I'm an idiot...screwed up a migration in Rails:
thinking migrations would work like model generators (using references:modelname) I did the following:
$ rails g migration add_event_to_photos references:event
which created the migration
class AddEventToPhotos < ActiveRecord::Migration
def change
add_column :photos, :references, :event
end
end
And now my development database (SQLite3) has a references column of type event in the photos table.
And my schema.rb has a line in the middle saying:
# Could not dump table "photos" because of following StandardError
# Unknown type 'event' for column 'references'
rake db:rollback is powerless against this:
$ rake db:rollback
== AddEventToPhotos: reverting ===============================================
-- remove_column("photos", :references)
rake aborted!
An error has occurred, this and all later migrations canceled:
undefined method `to_sym' for nil:NilClass
So, how to roll back and maintain my development data in the database? I'd even be happy trashing the photos table if that's my only choice..but don't want to have to rebuild the whole thing. What to do?
btw- for anyone reading this about to make same stupid mistake...don't! Use the correct migration generator:
$ rails g migration add_event_to_photos event_id:integer
The easiest way I found to do this was to recreate the table in the schema.rb file in /db/. Afterwards I ran a rake db:reset (if it says you have pending migrations, just delete them and try again).
This took care of the problem.
Go into the database by ./script/rails dbconsole. Then type these commands:
.output dump.sql
.dump
In the file dump.sql you will have the SQL commands used to recreate and populate your database. Just edit it with your favourite editor (like vim ;-) removing or fixing the column type. You may also remove the invalid migration identifier from the schema_migrations table. Drop your database (I suggest just rename the db/development.sqlite file), create new database and read the dump file into it (using command .read dump.sql).
Now you just need to fix and run your migrations.
add an empty down method and run rake db:rollback
edit ahh that's the new migration syntax, you can replace the body with simply:
def self.down; end
which is the old syntax, or perhaps delete the body altogether (haven't tried this) and then run rake db:rollback
Just an idea, I know it's not SQLite specific you can revert to an older version schema perhaps, load it up. And try again from there? You can revert (checkout) specific files in GIT. And then do def self.down; end, as was suggested by another poster.
The problem arises because while SQLite will create the schema with whatever type you give it (in this case event it can't dump that type back to ActiveRecord.
You need to edit the sqlite_master file and change create table string (sql) to be the right thing.
You probably want to back up your table first since messing up that string will wreck your table if you do it wrong.
Here is a related rails issue
Related
So I've been going through a lot of rails tutorial, and I get that the default for adding a new column to a database is , for example,
rails generate migration add_reset_to_users reset_digest:string reset_sent_at:datetime
The above will add a reset_digest in the form of a string and reset_sent_at in the form of a date to the migration add_reset_to_users
My questions is what if I am clumsy one night at 4 AM and only call the following
rails generate migration add_reset_to_users reset_digest:string
I completely forgot about reset_sent_at but want to implement it the next morning. I made the mistake of adding the link directly to the db file, which was a huge mistake.
In this case what should I do? Do I simply call a new migration such as
rails generate migration add_reset_sent_to_users reset_sent_at:datetime
or is there an even better way?
first, if you have not run your migration, you can directly open the migration file, and add your column to the file, as
def change
add columns :table_name :column_name :column_type
end
In your case, you will modify the file as,
def change
add columns :users :reset_digest :string
add columns :users :reset_sent_at :datetime
end
and then run
rake db:migrate
if you have already ran your migration, and you have not run any other migration after that, you can undo it, by
rake db:rollback STEP=1
and then edit the migration file, and run your migration
Rule of thumb for migrations in Rails is that you always create a new migration file unless you have not already shared your code with others, i.e. pushed to remote repository, otherwise you can just change the old migration after running $ rake db:rollback and everything will be fine, and nobody will know about it, and won't affect other developers work(since it's still on your local repository).
So, I'd encourage you to create a new migration if you have already committed and pushed the code onto remote repository, and changing the old migration file again will hurt other developers productivity. In case of any confusion, always create a new migration:
rails generate migration add_reset_sent_to_users reset_sent_at:datetime
I think it depends what state your rails app is in.
If you were working on a production app then editing migrations is not advisable due to data loss and changes should be made with a new migration.
If your working locally in development then I would edit the migration directly and add the missing column and rerun your migration.
Don't be worried about editing you migrations, just remember to rake db:rollback the migration you are editing before making changes or you will encounter errors.
This is where changing your migration from:
def change
add_column('users', 'reset_digest', :string)
add_column('users', 'reset_sent_at', :datetime) # Would have to perform rollback before adding this line
end
to:
def up
add_column('users', 'reset_digest', :string)
add_column('users', 'reset_sent_at', :datetime) # Added after migration
**rake db:migrate
end
def down
remove_column('users', 'reset_digest', :string)
remove_column('users', 'reset_sent_at', :datetime) # Add this after rollback
**rake db:rollback
end
Allows you to make changes to your migrations before you rake db:rollback
This requires a bit more code but I find it easier when I'm building a new app and things are changing frequently.
The problem is the following:
I have db/seed.rb full of initial data.
One of migrations depends on data this seed provides.
I'm trying to deploy my app from empty db.
Result is:
RAILS_ENV=production rake db:migrate - fails due to lack of initial data
RAILS_ENV=production rake db:seed - fails due to pending migrations
I wanted to somehow tell rake to ignore pending migrations, but unable to do it so far.
UPDATE (due to additional experience)
Sometimes migrations and model code goes out of sync, so migrations are not being run.
To avoid this problem recently used redefining of model in migrations:
# reset all callbacks, hooks, etc for this model
class MyAwesomeModel < ActiveRecord::Base
end
class DoSomethingCool < ActiveRecord::Migration
def change
...
end
end
I am not very sure if this will help you. But I was looking for something and found this question. So it looks like this might help:
In RAILS_ROOT/config/environments/development.rb
Set the following setting to false:
# NOTE: original version is `:page_load`
config.active_record.migration_error = false
In my situation it now does not show the pending migration error anymore. Should work for rake tasks and console for the same environment as well.
Source in rails/rails
Rename the migration dependent on the data from:
20140730091353_migration_name.rb
to
.20140730091353_migration_name.rb
(add a dot at the start of the filename)
Then run rake db:seed (it will no longer complain on the pending migrations) and then rename back the migration.
If you have more migrations following after, you have to rename all of them or just move it temporary away.
Rails stores migration information in a table called schema_migrations.
You can add the version from your migration into that table to skip a specific migration.
The version is the number string which comes before the description in the file name.
[version]_Create_Awesome.rb
I had a similar issue. I commented out the add_column lines and ran the rake db:migrate commands and then removed the comment when I will need it for the testing or production environment.
There is no way unless you monkey patch the Rails code. I strongly advise you to fix your migrations instead.
A migration should not depend on the existence of some data in the database. It can depend on a previous migration, but of course absolutely not on the data on the db.
If you came across the "pending migrations" issue when trying to seed your data from within a running Rails application, you can simply call this directly which avoids the abort_if_pending_migrations check:
ActiveRecord::Tasks::DatabaseTasks.load_seed
See where seeds are actually called from within ActiveRecord:
https://github.com/rails/rails/blob/v6.0.3.2/activerecord/lib/active_record/railties/databases.rake#L331
and see the DatabaseTasks docs:
https://apidock.com/rails/v6.0.0/ActiveRecord/Tasks/DatabaseTasks
https://apidock.com/rails/v6.0.0/ActiveRecord/Tasks/DatabaseTasks/load_seed
I have a question regarding my migrations in rails.
Normally when i want to add a colum to a model for i dont make extra migrations but instead i perform this steps:
rake db:rollback
next i change the migration file in db/migrations and rerune:
rake db:migrate
The biggest problem is that when i do this i loose my data.
Previous i wrote migrations from the command line with for example
rake g migration Add_Column_House_to_Users house:string
The problem with this approach is that my db/migrations folder afterwards get very large and not very clear! I mean at the end i dont know wich variables the object has! Im not an expert in rails and would like to ask you how to keep the overview over the migrations!Thanks
Just a minor thought - I just use the file db/migrate/schema.rb to determine whats in the database as opposed to tracking through the migrations
You definitely shouldn't use db:rollback with a table with existing data.
I have a few production RonR apps with a ton of data and there are 100+ entries in the migrations table and adding new migrations to tweak tables is the rails way to do things. Not sure what you mean by lucid, but your schema and data model are going to change over time and that is ok and expected.
One tip. The migrations are great, but they are just the beginning, you can include complex logic as needed to fix your existing data (like so)
Changing data in existing table:
def up
add_column :rsvps, :column_name_id, :integer
update_data
end
def update_data
rsvps = Rsvp.where("other_column is not null")
rsvps.each do |rsvp|
invite = Blah.find(rsvp.example_id)
...
rsvp.save
end
end
Another tip: backup your production database often (should do this anyway), but use it to test all of your migrations before deploying. I run scripts like this all the time for local testing:
mysql -u root -ppassword
drop database mydatabase_dev;
create database mydatabase_dev;
use mydatabase_dev;
source /var/www/bak/mydatabase_backup_2013-10-04-16.28.06.sql
exit
rake db:migrate
New to Rails here. Couple of questions about migrations:
I created a migration that I no longer want. I want to remove it. Is the correct command simply rails destroy migration AddMyColumnToMyModel ?
Let's say I mistype that migration name that I want to destroy... Here's what happens when I attempt to destroy a migration that does not exist.
$ rails destroy migration Blah
invoke active_record
remove migration.rb
It says it's removing migration.rb... Is this a bad thing?
Sure, that's the right command. Just be careful: if you actually ran the unwanted migration by using rake db:migrate to commit the changes to your database, be sure to run this before anything else:
rake db:rollback
What that does is run the down method on your latest migration. It does absolutely the same thing as:
rake db:migrate:down VERSION=20130529014413
Where the version number corresponds to that of your latest migration. It can also take a STEP parameter in case you need to roll back a bunch of migrations instead of only one, like so:
rake db:rollback STEP=3
Of course, if you just generated your unwanted migration and never ran it, there's no need to roll anything back. You can use the command you posted or manually delete the corresponding file to get rid of it.
Source: http://guides.rubyonrails.org/migrations.html#rolling-back
Don't worry, that's not doing anything to your code.
I have a table that I created using the migrations, now I want to get rid of this table. I'm pretty sure I can just back out that migration, but I can't find the syntax to do that. I found this question from searching Rails DB Migration - How To Drop a Table?
but he basically says you can find what you need and provides a link. I read that link and I didn't see anything that says how to do it. I saw pieces of it, but I don't know how to put them together.
I see in the migration it has a self.down method, I really just need to know how to call that.
Try to create an empty migration and use:
drop_table :table_name
You can rollback the last migration with:
rake db:rollback
That will run the self.down method, which should be drop_table :table_name
rake db:rollback STEP=n
where n is the number of steps you need to roll back. If you leave the STEP off it just rolls back 1.
To migrate to a particular version, use:
rake db:migrate:down VERSION=20080906120000
If you want to quickly apply a table drop, you could create a new migration, run it, then delete it along with the original migration you no longer want. The syntax for dropping a table is:
drop_table :table_name
Destroying the model is not the best way.
Instead, run this command in your rails console: rake db:rollback
(to access the rails console, type rails c in a terminal as shown here)
You can remove a table using rake to destroy the model:
rails destroy model your_model