Rails 7 adds the partial_inserts config to config.active_record that is used to control partial writes when creating a new record.

config.active_record.partial_inserts is a boolean value and controls whether or not partial writes are used when creating new records (i.e. whether inserts only set attributes that are different from the default).

Configuring config.active_record.partial_inserts

In a newly created Rails 7.0 application, config.load_defaults 7.0 is set by default in application.rb. The default value of partial_inserts for config.load_defaults 7.0 is false and for config.load_defaults < 7.0 it is true. To opt-in:

# config/environments/development.rb

config.active_record.partial_inserts = true

Also, partial_writes is deprecated in favor of partial_inserts and partial_updates. We will discuss partial_inserts in this blog.

2.7.0 :001 >  ActiveRecord::Base.partial_writes
# DEPRECATION WARNING: ActiveRecord::Base.partial_writes is deprecated and will be removed in Rails 7.1. Use `partial_updates` and `partial_inserts` instead. (called from irb_binding at (irb):3)
# => false
2.7.0 :002 >  ActiveRecord::Base.partial_writes = false
# DEPRECATION WARNING: `ActiveRecord::Base.partial_writes=` is deprecated and will be removed in Rails 7.1. Use `partial_updates=` and `partial_inserts=` instead. (called from irb_binding at (irb):4)

Let's take an example of the following Article model structure:

# == Schema Information
#
# Table name: articles
#
#  id                     :integer(4)
#  title                  :string
#  body                   :text          default('New Article')
#  created_at             :datetime
#  updated_at             :datetime

class Article < ApplicationRecord
end

  1. When config.active_record.partial_inserts = true

    • When inserting new records, only the fields that have been changed from the defaults will be included in the INSERT statement.

    • In the below example, the unchanged field body is not included in the INSERT query.

    Loading development environment (Rails 7.0.0.alpha)

2.7.0 :001 >  Rails.configuration.active_record.partial_inserts
  => true
2.7.0 :002 > Article.new(title: 'Rails 7').save
     (1.1ms)  SELECT sqlite_version(*)
TRANSACTION (0.1ms)  begin transaction
Article Create (1.7ms)  INSERT INTO "articles" ("title", "created_at", "updated_at") VALUES (?, ?, ?)  [["title", "Rails 7"], ["created_at", "2021-09-06 04:13:01.580819"], ["updated_at", "2021-09-06 04:13:01.580819"]]
TRANSACTION (1.9ms)  commit transaction
  => true

  2. When config.active_record.partial_inserts = false

    • This default means that all columns will be referenced in INSERT queries regardless of whether they have a default or not. The other fields will be populated by the database.

    • In the below example, the unchanged field body is included in the INSERT query.

    Loading development environment (Rails 7.0.0.alpha)

2.7.0 :001 >  Rails.configuration.active_record.partial_inserts
  => false
2.7.0 :002 > Article.new(title: 'Rails 7').save

TRANSACTION (0.1ms)  begin transaction
Article Create (0.6ms)  INSERT INTO "articles" ("title", "body", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["title", "Rails 7"], ["body", "New Article"], ["created_at", "2021-09-29 07:46:46.236842"], ["updated_at", "2021-09-29 07:46:46.236842"]]
TRANSACTION (5.6ms)  commit transaction
  => true

Note:

  • Additionally, partial_inserts prevents removing the default value of a column safely. If a migration removes the default value of a column, this option would cause old processes to no longer to be able to create new records.
  • If you need to remove a column, you should first use ignored_columns to stop using it. ActiveRecord::Base.ignored_columns is introduced in Rails 5 to make some columns invisible from ActiveRecord. Ignored columns won’t have attribute accessors defined, and won’t be referenced in SQL queries.

In your rails application, based on your requirements you can set the partial_inserts config value. Hope this article has helped you to understand the use of partial_inserts config of active-record.

Thank you for reading. ❤️

References