CODEWITHSUNDEEP
ruby-on-railsruby-on-rails-3ruby-on-rails-4rails-activerecord
Prabhakaran
Prabhakaran

Reputation: 4013

rails active record to fetch result from multiple tables

I have the following query

SubCategory.joins(dropdown_heads: :dropdown_lists).where(id: params[:sub_cat_id])

The above query generates

SELECT "sub_categories".* FROM "sub_categories" INNER JOIN "dropdown_heads" ON "dropdown_heads"."sub_category_id" = "sub_categories"."id" INNER JOIN "dropdown_lists" ON "dropdown_lists"."dropdown_head_id" = "dropdown_heads"."id" WHERE "sub_categories"."id" = 6

But what I actually need is to fetch records from dropdown_heads and dropdown_lists only.

What modification do I need to achieve it?

Following are the associations

sub_category.rb

has_many: dropdown_heads

dropdown_head.rb

has_many: dropdown_lists
belongs_to: sub_category

dropdown_lists.rb

belongs_to: dropdown_head

Upvotes: 1

Views: 1301

Answers (3)

Deepak Kabbur
Deepak Kabbur

Reputation: 802

You can use 

SubCategory.joins(dropdown_heads: :dropdown_lists).where(id: params[:sub_cat_id].select("dropdown_heads.dropdown_heads, dropdown_lists.dropdown_lists")

Even you can use pluck() method of rails to retrieve specific fields.

Upvotes: 0

nickcen
nickcen

Reputation: 1692

You don't have to get the sub_category instance, you can just call

    dropdown_heads = DropdownHead.find_all_by_sub_category_id(params[:sub_cat_id])

and the remaining are just the same as @rb512 said.

Upvotes: 0

rb512
rb512

Reputation: 6948

Retrieve the sub_category record from the database

@sub_category = SubCategory.find(params[:sub_cat_id])

Retrieve all dropdown_heads

sub_category.dropdown_heads

Iterate through dropdown_head to retrieve dropdown_lists

@sub_category.dropdown_heads {|dropdown_head| dropdown_head.dropdown_lists} #do whatever you want with dropdown_lists

which is same as:

@sub_category.dropdown_heads.each |dropdown_head|
 dropdown_head.dropdown_lists
end

Upvotes: 1

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