How do I set the isolation level of all my rails transactions

Question

I'm using RoR version 4.2.3, and I understand I can set the isolation level of my transactions. However, where do I define setting the isolation level of all transactions? so I only have to define it once and then not worry about it?

I'm using postgreSQL as my database

Answer 1

There does not seem to be a global isolation option, thus you are left with four options:

1. Monkeypatch existing transaction implementation, so that it picks your desired isolation level. (Monkeypatching is not desirable)

2. Use correct isolation level throughout your application.

   SomeModel.transaction(isolation: :read_committed)

3. Extend ActiveRecord and create your own custom transaction method.

4. As commented - you may be able to edit the default isolation level in DB configuration. For postgres it's this one

Example code:

#lib/activerecord_extension.rb
module ActiveRecordExtension
  extend ActiveSupport::Concern

  module ClassMethods
    def custom_transaction
      transaction(isolation: :read_committed) do
        yield
      end
    end
  end
end

ActiveRecord::Base.send(:include, ActiveRecordExtension)

Then in your initializers:

#config/initializers/activerecord_extension.rb
require "active_record_extension"

Afterwards you can use:

MyModel.custom_transaction do
  <...>
end

And in the future, this will allow you to change the isolation level in one place.

Answer 2

Rails doesn't support setting a global isolation level, but Postgres lets you set one for a session. You can hook into Rails' connection establishment to run a command every time a connection is made, thought the techniques for this all rely on monkeypatching and may be questionable.

• Run Raw SQL in Rails after connecting to Database
• Can I hook into ActiveRecord connection establishment?

Then configure your isolation level with:

SET SESSION CHARACTERISTICS AS TRANSACTION transaction_mode

Though this is interesting, I'd go with something more like Magnuss's answer for maintainability and sanity.