Rails Rake Task - How to Delete Records - ruby-on-rails

Question

I am trying to use a daily RAKE task to synchronize a users table in my app with a CSV file.
My import.rake task successfully imports records that aren't found in the table (find_or_create_by_username), but I don't know how to delete records from the table that are no longer found in the CSV file. What should I use instead of "find_or_create_by_username" to achieve this? Thanks in advance.
#lib/tasks/import.rake
desc "Import employees from csv file"
task :import => [:environment] do
file = "db/testusers.csv"
usernames = [] # make an array to collect names
CSV.foreach(file, headers: true) do |row|
Employee.find_or_create_by_username({
# Add this line:
username = row[0]
:username => username,
:last_name => row[1],
:first_name => row[2],
:employee_number => row[3],
:phone => row[4],
:mail_station => row[5]
}
)
# Collect the usernames
usernames << username
end
# Delete the employees (make sure you fire them first)
Employee.where.not( username: usernames ).destroy_all
end

Answer 1

You can achieve this by doing like the following:
#lib/tasks/import.rake
require 'csv'
desc "Import employees from csv file"
task :import => [:environment] do
file = "db/users.csv"
employee_ids_to_keep = []
CSV.foreach(file, headers: true) do |row|
attrs = {
:username => row[0], :last_name => row[1], :first_name => row[2],
:employee_number => row[3], :phone => row[4],:mail_station => row[5]
}
# retrieves the Employee with username
employee = Employee.where(username: attrs[:username]).first
if employee.present? # updates the user's attributes if exists
employee.update_attributes(attrs)
else # creates the Employee if does not exist in the DB
employee = Employee.create!(attrs)
end
      # keeps the ID of the employee to not destroy it
employee_ids_to_keep << employee.id
end
Employee.where('employees.id NOT IN (?)', employee_ids_to_keep).destroy_all
end

Answer 2

Get a list of all ID's in the database and store them in a set. Then as you do your importing, remove valid employees from the set. Once you're done, any ID's left in the set need to be removed from the database.
Something like this...
existing_ids = Employee.pluck(:id).to_set
CSV.foreach(file, headers: true) do |row|
employee = Employee.find_or_create_by.....
existing_ids.delete(employee.id)
end
Employee.destroy(*existing_ids.to_a) unless existing_ids.empty?

Answer 3

usernames = [] # make an array to collect names
CSV.foreach(file, headers: true) do |row|
username = row[0]
Employee.find_or_create_by_username({
:username => username,
:last_name => row[1],
:first_name => row[2],
:employee_number => row[3],
:phone => row[4],
:mail_station => row[5]
}
)
# Collect the usernames
usernames << username
end
# Delete the employees (make sure you fire them first)
Employee.where.not( username: usernames ).destroy_all
where.not will work with rails 4 of course.