bulk_create.rb

# When creating a lot of records from an array of hashes
new_users = [
  {name: "Teemo", email: "[email protected]"},
  {name: "Heim", email: "[email protected]"},
  {name: "Annie", email: "[email protected]" },
  ...
  {name: "Volli", email: "[email protected]" },
]

# Do not create each one individually as it results in one query, per record.
new_users.each do |user_hash|
  User.create(user_hash)
end
# INSERT INTO users (name, email) VALUES ('Teemo', '[email protected]');
# INSERT INTO users (name, email) VALUES ('Heim', '[email protected]');
# INSERT INTO users (name, email) VALUES ('Annie', '[email protected]');
# ...
# INSERT INTO users (name, email) VALUES ('Volli', '[email protected]');

# Instead, pass the array into ActiveRecord::Base#create, which will create
# all the records in one query if the database supports this feature.
User.create(new_users)
# INSERT INTO users (name, email) 
# VALUES 
#   ('Teemo', '[email protected]'),
#   ('Heim', '[email protected]'),
#   ('Annie', '[email protected]'),
#   ....
#   ('Volli', '[email protected]');