How To Add Array To Existing Table Ruby On Rails​

In today’s dynamic web applications built with Ruby on Rails, handling flexible and scalable data structures is a fundamental requirement. 

Many apps need to store lists of values, like tags, preferences, or categories, within a single table column. With PostgreSQL support, Rails developers can easily add array columns to existing tables for efficient storage and querying. 

If you’re just getting started with Ruby on Rails and want an easy way to store lists like tags or preferences, this simple guide shows you how to add an array column to any table using PostgreSQL. 

With quick migration steps, basic code examples, and practical usage tips, you’ll learn how to manage multi-value fields in your Rails app, even if you’re new to database arrays.

Why Use Array Columns?

Array columns let you store multiple values of the same data type in a single database field. This is especially useful for:

• Managing tags in blogging or e-commerce platforms.
  
• Storing user-selected preferences or permissions.
  
• Capturing multi-select form results without additional tables.

However, array columns are only supported natively in PostgreSQL. For other databases, consider serialization or joins.

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Adding an Array Column to an Existing Table in Rails

This is the step-by-step process that you can use to add an array to an existing table in Ruby on Rails​

Step 1: Understanding Database Support

Rails supports array columns exclusively through PostgreSQL. Migrating and manipulating arrays is straightforward but requires certain database setup.

Key Requirements:

• PostgreSQL
  
• Rails 4.2+ (for native array migration support)

Step 2: Writing the Migration

Suppose you have a products table and want to add an array column tags to store multiple tags for each product.

class AddTagsToProducts < ActiveRecord::Migration[6.1]
  def change
    add_column :products, :tags, :string, array: true, default: []
  end
end

Explanation:

• :tags is the new column name.
  
• :string specifies the data type inside the array.
  
• array: true tells Rails to generate a PostgreSQL array column.
  

• default: [] ensures existing rows have an empty array by default.

Run the migration in bash:

rails db:migrate

This updates your schema and creates the column in PostgreSQL.

Output:

Upon successfully running the migration, your database schema (db/schema.rb) will now include:

create_table "products", force: :cascade do |t|
  t.string "tags", default: [], array: true
end

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Step 3: Model and Validation Changes

You don’t need to change your model for basic usage, as Rails will recognize the array column automatically. If desired, to ensure the integrity of the data (i.e., that the column is always an array of strings), use a custom validation in your model:

class Product < ApplicationRecord
validate :tags_must_be_array_of_strings

def tags_must_be_array_of_strings
  unless tags.is_a?(Array) && tags.all? { |t| t.is_a?(String) }
    errors.add(:tags, "must be an array of strings")
  end
end

Step 4: Using the Array Column in Code

Create or update records with array data:

product = Product.create(name: 'Ruby T-Shirt', tags: ['apparel', 'ruby', 'rails'])
product.tags # => ['apparel', 'ruby', 'rails']

Query by array values:

Find products with a specific tag using PostgreSQL’s array query syntax:

Product.where("'rails' = ANY(tags)")

Find products with any of several tags:

Product.where("tags && ARRAY[?]::varchar[]", ['rails', 'apparel'])

Update tags:

product.tags << 'new'
product.save

Remove a tag:

product.tags.delete('rails')
product.save

Step 5: Displaying Array Data

To render tags in a view:

(text)

<ul>
  <% @product.tags.each do |tag| %>
    <li><%= tag %></li>
  <% end %>
</ul>

Output example:

• “apparel”
  
• “ruby”
  
• “rails”
  
• “new”

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Step 6: Useful Tips and Considerations

• Always set a default value (empty array) for array columns to prevent nil errors.
  
• Index array columns only when needed. Use GIN indexes for performance:
  

ruby

add_index :products, :tags, using: 'gin'

• Keep in mind that complex querying on arrays is PostgreSQL-specific.
  
• For large-scale tagging, consider extracting tags into their own table for normalization.

Step 7: Advanced Examples

Migration for Integer Array:

add_column :orders, :item_ids, :integer, array: true, default: []

Example usage:

order = Order.create(item_ids: [1, 2, 3])
order.item_ids # => [1, 2, 3]

Query for items in array:

Order.where("1 = ANY(item_ids)")

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Conclusion

Adding array columns to an existing Rails table is a powerful technique for handling multi-value attributes, such as tags or preferences, in a clean, scalable manner. 

By leveraging PostgreSQL’s native array support and Rails migrations, developers can streamline the storage and retrieval of lists directly within their models. 

This approach enhances both code simplicity and performance, providing flexibility for evolving business needs while maintaining robust, maintainable database structures suitable for real-world production environments.

Ramesh Vayavuru

Verified Expert 15+ Years of experience

Ramesh Vayavuru is the Founder & CEO of Soft Suave Technologies, a leading offshore software development company that delivers innovative IT solutions to businesses across the globe. With over 15 years of experience in the technology industry, Ramesh has been instrumental in building a team of highly skilled professionals dedicated to providing reliable, scalable, and cost-effective software services.

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