Select distinct including a value from a different model/table - sql

Question

I have 2 models/tables:
class CollectionPoint < ActiveRecord::Base
belongs_to :collection_type
...
class CollectionType < ActiveRecord::Base
has_many :collection_points
...
Every CollectionPoint has a city (column)
Every CollectionType has a name (column)
I would like to get all the distinct collection type names in each city in order to show a directory like this in my view:
city A
collection_type.name A
collection_type.name B
collection_type.name C
...
city B
collection_type.name A
collection_type.name B
collection_type.name C
...
city C
collection_type.name A
collection_type.name B
collection_type.name C
...
...
The best thing would be an array that is grouped by cities so that i could go like this in my view:
#cities.each do |city|
...
city.each do |collection_type_name|
...
end
end
So i tried this:
CollectionPoint.select("DISTINCT city, collection_type_id")
But then i get only the collection type ids, not the collection type names. Also i don't need the collection point ids (which are nil in the query result anyway), so i tried this:
CollectionPoint.includes(:collection_type).select("DISTINCT city, collection_types.name").references(:collection_types)
But this is not getting me anywhere neither.
I'm quite frustrated because i know there must be a solution to this i don't have a clue about. Maybe you could help me?
Cheers
Solution A
The simplest solution to this problem was adding this line of code to my controller:
#cities = CollectionPoint.includes(:collection_type).select("DISTINCT city, collection_type_id").order(:city).group_by(&:city)
So i could show the results in my view accordingly:
- #cities.each do |city, collection_points|
%h2
= city
= content_tag :ul, title: "... " + city do
%li
= link_to "... " + city, "/.../" + city
- collection_points.each do |cp|
%li
= link_to cp.collection_type.name + " in " + city, "/" + cp.collection_type.name + "/" + city
Solution B
I guess the best solution is to create a separate City model and rework your assosiations:
class City < ActiveRecord::Base
has_many :collection_points
has_many :collection_types, through: :collection_points
...
class CollectionPoint < ActiveRecord::Base
belongs_to :collection_type
belongs_to :city
...
class CollectionType < ActiveRecord::Base
has_many :collection_points
has_many :cities, through: :collection_points
...
Then you can do all kinds of stuff, for example finding all collection types in a specific city:
City.where(name: "Cologne").first.collection_types
To list all distinct collection types in all distinct cities, the controller action looks like this:
#cities = City.includes(:collection_types).distinct
And in the view you can go like:
#cities.each do |city|
city.name
city.collection_types.each do |collection_type|
collection_type.name
end
end
More information on this can be found here:
Rails Model Assosiations
Thanks for your help, guys!

Answer 1

Do your CollectionName and CollectionType models have and belongs to many records? If so, this is the set up I would advise with:
Collector.rb
class Collector < ActiveRecord::Base
attr_accessible :collection_point_id, :collection_type_id
belongs_to :collection_point
belongs_to :collection_type
end
CollectionPoint.rb
class CollectionPoint < ActiveRecord::Base
attr_accessible :city
has_many :collectors
has_many :collection_types, :through => :collectors
end
CollectionType.rb
class CollectionType < ActiveRecord::Base
attr_accessible :name
has_many :collectors
has_many :collection_points, :through => :collectors
end
Then you can utilise the new ActiveRecord association and select distinct records with the group method:
#cities = CollectionPoint.select("DISTINCT(CITY)").all
Then print the #cities object with an each do method.
#cities.each do |city|
...
city.collection_types.each do |collection_type_name|
...
end
end

Answer 2

what about using active record -
grouped_by_city = CollectionPoint.all.group_by { |cp| cp.city }
would return
{ :city =>{stuff in here}}
and then you could do this:
- grouped_by_city.each do |city, info|
%p= city
%ul
%li= info.collection_type.name #not sure what this should be? depends on your models
if you play around with that a bit I think it will work for you. irb is your best friend!