I need to add some columns to a table in my schema. Can someone tell me the best way to do this?
The following seems incomplete or wrong since the schema.rb file did not update to include the new column and all of the corresponding view files (edit,index,new,show) did not update to include the new column. Not to mention the bloat of all of those migration classes that get generated. Thanks
ruby script/generate migration RecordLabelToAlbums record_label:string
exists db/migrate
create db/migrate/20121130125859_record_label_to_albums.rb
Creates this:
class RecordLabelToAlbums < ActiveRecord::Migration
def self.up
end
def self.down
end
end
I then added this:
class RecordLabelToAlbums < ActiveRecord::Migration
def self.up
add_column :albums, :record_label, :text
end
def self.down
remove_column :albums, :record_label
end
end
The I ran:
rake db:migrate
Got This:
Mysql::Error: Table 'albums' already exists: CREATE TABLE albums (id int(11) DEFAULT NULL auto_increment PRIMARY KEY, created_at datetime, updated_at datetime)
The code you added is correct.
The error suggests that for some reason your system appears to think it has not yet run the original migration that created the albums table. The state of migrations (in Rails 2) is specified in a table in the database called schema_migrations -- if this gets confused then it will try to re-run migrations. I am not sure what might cause it to get confused, but I do recall this happened a couple times back in 2008 when I was using Rails 2.x.
The table is simple -- you can see what's in it from a SQL prompt -- just the names of migrations it thinks it has run, I think.
If you don't mind losing some data, you can try rake db:rollback or even rake db:reset to get back to the beginning. rake db:rollback STEP=2 will rollback the last 2 migrations.
If you need the data, correct the contents of the table by adding one or more new records referencing the migrations in app/db/migrations that may have been missed. The order is important, I think (the format changed a little in Rails 3, I don't recall how).
Any time you want to add or change the database schema, use rails to generate a migration, and then run rake db:migrate once it's ready to go.
And just asking: is there any way you can move to Rails 3. It's been out for years now, and Rails 4 is coming soon. You'll find yourself in a backwater of incompatibilities, deprecations, security and performance issues and so on if you don't take the hit and upgrade.
I've got a problem trying to rollback one of my migration. It seems as if Rails is generating a temporary table for the migration, with temporary indices. My actual index on this table is less than 64 characters, but whenever Rails tries to create a temporary index for it, it turns into a name longer than 64 characters, and throws an error.
Here's my simple migration:
class AddColumnNameToPrices < ActiveRecord::Migration
def self.up
add_column :prices, :column_name, :decimal
end
def self.down
remove_column :prices, :column_name
end
end
Here's the error I'm getting:
== AddColumnNameToPrices: reverting ============================================
-- remove_column(:prices, :column_name)
rake aborted!
An error has occurred, this and all later migrations canceled:
Index name 'temp_index_altered_prices_on_column_and_other_column_and_third_column' on table 'altered_prices' is too long; the limit is 64 characters
I've changed the column names, but the example is still there. I can just make my change in a second migration, but that still means I can't rollback migrations on this table. I can rename the index in a new migration, but that still locks me out of this single migration.
Does anyone have ideas on how to get around this problem?
It looks like your database schema actually has index called prices_on_column_and_other_column_and_third_column. You have probably defined the index in your previous play with migrations. But than just removed index definition from migrations.
If it is true you have 2 options:
The simplier one (works if you code is not in production). You can
recreate database from scratch using migrations (not from
db/schema.rb) by calling rake db:drop db:create db:migrate. Make sure that you do not create this index with long name in other migration files. If you do, add :name => 'short_index_name' options to add_index call to make rails generate shorter name for the index.
If you experience this problem on a production database it is a bit more complicated. You might need to manually drop the index from the database console.
Had this problem today and fixed it by changing the migration to include the dropping and adding of the index causing the long name issue. This way the alteration is not tracked while I am altering the column type (that is where the really long name is caused)
I added the following:
class FixBadColumnTypeInNotifications < ActiveRecord::Migration
def change
# replace string ID with integer so it is Postgres friendly
remove_index :notifications, ["notifiable_id","notifiable_type"]
change_column :notifications, :notifiable_id, :integer
# shortened index name
add_index "notifications", ["notifiable_id","notifiable_type"], :name => "notifs_on_poly_id_and_type"
end
end
I have inherited a Ruby on Rails project where the programmer didn't use rake to create the db schema, so it seems very out of synch, is there a way to rectify this?
First create a schema.rb file
rake db:schema:dump
Then make a migration ot of it.
class CreateMigration < ActiveRecord::Migration
def self.up
# insert schema.rb here
end
def self.down
end
end
You might also need to create the schema_migrations table, and manually add the timestamp for this migration to it.
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
Is it possible to rename a column using a command like:
script/generate migration AddColumnToTable column:type
? Thanks.
Rails does have a migration command on the ActiveRecord ConnectionAdapter called rename_column. You can generate a migration and then write the code yourself. example (MySQL):
script/generate migration rename_my_column_by_hand
Then edit the file it creates:
class RenameMyColumnByHand < ActiveRecord::Migration
def self.up
rename_column :my_table, :old_name, :new_name
end
def self.down
rename_column :my_table, :new_name, :old_name
end
end
It executes SQL like:
ALTER TABLE my_table CHANGE old_name new_name BIGINT;
Note This only renames the column, it won't rename any references you have to it on other tables.
Great question. The answer is, unfortunately, no. See Rails 2.3.5 source code:
lib/rails_generator/generators/components/migration/migration_generator.rb
The only keywords that are recognized by the migration generator are add, remove, and to/from.
I use a bit of trickery here. Say I want to change column foo to bar.
Create a migration with the following steps
Add a temporary column temp_foo
Update all records, saving foo's value in temp_foo
Add a bar column
Update all records, saving temp_foo's value in bar
Drop column foo
Drop column temp_foo
This is ex-tre-me-ly brittle. If one step fails, you might loose data..