Why is this Rails migration giving a 'no such table' error? - ruby-on-rails

Question

In a new Rails 6 project, I have a table named object_classes with a column named ClassList_id. From schema.rb:
create_table "object_classes", force: :cascade do |t|
t.string "name"
t.integer "ClassList_id", null: false
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.index ["ClassList_id"], name: "index_object_classes_on_ClassList_id"
end
I've realized that the column should be named class_list_id to conform with Rails expected naming convention. Therefore, I have generated a new migration:
class FixColumnName < ActiveRecord::Migration[6.0]
def change
rename_column :object_classes, :ClassList_id, :class_list_id
end
end
However, when I run this migration, I get the following error:
/bin/bash -c "env RBENV_VERSION=2.6.1 /home/asfarley/.rbenv/libexec/rbenv exec bundle exec ruby /home/asfarley/imgseq/bin/spring rails 'db:migrate'"
== 20200716060501 FixColumnName: migrating ====================================
-- rename_column(:object_classes, :ClassList_id, :class_list_id)
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:
SQLite3::SQLException: no such table: main.ClassLists
/home/asfarley/imgseq/db/migrate/20200716060501_fix_column_name.rb:3:in `change'
/home/asfarley/imgseq/bin/rails:9:in `<top (required)>'
/home/asfarley/imgseq/bin/spring:15:in `require'
/home/asfarley/imgseq/bin/spring:15:in `<main>'
Caused by:
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such table: main.ClassLists
/home/asfarley/imgseq/db/migrate/20200716060501_fix_column_name.rb:3:in `change'
/home/asfarley/imgseq/bin/rails:9:in `<top (required)>'
/home/asfarley/imgseq/bin/spring:15:in `require'
/home/asfarley/imgseq/bin/spring:15:in `<main>'
Caused by:
SQLite3::SQLException: no such table: main.ClassLists
/home/asfarley/imgseq/db/migrate/20200716060501_fix_column_name.rb:3:in `change'
/home/asfarley/imgseq/bin/rails:9:in `<top (required)>'
/home/asfarley/imgseq/bin/spring:15:in `require'
/home/asfarley/imgseq/bin/spring:15:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
Process finished with exit code 1
What am I doing wrong here? I'm looking for an explanation that addresses specifically what is wrong here, so that I can understand how to avoid this in the future.

Answer 1

Hard to know whether the fault is Rails or SQLite, but the issue seems to be that I had a foreign key defined for my object_classes table pointing to a table that didn't exist. With this migration, I was able to fix the foreign key constraint and rename the column:
class FixColumnName < ActiveRecord::Migration[6.0]
def change
remove_foreign_key :object_classes, :ClassLists
rename_column :object_classes, :ClassList_id, :class_list_id
add_foreign_key :object_classes, :class_lists
end
end

Answer 2

your syntax is ok so the error must be a reserved name error. may try and remove the column and creating the column again, watch out for capital letters on migrations for they can unnecessarily complicate your code. try this:
rails g migration RemoveClassListIdFromObjectClasses
that will created a migration kinda like this:
def drop
remove column :object_classes, :class_lis_id
end
and then run
rails g migration AddClassListIdToObjectClasses
the migration should look something like this:
def change
add_column :object_classes, :class_list_id
end
remember to add the data type and anything else you may need.
there you can check the migration it created and you can change it to maybe add the data type or maybe change the capitalization of the column and you will be set to go.
note: if it works i would appreciate if you accepted the answer, Thanks!