how to change the index of the table that was already created using rails migration?

Question

I already have this migration file that was created and the migration was run.

class CreateStudentContexts < ActiveRecord::Migration
  def change
    create_table :student_contexts do |t|
      t.string :student_id, index: true, null: false, limit: 40
      t.text :data
      t.timestamps null: false

      t.index [:student_id, :updated_at], unique: true, name: 'student_context_index'
    end
  end
end

Now i want to create a new migration file that will update the index, and the index fields should be student_id and created_at.

Answer 1

This question is kinda old, but in case anyone comes across it:

Justin Wood's answer should work, but with one change: replace the column name in the remove_index method with the name of the index:

remove_index :student_contexts, name: 'student_context_index'

When the index was created, it was given a specific (non-standard) name with the name argument, so you also need to use the name argument in the remove_index statement. Otherwise, Rails expects the index to have a standard name (in this case "index_student_contexts_on_updated_at").

Answer 2

You can create another migration and change the table. Something like

class MyMigration < ActiveRecord::Migration
  def change
    remove_index :student_contexts, :updated_at
    add_index :student_contexts, :created_at
  end
end

would do.