Avoid N+1 Queries in Rails

How to eager load the data

i have three models called City, User, Bank

so i need to eager load the data to avoid N+1 Queries

here in my method of city.rb

def update_data(activity = false) # Used in delayed Job# Filtering the Users

#here i need to filter the users based on the activity#if the activity is true then i need to fetch all the users of the cityelse i need to fetch the users who belongs to the city where the bank of the user has enabled_banking flag false and those user who dont have any bankso i have written a query like  filtered_users = activity ? users : users.left_joins(:banks).where("(banks.enabled_banking = ?) OR (banks.id IS NULL)", false)   

#then

filtered_users.find_in_batches do |city_users|  city_users.each do |user|    user.format_and_process  endend

end

but i need to avoid n+1 queries in both cases, fetching all the users and also when i append the left join to fetch the records.

How to achieve this

previously i updated like

users.includes(:city, :bank)

then

 filtered_users = activity ? users : users.left_joins(:banks).where("(banks.enabled_banking = ?) OR (banks.id IS NULL)", false).references(:banks)but this will not the optimzed way to fetch the records.How we can achieve this expected behaviour?