How to rename database columns in Rails

18 Feb 2020

Often when I begin a project, I find myself rolling back migrations, dropping the database, renaming tables and columns whilst I figure out the shape of the model. If I need to rename a column, I’ll just update or delete the corresponding migration.

However, it is possible to change a column’s name in a migration.

Say, I have a table tasks and I want to change the name of the title column to name. First I ask Rails to generate the migration:

rails generate migration rename_title_to_name_in_tasks

The generated migration looks like this:

class RenameTitleToNameInTasks < ActiveRecord::Migration[6.0]
  def change
  end
end

I then remove change and add the up and down migration like so:

class RenameTitleToNameInTasks < ActiveRecord::Migration[6.0]
  def up
    rename_column :tasks, :title, :name
  end

  def down
    rename_column :tasks, :name, :title
  end
end

rename_column takes three arguments. The first is the table name. The second is the existing column name. The third is the new name.

Above, I have defined the up and down migration. That is, the up migration does the renaming bit when we migrate the database. The down migration runs when we roll back the migration – in this instance, it reverts the column’s name back to the original.

Before I run the migration, I give the schema a quick check.

  create_table "tasks", id: :uuid, default: -> { "gen_random_uuid()" }, force: :cascade do |t|
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.string "title", null: false
    t.text "notes", default: ""
    t.uuid "task_list_id"
    t.uuid "fulfiller_id"
    t.datetime "completed_at", precision: 6
    t.index ["fulfiller_id"], name: "index_tasks_on_fulfiller_id"
    t.index ["task_list_id"], name: "index_tasks_on_task_list_id"
  end

Then, after running rails db:migrate, I check it again to see if the migration has worked:

  create_table "tasks", id: :uuid, default: -> { "gen_random_uuid()" }, force: :cascade do |t|
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.string "name", null: false
    t.text "notes", default: ""
    t.uuid "task_list_id"
    t.uuid "fulfiller_id"
    t.datetime "completed_at", precision: 6
    t.index ["fulfiller_id"], name: "index_tasks_on_fulfiller_id"
    t.index ["task_list_id"], name: "index_tasks_on_task_list_id"
  end

All done!

Of course, five minutes later, I might decide that the new name probably isn’t the best and I can run rails db:rollback. On doing so, I can see that the column name has reverted to title.