I have a small Ruby on Rails app, and I made a mistake creating a model and so on.
How can I fully delete its database? Not reseting migrations or dropping its tables, but to delete all db related files? (schema.rb, etc)
To drop database
rake db:drop
Then for creating database
rake db:create
For migrations
rake db:migrate
For seed
rake db:seed
Deleting these files will not remove the database from your system. You should never delete your schema.rb because it holds the structure of your database. (And not the database records themselves.) If you simply created a new model, Rails does not automatically create a database table (that's what migrations do).
If you still want to drop your entire database (the structure and data), this is the command you need (found when calling rake -T)
rake db:drop # Drops the database from DATABASE_URL or
# config/database.yml for the current RAILS_ENV
# (use db:drop:all to drop all databases)
By default, RAILS_ENV is not set. If you called rake db:drop during this state, all databases associated with this app will be dropped. In order to drop, say, only development:
export RAILS_ENV=development
rake db:drop
You can do the same with test and production environments.
Related
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...)
I am very new in ruby-on-rails. I have doubt in rake. create function is create a new db. After that, we want to run some commands like
rake db:load
rake db:data:load
rake db:schema:load
rake db:migrate
rake db:seed
But why we want to run this cmds after create the db and what function of the about cmd.
Thanks for your advice.
You can use rake -T to get the description of each task:
$ rake -T | grep db
rake db:create # Create the database from config/database.yml for the current Rails.env (use db:create:all to create all dbs in the config)
rake db:drop # Drops the database for the current Rails.env (use db:drop:all to drop all databases)
rake db:fixtures:load # Load fixtures into the current environment's database.
rake db:migrate # Migrate the database (options: VERSION=x, VERBOSE=false).
rake db:migrate:status # Display status of migrations
rake db:rollback # Rolls the schema back to the previous version (specify steps w/ STEP=n).
rake db:schema:dump # Create a db/schema.rb file that can be portably used against any DB supported by AR
rake db:schema:load # Load a schema.rb file into the database
rake db:seed # Load the seed data from db/seeds.rb
rake db:setup # Create the database, load the schema, and initialize with the seed data (use db:reset to also drop the db first)
rake db:structure:dump # Dump the database structure to db/structure.sql. Specify another file with DB_STRUCTURE=db/my_structure.sql
rake db:version # Retrieves the current schema version number
I this what you were asking about?
EDIT:
You can read more about what migrations are for here: http://guides.rubyonrails.org/migrations.html
EDIT 2:
rake db:migrate allows you to update the DB schema in a "sane" way: you can create a new migration (read the guides!) and add a new column for example, add an index, rename a column, etc. - migrations allow you to "travel" back and forth in "time" - you can run the migration and rollback it later.
When you generate a new migration:
$ rails g migration add_new_column_to_some_table you will be able to run rake db:migrate later on to apply to changes you want (of course you have to write the body of this generated migration).
I STRONLY advise you to read the guides though :)
EDIT 3:
add_column :users, :price, :float, for example, will add price column to the users table, the type of the column will be float (float isn't a best idea to store money related things BTW!). This column will be NULL by default.
EDIT 4:
Information about which migrations were run is stored in schema_migrations table: running migration for the first time will add a new record in this table with version of this migration (date + some random numbers from the name of the file). Rollbacking a migration will remove this record. Running a migration twice will not have any effect.
Simply put, db:migrate doesn't destroy existing data you have in your database. so running migrations and that rake task allows your data to exist from changes you make.
Workflow in words
You create an empty data base.
You will want to add a table of data for your first model into the database. This is done by editing a file in db/migrate
Now you want a second model, so you create your model and edit the migration file in db/migrate that was created for you
The easiest way to update your database without destroy any of the existing data, is to run bundle exec rake db:migrate. This adds the contents of the second migration file into the db and won't hurt existing data.
Example workflow after creating a project:
bundle exec rake db:create:all
bundle exec rails generate scaffold Users name:string email:string
bundle exec rake db:migrate
At this stage, bundle exec rails s and go to localhost:3000/users/new and create a new user.
bundle exec rails generate scaffold Posts title:string body:text
bundle exec rake db:migrate
Back in your browser go to localhost:3000/users and you should still see the user you created.
Due to some deployment issues I stopped tracking schema.rb in git. Somehow I have stuffed this up and somewhere along the way my schema.rb file has disappeared.
Is there a way of regenerating schema.rb from the database or from the migrations? I would prefer not to lose the existing data.
If you run a rake -T it will list all possible rake tasks for your Rails project. One of them is db:schema:dump which will recreate the schema.rb for the Rails app from the database.
bundle exec rake db:schema:dump
Careful,
rake db:schema:dump
will dump the current DB schema FROM the DB. This means that if you made any changes to your migrations, they will NOT be reflected in schema.rb file which is not what you want IMO.
If you want to re-create the schema from the migrations, do the following:
rake db:drop # ERASES THE DATABASE !!!!
rake db:create
rake db:migrate
RAILS 5 Way:
rails db:schema:dump
or if you Encounter Gem::LoadError then:
bundle exec rails db:schema:dump
Note:
in rails 5 it is recommended that task are generated/executed by using rails instead of rake, this is just to remember, rails generated task are of extension .rake see in lib/tasks/myTask.rake. which means these task can also be executed by prepending rake.
rake db:schema:dump
I think this is still valid in Rails 3 - it regenerates the schema.rb from the database.
Directly from the schema.rb file itself:
If you need to create the application database on another
system, you should be using db:schema:load, not running all the migrations
from scratch. The latter is a flawed and unsustainable approach (the more migrations
you'll amass, the slower it'll run and the greater likelihood for issues).
So do NOT do the suggestion of rake db:migrate, which was suggested in the - at the time of this writing - lowest rated answer.
If you regenerate schema.rb locally, you should be alright. It simply holds a representation of the structure of your database tables. The data itself is not contained in this file.
To regenerate your schema.rb file, run:
bundle exec rake db:schema:dump
Then simply commit the new schema.rb file and you should be in good shape!
I also had a similar problem where my old schema was not refreshing even if I deleted migration.
So, what I did was dropping all existing tables in the database and migrating them again. Then running "db:schema:load" command gave me a fresh schema.rb.
drop table my_table_name // deleted them individually
rake db:migrate
rake db:schema:dump // re-created a new schema
I tried to run:
rake db:migrate VERSION=0
It reverts all migrations except the last one.
Then I tried to run:
rake db:migrate:down VERSION=<timestamp_of_last_migration>
but it didn't revert either. Why ?
Is there a command that runs all down methods at once ?
If your database only related to this project, and you are trying to undo everything in your migrations, I'd simply drop the database, and then run rake db:create.
Then you have an empty database ready to go.
Or is there another reason you're trying to run the down scripts?
You could check this list.
Maybe this could help you
rake db:create[:all]: If :all not specified then create the database defined in config/database.yml for the current RAILS_ENV. If :all is specified then create all of the databases defined in config/database.yml.
rake db:fixtures:load: Load fixtures into the current environment's database. Load specific fixtures using FIXTURES=x,y
rake db:migrate [VERSION=n]: Migrate the database through scripts in db/migrate. Target specific version with VERSION=n
rake db:migrate:redo [STEP=n]: (2.0.2) Revert the database by rolling back "STEP" number of VERSIONS and re-applying migrations.
rake db:migrate:reset: (2.0.2) Drop the database, create it and then re-apply all migrations. The considerations outlined in the note to rake db:create apply.
rake db:reset: Drop and re-create database using db/schema.rb. The considerations outlined in the note to rake db:create apply.
rake db:rollback [STEP=N]: (2.0.2) Revert migration 1 or n STEPs back.
rake db:schema:dump: Create a db/schema.rb file that can be portably used against any DB supported by AR
rake db:schema:load: Load a schema.rb file into the database
rake db:sessions:clear: Clear the sessions table
rake db:sessions:create: Creates a sessions table for use with CGI::Session::ActiveRecordStore
rake db:structure:dump: Dump the database structure to a SQL file
rake db:test:clone: Recreate the test database from the current environment's database schema
rake db:test:clone_structure: Recreate the test databases from the development structure
rake db:test:prepare: Prepare the test database and load the schema
rake db:test:purge: Empty the test database
there is another way:
rake db:rollback STEP=100
this will revert last 100 migrations
taken from http://guides.rubyonrails.org/migrations.html#rolling-back
try:
rake db:migrate:down VERSION=<timestamp_of_first_migration>
this will run the self.down for your first migration, essentially wiping everything out. at least, it just did for me!