How to check if a column already exists in rails?

less than 1 minute read

Developers often need to check if a column already exists in the database schema. Rails provides built-in method to accomplish this effectively.

Syntax

column_exists?(table_name, column_name, type = nil, **options)

Example

Here is an example of how to use column_exists? method:

class AddEmailToUsers < ActiveRecord::Migration[7.1]
  def change
    unless column_exists?(:users, :email)
      add_column(:users, :email, :string)
    end
  end
end

Following are some more examples of how to use column_exists? method:

# Checks if a column exists
column_exists?(:users, :email)

# Checks if a column with string type exists
column_exists?(:users, :email, :string)

# Checks if a column exists with a specific definition
column_exists?(:products, :name, :string, limit: 100)
column_exists?(:products, :name, :string, null: false)
column_exists?(:products, :status, :string, default: "pending")
column_exists?(:products, :price, :decimal, precision: 8, scale: 2)

NOTE: This can also be re-written using the if_not_exists option in the add_column method.

class AddEmailToUsers < ActiveRecord::Migration[7.1]
  def change
    add_column(:users, :email, :string, if_not_exists: true)
  end
end

References

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