从联接表Ruby on Rails中关联的表中汇总数据

Question

I would like to ask how am I going to get the sum of material quantity in join table on every lot within a block.

The requirementalizes table has "quantity" column within.

For example..

A Block has 3 lots, each lot is associated with requirement to have materials.
Each Lot has...
material x- 200
material y- 250

How will I sum up the quantity for every material to have for Block.
Block will have...
material x- 600
material y- 750

this is how my model association structured

class Block < ApplicationRecord
  has_many :lots
end

class Lot < ApplicationRecord
  belongs_to :block
  belongs_to :requirement
end

class Requirement < ApplicationRecord
  has_many :requirementalizes
  has_many :materials, through: :requirementalizes
  belongs_to :lot
end

class Requirementalize < ApplicationRecord
  belongs_to :requirement
  belongs_to :material
end

class Material < ApplicationRecord
  has_one :requirementalize
  has_many :requirements, through: :requirementalize
end

Any help would be appreciated.

Answer 1

You could use ActiveRecord::Calculations sum

Just a quick example, You get the associated record you are looking for and call @something.sum(:quantity)

Here is an example using rails console. Just to give an idea of what is going on.

2.3.3 :009 > total = Block.find(1).lots
...
#records found
...
2.3.3 :010 > total.sum(:quantity)
   (20.7ms)  SELECT SUM(`lots`.`quantity`) FROM `lots` WHERE `lots`.`block_id` = 1
 => 1205 #or some number

Reference: http://api.rubyonrails.org/classes/ActiveRecord/Calculations.html#method-i-sum

Answer 2

Thanks to Bryan Bibat. He helped me to solve this problem.

This is the solution to my problem.

Block.each do |block|
  materials = block.lots.joins(requirement: :materials).group("materials.name").sum(:quantity)
  @blocks << { Block: block.block_no, Materials: materials }
end