I have an old old app in Rails 2.3.14 I've inherited and I need to turn this SQL into a proper Rails up migration
ALTER TABLE gizmo_types ALTER gizmo_category_id SET NOT NULL
here is the original migration file
class NotNullGizmoCategoryId < ActiveRecord::Migration
def self.up
DB.execute("ALTER TABLE gizmo_types ALTER gizmo_category_id SET NOT NULL") <-- offending line
end
def self.down
end
end
This is using some sort of hack "DB.execute()" ...created by one of the former devs
...I need to turn this into a correct "Rails way" migration.
Maybe?...
change_column_null :gizmo_types, :gizmo_category_id, false"
...not sure.
What would the correct way be?
I have added new migration to change column type.
It worked well on my local.
But my team member have had the issue in migration since that column was not in migration.
It seems I had added that column manually in database.
To run migration without any issues for us(me and other team members), I want to add migration to create new column before the migration to change column type.
What is the way to do this?
Migration files have names like 20190616110000_create_foo.rb and are applied in the native alphabetical order.
Simply rename files changing the timestamps according to the order you need.
Another more proper way is in your migration (the change column type) you should add a condition to check if the column is there or not.
If it is already there (your local) then just change the column type. If it is not there (your colleagues local) then create a column with your desired type
if column_exists? :table_name, :column_name
change_column :table_name, :column_name, :type
else
add_column :table_name, :column_name, :type
end
I have a small problem that i am facing.
When i started the project i used scaffold and defined due_date field as Date
now i want to do some date calculations. and i need to change the due_date field to Datetime . Can sm1 help me with this
I know how to add new fields to table and delete but i am stuck at changing the attribute of already existing Model.
I have tried everything. Please let me know if there is any special code i can run in terminal to edit the attribute and create migration file.
P.s- Someone told me changing the schema file is bad. so i cant edit it directly.
first generate the migration
rails g migration change_date_format_in_my_table
then inside your migration file add
def up
change_column :my_table, :my_column, :datetime
end
def down
change_column :my_table, :my_column, :date
end
run your migration and its done. :)
How do I create a new field in an existing table using the Ruby command prompt?
I created the model (and migrated it) but I forgot to add a field - how would I go about this?
Generate a new migration to add a new column to table.
rails g migration add_column_name_to_table_name column_name:type
This will create a migration class like below:
#config/migration/20150304121554_add_column_name_to_table_name.rb
class AddColumnNameToTableName < ActiveRecord::Migration
def change
add_column :table_name, :column_name, :type
end
end
Here, column_name, table_name and type should be your desired name and type. Than run rake db:migrate command.
There are two ways to make changes in your situation:
Roll back the last migration
Add the new field in a new migration
Undoing the last migration should only be done if you have not yet pushed the migration to a public server. Here's how to do it:
Run rake db:rollback
Add the new field to the same migration file you originally used
Run rake db:migrate
Option 2:
To add the field in a new migration:
rails g migration AddFieldNameToTableName
For example, if your field is name and your table is users, you would run:
rails g migration AddNameToUsers
This will create a new migration file whose name starts with today's date and ends with add_name_to_users.rb. Open the file and add the field using the add_column command, like this:
class AddNameToUsers < ActiveRecord::Migration
def change
add_column :users, :name, :string
end
end
Save the file, then run rake db:migrate.
I encourage you to read the Rails migrations guide to learn more.
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?
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
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
BAD - running rake db:migrate and then rake db:rollback will fail
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
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.
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!
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)
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
rake db:migrate
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.
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
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.
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'"
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
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
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
Open you rails console
ActiveRecord::Base.connection.execute("drop table table_name")
ActiveRecord::Base.connection.drop_table :table_name
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
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"
Helpful documentation
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 table
rails 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 table
rails db:migrate
== 20211110174028 DropUsers: migrating ===============================
-- drop_table(:users, {:if_exist=>true})
-> 0.4607s
the best way you can do is
rails g migration Drop_table_Users
then do the following
rake db:migrate
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
Drop Table/Migration
run:-
$ rails generate migration DropTablename
exp:- $ rails generate migration DropProducts
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
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;
If you want to delete the table from the schema perform below operation --
rails db:rollback