Intersection of two relations

Question

Say I have two relations that hold records in the same model, such as:

@companies1 = Company.where(...)
@companies2 = Company.where(...)

Ho

Answer 1

For anyone who is stuck with Rails4 and cant use Rails5 .or syntax:

I had a dynamically number of big queries, which had similar conditions ( and therefore also similar results). My rake server would have problems when all of them at once would get instantiated, converted to arrays and then merged.

I needed a ActiveRecord::Relation (not fired yet) to use with find_each.

Looked something like this:

Class Conditions
  def initialize
    self.where_arr = []
    self.joins_arr = []
  end

  def my_condition1
    where_arr << 'customers.status = "active"'
    joins_arr << :customer
  end

  def my_condition2
    where_arr << 'companies.id = 1'
  end
end

conditions = []    
joins = []
# probably call them in a .each block with .send
conditions1 = Conditions.new
conditions1.my_condition1
conditions1.my_condition2
conditions << "(#{conditions1.where_arr.join(' AND ')})"
joins << conditions1.joins_arr

conditions2 = Conditions.new
conditions2.my_condition1
joins << conditions2.joins_arr

Company.joins(joins).where(conditions.join(' OR '))

=> SELECT companies.* FROM companies 
INNER JOIN customers ON companies.customer_id = customers.id 
WHERE (customers.status = 'active' AND companies.id = 1) OR
(customers.status = 'active')

Its kind of hacky but it works, until you can hopefully migrate to Rails 5