One case of solving a migration error in Rails

This time, I failed in the migration, consulted with the mentor, and wrote a memo until the solution. I was making something like an app that counts likes with online school materials. I put in the code to count the likes and ran the migration, but apparently it didn't work.

Migration error occurred

When you run rails db: migrate,

An error has occurred, this and all later migrations canceled:PG::UndefinedColumn: ERROR: column "likes_count" of relation "posts" does not existLINE 1: UPDATE "posts" SET "likes_count" = $1 WHERE "posts"."id" = $... I got the error.

It was Google Translate, but it seemed to be angry that "likes_count does not exist in the post column!".

Check rails db: migrate: status

I received an instruction from a mentor saying "Please check rails db: migrate: status. " When I check it,

database: like_app_development

 Status   Migration ID    Migration Name
   up     20201221071016  Devise create users
   up     20201221072319  Create posts
   up     20201221223916  Create likes
   up     20201222001044  Add likes count to posts
  down    20201222001313  Reset all post cache counters

Apparently, the likes count wasn't added well in the 20201222001044 part.

rails db: rollback

File in question,


class AddLikesCountToPosts < ActiveRecord::Migration[6.1]
  def change
    add_column :posts, :likes_count, :integer, default: 0

Comment this out and roll back using the rails db: rollback command. Then comment out and run rails db: migrate again. The migration was done correctly, and we were able to confirm the operation properly! !! : clap :: clap ::


I think the failure this time was probably because I had migrated before putting in likes_count. When migrating, I would like to confirm the files properly before executing. Even so, I was able to solve it immediately with the quick response of the mentor. Thank you, thank you!

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