don't involve joins. Here is a possible workaround if you modify your models to look like this:
class SolarSystem < ActiveRecord::Base
has_many :planets
has_many :planet_types, :through => :planets
scope :has_earthlike_planet, joins(:planet_types).merge(PlanetType.like_earth)
end
class Planet < ActiveRecord::Base
belongs_to :solar_system
belongs_to :planet_type
scope :like_earth, joins(:planet_type).merge(PlanetType.like_earth)
end
class PlanetType < ActiveRecord::Base
has_many :planets
attr_accessible :gravity, :life
scope :like_earth, where(:life => true, :gravity => 9.8)
end
** UPDATE **
For the record, a bug was filed about this behavior - hopefully will be fixed soon...
You are reusing the conditions from the scope Planet.like_earth, which joins planet_type. When these conditions are merged, the planet_type association is being called on SolarSystem, which doesn't exist.
A SolarSystem has many planet_types through planets, but this is still not the right association name, since it is pluralized. You can add the following to the SolarSystem class to setup the planet_type association, which is just an alias for planet_types. You can't use the Ruby alias however since AREL reflects on the association macros, and doesn't query on whether the model responds to a method by that name:
class SolarSystem < ActiveRecord::Base
has_many :planets
has_many :planet_types, :through => :planets
has_many :planet_type, :through => :planets, :class_name => 'PlanetType'
scope :has_earthlike_planet, joins(:planets).merge(Planet.like_earth)
end
SolarSystem.has_earthlike_planet.to_sql # => SELECT "solar_systems".* FROM "solar_systems" INNER JOIN "planets" ON "planets"."solar_system_id" = "solar_systems"."id" INNER JOIN "planets" "planet_types_solar_systems_join" ON "solar_systems"."id" = "planet_types_solar_systems_join"."solar_system_id" INNER JOIN "planet_types" ON "planet_types"."id" = "planet_types_solar_systems_join"."planet_type_id" WHERE "planet_types"."life" = 't' AND "planet_types"."gravity" = 9.8
An easy solution that I found is that you can change your joins in your Planet class to
joins(Planet.joins(:planet_type).join_sql)
This will create an SQL string for the joins which will always include the correct table names and therefore should always be working no matter if you call the scope directly or use it in a merge. It's not that nice looking and may be a bit of a hack, but it's only a little more code and there's no need to change your associations.
I have a simple Customer model with a has many relationship with a Purchase model.
class Customer < ActiveRecord::Base
has_many :purchases
end
I am repeatedly finding that I need to order Customer.purchases in my views in the following way:
#customer.purchases.joins(:shop).order("shops.position").order(:position) #yes, two orders chained
In the interest of keeping things DRY, I'd like to put this somewhere centralized so I don't have to repeatedly do it. Ideally, I'd like to make it the default ordering for Customer.purchases. For example:
class Customer < ActiveRecord::Base
has_many :purchases, :order => joins(:shop).order("shops.position").order(:position)
end
Obviously the above doesn't work. How should I do this?
In your customer model you specified joins(:shop) is the value for the key :order. I think here is the problem, So you can use the joins as a key instead of order like below,
class Customer < ActiveRecord::Base
has_many :purchases, :joins => [:shop], :order => "shops.position"
end
I think it may work.
In your purchases model, you can create a class method:
Purchase.rb:
def self.order_by_position
joins(:shop).order("shops.position").order(:position)
end
Then you can say things like:
#customer.purchases.order_by_position
Purchase.order_by_position
You could create a method on Customer that returns ordered purchases:
class Customer < ActiveRecord::Base
has_many :purchases
def ordered_purchases
purchases.joins(:shop).order("shops.position").order(:position)
end
end
and call #customer.ordered_purchases from your views.
i have 3 models like :
location, user, discovered_location(location_id,user_id)
I think i need an outer join in order to get all locations, as well as include the discovered_location model, if that location has been discovered by the user.
I would need something like {location1, location2, location3:includes discovered_location, location4 ..}
Is there a Rails 3 way to do that ? If not, what is the best way ?
EDIT
I want to get the locations specified above, for a certain user. To better illustrate, it should be :
user {location1, location2, location3:includes discovered_location, location4 ..}
(A user has many discovered locations)
You can do an outer join in Rails only by using an SQL literal in the joins method:
joins("OUTER JOIN table2 on table2.column = table1.column")
joins makes an inner join, includes makes an outer join.
http://guides.rubyonrails.org/active_record_querying.html#specifying-conditions-on-eager-loaded-associations
You need to check that the user id in your discovered_locations table is either equal to the id of the user in question, or is null. This is easily accomplished with the meta_where gem. Given the following models:
class User < ActiveRecord::Base
has_many :discovered_locations
has_many :locations, :through => :discovered_locations
end
class Location < ActiveRecord::Base
has_many :discovered_locations
has_many :users, :through => :discovered_locations
end
class DiscoveredLocation < ActiveRecord::Base
belongs_to :user
belongs_to :location
end
Insert some dummy data, then execute a statement such as this:
Location.includes(:discovered_locations).where(
{:discovered_locations => {:user_id => User.first.id}} |
{:discovered_locations => {:user_id => nil}}
).each do |loc|
puts "#{loc.name} #{loc.discovered_locations.empty? ? 'not visited' : 'visited'}"
end
So Rails doesn't have support for :through associations through a habtm relationship. There are plugins out there that will add this in for Rails 2.x, but I'm using Rails 3 / Edge, and only need the association for one particular model. So I thought I'd stump it out myself with the beauty that is Arel.
First, the models:
class CardSet < ActiveRecord::Base
has_and_belongs_to_many :cards, :uniq => true
end
class Card < ActiveRecord::Base
has_and_belongs_to_many :card_sets, :uniq => true
has_many :learnings, :dependent => :destroy
end
class Learning < ActiveRecord::Base
belongs_to :card
end
I want to get all the learnings that belong to a particular card set, :through => cards.
This is what I have so far in my CardSet model:
def learnings
c = Table(Card.table_name)
l = Table(Learning.table_name)
j = Table(self.class.send(:join_table_name, Card.table_name, CardSet.table_name))
learning_sql = l.where(l[:card_id].eq(c[:id])).where(c[:id].eq(j[:card_id])).join(j).on(j[:card_set_id].eq(self.id)).to_sql
Learning.find_by_sql(learning_sql)
end
which gives me (damn, Arel is beautiful!):
SELECT `learnings`.`id`, `learnings`.`card_id`, `learnings`.`user_id`, `learnings`.`ef`, `learnings`.`times_seen`, `learnings`.`next_to_be_seen`, `learnings`.`interval`, `learnings`.`reps`, `learnings`.`created_at`, `learnings`.`updated_at`, `card_sets_cards`.`card_set_id`, `card_sets_cards`.`card_id` FROM `learnings` INNER JOIN `card_sets_cards` ON `card_sets_cards`.`card_set_id` = 1 WHERE `learnings`.`card_id` = `cards`.`id` AND `cards`.`id` = `card_sets_cards`.`card_id`
which is oh so close to what I'm aiming for - just needs to add in the cards table in the FROM part of the statement.
And there's my question: I've looked through the Arel source, and for the life of me I can't figure out how to add in another table.
As a sidenote, is there a better way to run the result from Arel (which usually returns an Arel::Relation, which I don't want) through ActiveRecord, other than rendering to sql and running the query with find_by_sql as I'm doing?
I'm not familiar with Arel, but won't it handle:
l.includes(:card)
This is easier than what I wrote above, after I learned how Rails encapsulates Arel so you don't need to build the query directly.
If you're trying to stub nested habtm in the CardSet model, a.k.a.:
has_many :learnings, :through => :cards
then you can use this to simulate the behaviour:
class CardSet < ActiveRecord::Base
has_and_belongs_to_many :cards, :uniq => true
def learnings
Learning.joins(:card).where(:cards => { :id => self.card_ids })
end
end
then a query like this will work:
CardSet.first.learnings
I have a many-to-many relationship set up through a join model. Essentially, I allow people to express interests in activities.
class Activity < ActiveRecord::Base
has_many :personal_interests
has_many :people, :through => :personal_interests
end
class Person < ActiveRecord::Base
has_many :personal_interests
has_many :activities, :through => :personal_interests
end
class PersonalInterest < ActiveRecord::Base
belongs_to :person
belongs_to :activity
end
I now want to find out: in which activities has a particular user not expressed interest? This must include activities that have other people interested as well as activities with exactly zero people interested.
A successful (but inefficent) method were two separate queries:
(Activity.all - this_person.interests).first
How can I neatly express this query in ActiveRecord? Is there a (reliable, well-kept) plugin that abstracts the queries?
I think the easiest way will be to just use an SQL where clause fragment via the :conditions parameter.
For example:
Activity.all(:conditions => ['not exists (select 1 from personal_interests where person_id = ? and activity_id = activities.id)', this_person.id])
Totally untested, and probably doesn't work exactly right, but you get the idea.