niaomingjian niaomingjian - 1 year ago 174
Ruby Question

How to undo the action of rails db:migrate in Rails

When migrating the database, I made a spelling mistake.

I want to generate a scaffold by running:

rails generate scaffold Micropost context:text user_id:integer
rails db:migrate

Although I made a mistake by leaving out the colon when I ran:

rails generate scaffold Micropost context:text user_id integer
rails db:migrate

I want to undo this migration, how to do it?
(I'm using Rails

When I run
rails db:migrate
, I get an error of:

SQLite3::SQLException: table "microposts" already exists:

When I run
rails db:migrate:status
, I get the following output:

Status Migration ID Migration Name
up 20161024021157 Create users
up 20161024025545 ********** NO FILE **********
down 20161024025805 Create microposts

I tried to use
rails db:migrate:down VERSION=20161024025805
. There wasn't any message showing in the command line. Then I ran
rails db:migrate
. The error is the same.

Answer Source

rails db:rollback will simply rollback one migration which I believe is what you are looking for

For a more specific rollback, you can run rails db:migrate:down VERSION=numberofversion

Replace the numberofversion with the version number of the migration file generated, for example:

rails db:migrate:down VERSION=1843652238


Since you are getting the error that the Microposts table already exists, you must follow these steps to remove the table:

  1. Run rails generate migration DropMicroposts
  2. Go to the /db/migrate folder and find the latest migration file you just created
  3. In that file paste this:

    class DropMicroposts < ActiveRecord::Migration 
      def up 
        drop_table :microposts 
  4. run rails db:migrate

  5. After this, run rails generate scaffold Micropost context:text user_id:integer
  6. Then run rails db:migrate
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