Is advisable to do a rake db:rollback when I am wrong in a field of the database; then a rake db:migrate to create the correct structure of the database?
In development environment that might be an option.
But as soon as you pushed the migration to a remote repository and another developer ran that migration against his database or the migration ran on staging or production, you should not change the migration anymore.
Instead, add just new migration in such cases.
Related
I initially ran a migration when I created the database and everything worked fine. Then I went and deleted the table in postgresql manually. Now when I run rake db:migrate, it runs but doesn't create the table.
It depends on what your migrations do. rake db:migrate can create or change tables, depending on your definitions. To setup the database and the tables in the beginning you can use rake db:schema:load or rake db:setup. rake -T gives an overview over all available rake tasks.
Database migrations are stored in the table schema_migrations which has one column version. As long as the version of the migration in question can be found here, the migration is not executed again.
I'm currently following the ruby on rails tutorial: http://guides.rubyonrails.org/getting_started.html.
I am trying to save data into the database. However, when I run: rails server I get the following error:
Migrations are pending. To resolve this issue, run: bin/rake db:migrate RAILS_ENV=development
I've looked at the other articles and when I run:
bin/rake db:migrate
I get a rake aborted!
After running:
rake db:abort_if_pending_migrations....
I see that:
You have 1 pending migration:
20150805200129 CreateDatabases
SQLite3::SQLException: table "databases" already exists:
and it just tells me to run rake db:migrate to start again.
It seems that it already exists. Is there a way to cancel the pending migration?
Sometimes, even dropping a local development database is not a good idea.
There are better ways to delete/destroy a specific migration in your Rails application.
You could use rails d migration command to destroy a particular migration:
rails d migration MigrationName
To undo the changes corresponding to a particular migration, you can use db:migrate:down method like this:
rake db:migrate:down VERSION=XXX
Sometimes, things could get more messy and in those situation another handy thing is to take a look at the schema_migrations table in your database which has all the migrations with their version saved in it.
You can delete a particular migration from this table like this:
delete from schema_migrations WHERE version = VERSION;
if you don't want that migration to be present anymore.
Your migration may have failed midway (so it created the table, but didn't finish).
You are just using development environment, so it's okay to just drop the database and rebuild it from scratch:
rake db:drop # THIS WILL DELETE YOUR DATABASE
rake db:create
rake db:migrate
If you are like me and maintain your database structure outside of Rails, you can just delete the migration file from db/migration. I got the error in the OP's question when I used the rails generate command to create a model class, forgetting that it also creates a migration file.
Do not use this method if you rely on Rails to maintain your database structure!
I keep my Rails structure file up to date by building it from the database using:
bundle exec rake db:structure:dump
I do not encourage to drop the database and start from the beginning especially when you already have the data inside the database.
My approach to this will be migrate first, then rollback. After that you can safely delete the migration file. So the procedure is as following.
rails db:migrate
rails db rollback
rm db/migrate/your_last_migration_file.rb
You can recreate database and run all migrations in your development environment with such command
rails db:migrate:reset
If you want to revert the wrong migrations, You can drop the whole db using this:
rake db:drop
Then remove the migrations file manually(This wont corrupt the db when you recreate as the Schema migrations would be dropped as well).
Then run
rake db:migrate
And if there is data to be seeded, then run this as well
rake db:setup
I recently started using Rails, and created a few Models using the CLI which in turn created some migrations.
I ran the rake db:migrate command after adding all my columns in there, and then realized that I'd left out the associations.
So what did I do?
I went ahead and edited the migrations to include those keys.
I ran rake db:migrate again, and nothing changed in the schema.
Then I ran rake db:reset and then rake db:setup.
When that didn't work, I deleted my schema.rb (the darn thing wouldn't get updated!) and tried recreating it. When I realized that didn't work, I dropped the database, and killed the schema.
Now I'm stuck with some manually modified migrations, no schema.rb and no database.
How do I get the modified migrations to generate a schema, and play nice with Rails?
In development it does not matter to drop and rebuild your database. I do it often and I even have a rake task for that. The 3 command to chain are:
rake db:drop
rake db:create
rake db:migrate
# And a 4rth optional command to rebuild your test database
rake db:test:prepare
With this you should be good
Next time you need to modify a migration manually after migrating it, you should process by:
rake db:rollback
edit your migration
rake db:migrate
Following those steps will save you some headaches
Bonus info:
After you deployed your migration to your production server you cannot manually modify it, hence you must write another migration that will perform the modification (adding columns, etc...)
Recently, after I deleted some manually created migrations that were named 99999999xxx_createwhatever, each migration I generate now start with 99999999999999xxx_etc
Any idea how to fix this so that they are generated like 2011xxxxxx again?
If you want to keep your data in database, use mysqldump to backup first.
Then reset your migration to version 0 rake db:migrate VERSION=0
Make sure there isn't any 99999999x migration file, then run rake db:migrate
Finally, restore your database.
I would like to remove/delete a migration file. How would I go about doing that? I know there are similar questions on here but as an update, is there a better way than doing script/destroy?
Also, should I do a db:reset or db:drop if I remove/delete a migration?
I usually:
Perform a rake db:migrate VERSION=XXX on all environments, to the version before the one I want to delete.
Delete the migration file manually.
If there are pending migrations (i.e., the migration I removed was not the last one), I just perform a new rake db:migrate again.
If your application is already on production or staging, it's safer to just write another migration that destroys your table or columns.
Another great reference for migrations is: http://guides.rubyonrails.org/migrations.html
Another way to delete the migration:
$ rails d migration SameMigrationNameAsUsedToGenerate
Use it before rake db:migrate is executed because changes in database will stay forever :) - or remove changes in Database manually
Run below commands from app's home directory:
rake db:migrate:down VERSION="20140311142212" (here version is the timestamp prepended by rails when migration was created. This action will revert DB changes due to this migration)
Run "rails destroy migration migration_name" (migration_name is the one use chose while creating migration. Remove "timestamp_" from your migration file name to get it)
None of these answers quite fit the problem i had as the migration i wanted to delete was missing:
I had created and run a migration in some other branch, which was then discarded. The problem is when a migration is run, rails adds the version into a schema_migrations table in the database. So even if it isn't listed in your db structure or schema, rails looks for it.
You can reveal these orphaned migrations by running:
rails db:migrate:status
Note the versions of the missing migrations and head into the db console:
rails dbconsole
Now remove the versions from the migration table manually:
delete from schema_migrations where version='<version>';
You should now be good.
You can also run a down migration like so:
rake db:migrate:down VERSION=versionnumber
Refer to the Ruby on Rails guide on migrations for more info.
We can use,
$ rails d migration table_name
Which will delete the migration.
Sometimes I found myself deleting the migration file and then deleting the corresponding entry on the table schema_migrations from the database. Not pretty but it works.
This also works in Rails 5.
If the migration was the most recent one you can remove the database column(s) that the migration added by doing:
rake db:rollback
then remove the migration file itself by running:
rails d migration WhateverYourMigrationWasNamed.rb
Look at 4.1 Rolling Back
http://guides.rubyonrails.org/migrations.html
$ rake db:rollback
I just had this same problem:
rails d migration fuu
-this deleted the migration with the last timestamp
rails d migration fuu
-this deleted the other migration
use git status to check that is not on the untracked files anymore
rails g migration fuu
That fixed it for me
Side Note:
Starting at rails 5.0.0
rake has been changed to rails
So perform the following
rails db:migrate VERSION=0