user.rb
has_many :properties property.rb
belongs_to :user I want to get a user who have min properties like wise for max also.
I cant find any query related to that
3 Answers
Answers 1
To find the user with min properties you can simply do,
User.joins(:properties).group("properties.user_id").order("count(properties.user_id) desc").last And to find the user with max properties,
User.joins(:properties).group("properties.user_id").order("count(properties.user_id) desc").first Note: Because its a join operation with properties, so user with no properties will not appear in this query.
Answers 2
You could use counter_cache.
The :counter_cache option can be used to make finding the number of belonging objects more efficient.
From here
belongs_to :user, counter_cache: true Then create the migration:
def self.up add_column :users, :properties_count, :integer, :default => 0 User.reset_column_information User.find(:all).each do |u| User.update_counters u.id, :properties_count => u.properties.length end end Then you can fetch user which have max properties_count
User.maximum("properties_count") Here is an awesome RailsCast about counter_cache
Answers 3
I think you can do like this by scopes
class User has_many :properties scope :max_properties, select("users.id, count(properties.id) AS properties_count"). joins(:properties). group("properties.id"). order("properties_count DESC"). limit(1) scope :min_properties, select("users.id, count(properties.id) AS properties_count"). joins(:properties). group("properties.id"). order("properties_count ASC"). limit(1) And just call User.max_properties and User.min_properties
UPDATED:
It will aslo work like BoraMa suggeted
class User has_many :properties scope :max_properties, select("users.*, count(properties.id) AS properties_count"). joins(:properties). group("users.id"). order("properties_count DESC"). limit(1) scope :min_properties, select("users.*, count(properties.id) AS properties_count"). joins(:properties). group("users.id"). order("properties_count ASC"). limit(1) 
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