Rails DB Migration - How To Drop a Table?
Ruby on-RailsRuby on-Rails-3MigrationRollbackDrop TableRuby on-Rails Problem Overview
I added a table that I thought I was going to need, but now no longer plan on using it. How should I remove that table?
I've already run migrations, so the table is in my database. I figure rails generate migration
should be able to handle this, but I haven't figured out how yet.
I've tried:
rails generate migration drop_tablename
but that just generated an empty migration.
What is the "official" way to drop a table in Rails?
Ruby on-Rails Solutions
Solution 1 - Ruby on-Rails
You won't always be able to simply generate the migration to already have the code you want. You can create an empty migration and then populate it with the code you need.
You can find information about how to accomplish different tasks in a migration here:
http://api.rubyonrails.org/classes/ActiveRecord/Migration.html
More specifically, you can see how to drop a table using the following approach:
drop_table :table_name
Solution 2 - Ruby on-Rails
First generate an empty migration with any name you'd like. It's important to do it this way since it creates the appropriate date.
rails generate migration DropProductsTable
This will generate a .rb file in /db/migrate/ like 20111015185025_drop_products_table.rb
Now edit that file to look like this:
class DropProductsTable < ActiveRecord::Migration
def up
drop_table :products
end
def down
raise ActiveRecord::IrreversibleMigration
end
end
The only thing I added was drop_table :products
and raise ActiveRecord::IrreversibleMigration
.
Then run rake db:migrate
and it'll drop the table for you.
Solution 3 - Ruby on-Rails
Write your migration manually. E.g. run rails g migration DropUsers
.
As for the code of the migration I'm just gonna quote Maxwell Holder's post [Rails Migration Checklist][1]
rake db:migrate
and then rake db:rollback
will fail
BAD - running class DropUsers < ActiveRecord::Migration
def change
drop_table :users
end
end
GOOD - reveals intent that migration should not be reversible
class DropUsers < ActiveRecord::Migration
def up
drop_table :users
end
def down
fail ActiveRecord::IrreversibleMigration
end
end
BETTER - is actually reversible
class DropUsers < ActiveRecord::Migration
def change
drop_table :users do |t|
t.string :email, null: false
t.timestamps null: false
end
end
end
[1]: http://maxwellholder.com/blog/rails-migration-checklist "Rails Migration Checklist"
Solution 4 - Ruby on-Rails
Warning: Do this at your own risk, as @z-atef and @nzifnab correctly point out, Rails will not be aware of these changes, your migration sequence fill fail and your schema will be different from your coworkers'. This is meant as a resource for locally tinkering with development only.
While the answers provided here work properly, I wanted something a bit more 'straightforward', I found it here: link First enter rails console:
$rails console
Then just type:
ActiveRecord::Migration.drop_table(:table_name)
And done, worked for me!
Solution 5 - Ruby on-Rails
You need to to create a new migration file using following command
rails generate migration drop_table_xyz
and write drop_table code in newly generated migration file (db/migration/xxxxxxx_drop_table_xyz) like
drop_table :tablename
Or if you wanted to drop table without migration, simply open rails console by
$ rails c
and execute following command
ActiveRecord::Base.connection.execute("drop table table_name")
or you can use more simplified command
ActiveRecord::Migration.drop_table(:table_name)
Solution 6 - Ruby on-Rails
- rails g migration drop_users
- edit the migration
class DropUsers < ActiveRecord::Migration
def change
drop_table :users do |t|
t.string :name
t.timestamps
end
end
end
3. rake db:migrate
Solution 7 - Ruby on-Rails
The simple and official way would be this:
rails g migration drop_tablename
Now go to your db/migrate and look for your file which contains the drop_tablename as the filename and edit it to this.
def change
drop_table :table_name
end
Then you need to run
rake db:migrate
on your console.
Solution 8 - Ruby on-Rails
I wasn't able to make it work with migration script so I went ahead with this solution. Enter rails console using the terminal:
rails c
Type
ActiveRecord::Migration.drop_table(:tablename)
It works well for me. This will remove the previous table. Don't forget to run
rails db:migrate
Solution 9 - Ruby on-Rails
I think, to be completely "official", you would need to create a new migration, and put drop_table in self.up. The self.down method should then contain all the code to recreate the table in full. Presumably that code could just be taken from schema.rb at the time you create the migration.
It seems a little odd, to put in code to create a table you know you aren't going to need anymore, but that would keep all the migration code complete and "official", right?
I just did this for a table I needed to drop, but honestly didn't test the "down" and not sure why I would.
Solution 10 - Ruby on-Rails
You can roll back a migration the way it is in the guide:
http://guides.rubyonrails.org/active_record_migrations.html#reverting-previous-migrations
Generate a migration:
rails generate migration revert_create_tablename
Write the migration:
require_relative '20121212123456_create_tablename'
class RevertCreateTablename < ActiveRecord::Migration[5.0]
def change
revert CreateTablename
end
end
This way you can also rollback and can use to revert any migration
Solution 11 - Ruby on-Rails
you can simply drop a table from rails console. first open the console
$ rails c
then paste this command in console
ActiveRecord::Migration.drop_table(:table_name)
replace table_name with the table you want to delete.
you can also drop table directly from the terminal. just enter in the root directory of your application and run this command
$ rails runner "Util::Table.clobber 'table_name'"
Solution 12 - Ruby on-Rails
Alternative to raising exception or attempting to recreate a now empty table - while still enabling migration rollback, redo etc -
def change
drop_table(:users, force: true) if ActiveRecord::Base.connection.tables.include?('users')
end
Solution 13 - Ruby on-Rails
Open you rails console
ActiveRecord::Base.connection.execute("drop table table_name")
Solution 14 - Ruby on-Rails
ActiveRecord::Base.connection.drop_table :table_name
Solution 15 - Ruby on-Rails
You can't simply run drop_table :table_name
, instead you can create an empty migration by running:
rails g migration DropInstalls
You can then add this into that empty migration:
class DropInstalls < ActiveRecord::Migration
def change
drop_table :installs
end
end
Then run rails db:migrate
in the command line which should remove the Installs table
The solution was found here
Solution 16 - Ruby on-Rails
if anybody is looking for how to do it in SQL.
type rails dbconsole
from terminal
enter password
In console do
USE db_name;
DROP TABLE table_name;
exit
Please dont forget to remove the migration file and table structure from schema
Solution 17 - Ruby on-Rails
I needed to delete our migration scripts along with the tables themselves ...
class Util::Table < ActiveRecord::Migration
def self.clobber(table_name)
# drop the table
if ActiveRecord::Base.connection.table_exists? table_name
puts "\n== " + table_name.upcase.cyan + " ! "
<< Time.now.strftime("%H:%M:%S").yellow
drop_table table_name
end
# locate any existing migrations for a table and delete them
base_folder = File.join(Rails.root.to_s, 'db', 'migrate')
Dir[File.join(base_folder, '**', '*.rb')].each do |file|
if file =~ /create_#{table_name}.rb/
puts "== deleting migration: " + file.cyan + " ! "
<< Time.now.strftime("%H:%M:%S").yellow
FileUtils.rm_rf(file)
break
end
end
end
def self.clobber_all
# delete every table in the db, along with every corresponding migration
ActiveRecord::Base.connection.tables.each {|t| clobber t}
end
end
from terminal window run:
$ rails runner "Util::Table.clobber 'your_table_name'"
or
$ rails runner "Util::Table.clobber_all"
Solution 18 - Ruby on-Rails
Run
rake db:migrate:down VERSION=<version>
Where <version>
is the version number of your migration file you want to revert.
Example:-
rake db:migrate:down VERSION=3846656238
Solution 19 - Ruby on-Rails
the best way you can do is
rails g migration Drop_table_Users
then do the following
rake db:migrate
Solution 20 - Ruby on-Rails
In migration you can drop table by:
drop_table(table_name, **options)
options:
:force
Set to :cascade to drop dependent objects as well. Defaults to false
:if_exists
Set to true to only drop the table if it exists. Defaults to false
Example:
-
Create migration for drop table, for example we are want to drop
User
tablerails g migration DropUsers Running via Spring preloader in process 13189 invoke active_record create db/migrate/20211110174028_drop_users.rb
-
Edit migration file, in our case it is
db/migrate/20211110174028_drop_users.rb
class DropUsers < ActiveRecord::Migration[6.1] def change drop_table :users, if_exist: true end end
-
Run migration for dropping
User
tablerails db:migrate == 20211110174028 DropUsers: migrating =============================== -- drop_table(:users, {:if_exist=>true}) -> 0.4607s
Solution 21 - Ruby on-Rails
Run this command:-
rails g migration drop_table_name
then:
rake db:migrate
or if you are using MySql database then:
- login with database
show databases;
show tables;
drop table_name;
Solution 22 - Ruby on-Rails
Drop Table/Migration
run:- $ rails generate migration DropTablename
exp:- $ rails generate migration DropProducts
Solution 23 - Ruby on-Rails
if you want to drop a specific table you can do
$ rails db:migrate:up VERSION=[Here you can insert timestamp of table]
otherwise if you want to drop all your database you can do
$rails db:drop
Solution 24 - Ruby on-Rails
If you want to delete the table from the schema perform below operation --
rails db:rollback