I am following the rails tutorial videos and I can't figure out what the db:test:prepare command actually does. Can someone provide an explanation?
The rake db:migrate above runs any pending migrations on the
development environment and updates db/schema.rb. The rake
db:test:load recreates the test database from the current
db/schema.rb. On subsequent attempts, it is a good idea to first run
db:test:prepare, as it first checks for pending migrations and warns
you appropriately.
-- http://guides.rubyonrails.org/testing.html
Basically it handles cloning the database so you don't have to run the migrations against test to update the test database.
Specifically, rake db:test:prepare will do the following:
Check for pending migrations and,
load the test schema
That is, it will look your db/schema.rb file to determine if any migrations that exist in your project that have not been run. Assuming there are no outstanding migrations, it will then empty the database and reload it based on the contents of the db/schema.rb file.
rake db:test:prepare is a good solution for PG issues like this.
“PG::UndefinedTable: ERROR: relation does not exist” with a correct Rails naming and convention" where I couldn't just execute rake db:migrate RAILS_ENV=production
When, for example you can't create test database for a bug discussed here: "PG undefinedtable error relation users does not exist"
All arround this error
"PG::UndefinedTable: ERROR: relation xxxxx does not exist”
Related
I am trying to run a rails server and am coming across this error:
Migrations are pending. To resolve this issue, run: bin/rake db:migrate RAILS_ENV=development
The DB in question is currently empty so no worries of losing data. When I run the code:
bundle exec rake db:migrate
RAILS_ENV=development rake db:migrate
rake db:migrate
I am returned the error:
rake aborted!
ActiveRecord::DuplicateMigrationNameError:
Multiple migrations have the name CreatePosts
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
When running the server, this is returned to my terminal:
Started GET "/" for ::1 at 2015-09-22 11:30:34 -0400
ActiveRecord::PendingMigrationError (
Migrations are pending. To resolve this issue, run:
bin/rake db:migrate RAILS_ENV=development
):
And finally, running rake db:migrate:status returns:
Schema migrations table does not exist yet.
What could possibly be going on? Any help is greatly appreciated!
Output of migrate:status after bin/rake command
Status Migration ID Migration Name
--------------------------------------------------
up 20150922142819 Devise create users
up 20150922143253 Create posts
down 20150922143414 Create posts
down 20150922145906 Acts as votable migration
down 20150922150209 Create comments
down 20150922151035 Acts as follower migration
You must create the database schema/structure before you run migrations. db:schema:load will do this for you:
bin/rake db:schema:load
As for the error "Multiple migrations have the name CreatePosts" - it's as it says. Look in the contents your db/migrate folder for two files that have the same name class CreatePosts within the files - they should be named differently, or the second one should be removed if they are duplicates.
It seems like you have more than one migration with the same name. This is not allowed. If your database is empty, no tables, the best plan is to rename the second one so they don't conflict any more.
Obviously the filenames are unique, but each migration file defines a class, and these classes must be unique as well, plus should match the filename.
Having 201509201949343_create_posts and 201509220293910_create_posts would be a typical conflict here.
You may want to investigate how this came to pass, as having your development schema diverge from the production one is generally a bad idea. Once you resolve the conflict locally, try and update the schema tracking table on production accordingly.
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...)
Is there a quick rake db:rollback command for all of the migrations?
Rolling back all migrations
To rollback all migrations the best solution is the one #Claudio Floreani proposed:
rake db:migrate VERSION=0
This will rollback every migration. You can read why this is the best approach in his answer. Then, run all migrations again with
rake db:migrate
Resetting the database
Reset
rake db:migrate:reset #runs db:drop db:create db:migrate
This method drops the database and runs the migrations again.
Loading the last schema
rake db:reset
This method will drop the database and load the data from the last schema.
You can see more information in this post: Difference between rake db:migrate db:reset and db:schema:load
Thanks to #Claudio Floreani and all the users who commented to improve the answer.
If you really want to rollback all of the migrations, and not just take the database to a pristine state or to the last schema, you have to run:
rake db:migrate VERSION=0
This will actually rollback all the way down every migration and ensure that every migration is reversible.
If you now issue
rake db:migrate:status
you will see that all the migrations are still there but they are in a 'down' (not applied) state.
Other commands that imply a rake db:reset or rake db:drop (such as in the answers by #Orlando or #Alex Falke) won't do any rollback at all: that is, they won't ensure that every migration is reversible.
Moreover, rake db:drop cannot be run while the database is being accessed by other users, while rollbacks can be performed live (even if this is generally not recommended). And last but not least, simply dropping and recreating the database will also delete the schema migrations table: if someone runs rake db:migrate:status after the database has been dropped, he will be replied with "Schema migrations table does not exist yet" and will have no clues about which migrations can be applied (unless he knows it yet or can list them).
just use rake db:reset, that will drop your database (same as undoing all migrations) and reset to the last schema.
UPDATE: a more correct approach will be using rake db:migrate:reset. That will drop the database, create it again and run all the migrations, instead of resetting to the latest schema.
If a permission problem raises (like it happened to me), maybe you could try dropping all database tables like I did with rubymine (just open database tool window, select all tables and right-click -> drop), it should be similar with other IDEs. Some tables like sqlite_master and sqlite_sequence were conveniently ignored in the drop.
This allowed me to do
rails db:migrate
and everything worked fine. Of course you loose all data!
I know that I can run specific migrations:
rake db:migrate:up VERSION=20080906120000
But can I run a specific migration against my test database? Will the following work?
RAILS_ENV=test rake db:migrate:up VERSION=20080906120000
In theory, running the migrations in default mode (which should affect the development database) and then running rake db:test:prepare should get the job done, but I found something strange with my test database after doing that, and I need to run a specific migration on the test database to aid my troubleshooting.
I'd just try out the above rake command, except I'm in the middle of a long data seeding run on my development database, and I can't risk the migration interfering with that, so I figured I'd see if anyone knows the answer before I can determine it myself. :)
In different order:
rake db:migrate:up VERSION=20080906120000 RAILS_ENV=test