Active Record - store vs store_accessor

Imagine this: you get a task to add a Questionnaire feature to the app. It needs to support a variety of questions and must be delivered fast. A JSON column seems perfect for flexible data storage, but how do you integrate it with Rails?

Active Record store

After a quick research, you discover Active Record store method. It adds reader and writer accessors for a defined collection of keys. It also provides dirty tracking and prefix/suffix if needed. Let's try it:

# db/migrate/20250109092657_create_questionnaires.rb

class CreateQuestionnaires < ActiveRecord::Migration[8.0]
  def change
    create_table :questionnaires do |t|
      t.jsonb :questions
      t.string :title

      t.timestamps
    end
  end
end

The model looks like:

# app/models/questionnaire.rb

class Questionnaire < ApplicationRecord
  QUESTION_LIST = %w[question1 question2]

  store :questions, *QUESTION_LIST
end

And you can test it:

require "test_helper"

class QuestionnaireTest < ActiveSupport::TestCase
  test "stores questions in jsonb column" do
    questionnaire = Questionnaire.new
    questionnaire.question1 = "How are you?"
    questionnaire.question2 = "How old are you?"

    questionnaire.save!

    questionnaire.reload
    assert_equal questionnaire.question1, "How are you?"
    assert_equal questionnaire.question2, "How old are you?"
  end
end

Fast and easy, job done. 🎉

But a few weeks after the release, the data team guy comes to you and says: "We need to analyze the questionnaire table, but it contains invalid JSON. Please, fix it."
Sure. 🕵️

You go to the database and see the content of the column. It looks like YAML:

"---\\nquestion1: How are you?\\nquestion2: How old are you?\\n"

Oh! By default, Rails uses the YAML format for data serialization. Let's explicitly add the coder option to the store method (as per documentation). Updating the model should help:

# app/models/questionnaire.rb

class Questionnaire < ApplicationRecord
  QUESTION_LIST = %w[question1 question2]

  store :questions, *QUESTION_LIST, coder: JSON
end

How does the content of the database look now?

"{\\"question1\\":\\"How are you?\\",\\"question2\\":\\"How old are you?\\"}"

It's not a JSON object, it's a JSON string. 🤔
The test is green, which means Rails can serialize it properly, but the content stored in the database is still not a high-quality JSON. We can tell because searching with JSON operators still does not work.

Store_accessor

Confused at this point, let's go back to documentation. There is a NOTE:

NOTE: If you are using structured database data types (e.g. PostgreSQL hstore/json, MySQL 5.7+ json, or SQLite 3.38+ json) there is no need for the serialization provided by .store. Use .store_accessor instead to generate the accessor methods. Be aware that these columns use a string keyed hash and do not allow access using a symbol.

Right! 🤦
You do use structured database type. This means you should not use the store method. Just stick to store_accessor instead:

# app/models/questionnaire.rb

class Questionnaire < ApplicationRecord
  QUESTION_LIST = %w[question1 question2]

  store_accessor :questions, *QUESTION_LIST
end

And test if searching with JSON operators works:

require "test_helper"

class QuestionnaireTest < ActiveSupport::TestCase
  test "stores questions in jsonb column" do
    questionnaire = Questionnaire.new
    questionnaire.question1 = "How are you?"

    questionnaire.save!

    assert_equal questionnaire.reload.question1, "How are you?"
    assert_equal questionnaire.id,
      Questionnaire.where("questions ->> 'question1' = 'How are you?'").first.id
  end
end

Eventually, beautiful JSON resides in the database column:

{
  "question1": "How are you?",
  "question2": "How old are you?"
}

Conclusion

When working with structured data types like JSON or JSONB columns, use the store_accessor method. On the other hand, Active Record store method works fine for older use cases: simple key-value store in plain text columns. If in doubt, read the documentation carefully.

P. S. There is a simple Rails app repo with code examples.