Querying associated records using Active Record - ruby-on-rails

Question

I have a model Tippani, which belongs to another model Fiscal Year.
Tippani.rb
class QuotationTippani < ApplicationRecord
belongs_to :fiscal_year
end
I have two instances of tippani class, that belong to the same fiscal year.
I want to get the instances of tippani class that belongs to the same fiscal year.
I tried something like this:
Tippani.where(fiscal_year_id == 4)
But I get an error
undefined local variable or method `fiscal_year_id' for main:Object
Also, is there some query method, where I could get all the tippani instances, whose fiscal year is less than 2073 or some number.
Something like this:
Tippani.fiscal_year.where(year < 2074)

Answer 1

You need to pass Hash into your query method, like this:
QuotationTippani.where(fiscal_year_id: 4)
or, if you have FiscalYear instance available and Fiscalyear#quotation_tippanies association is set up:
fiscal_year.quotation_tippanies
About the filtering by year, it's about using joins and passing parameters properly:
QuotationTippani.joins(:fiscal_year).where('fiscal_years.year < ?', 2074)
Generally speaking, I advice you to read this guide:
https://guides.rubyonrails.org/active_record_querying.html
You'll find all the information you need here.

Answer 2

== is the comparison operator. When you write:
Tippani.where(fiscal_year_id == 4)
Ruby treats fiscal_year_id as an identifier and tries to find either a local variable or a method named fiscal_year_id and checks if it is equal to 4. So even if you had assigned fiscal_year_id you're calling:
Tippani.where(true) # or false
Which isn't even close since you want evaluate WHERE tippanis.fiscal_year_id = 4 in the database.
Hashes in Ruby use hashrockets (=>) or colons (:):
# you can assign any type of key with hashrockets
{ :foo => :bar, 1 => "first", true => "yes", false => "no" }
# colons coerce the keys to symbols
{ a: 1, b: 2, c: 3, "this gets cast to a symbol": 4 }
Colons are generally preferred. When you call a method you can omit the braces as long as the hash is the last argument.
Tippani.where({ :fiscal_year_id => 4 }) # lots of noise
Tippani.where(fiscal_year_id: 4) # better
Also, is there some query method, where I could get all the tippani
instances, whose fiscal year is less than 2073 or some number.
Something like this:
Tippani.fiscal_year.where(year < 2074)
Again this won't work since < is an operator and the result of evaluating the expression is true or false.
ActiveRecord does not really have an elegant way of handling LT, GT, LTE and GTE conditions. So you either need to use a string:
Tippani.joins(:fiscal_year).where('fiscal_years.year < ?', 2074)
Or use Arel:
Tippani.joins(:fiscal_year).where(FiscalYear.arel_table[:year].lt(2074))

Answer 3

You need joins
Tippani.joins(:fiscal_year).where(fiscal_years: { id: 4 })
Second question also can be handled in similar way.
Tippani.joins(:fiscal_year).where("fiscal_years.year < ?", 2074)
Hope that helps!