I'm beginner in Ruby on Rails. I dropped my table. But I have the files in the db/migrate folder. How can I get back my table from those migrate files?
The ideal way to do this, is using
rake db:setup
This will recreate the database and load the schema into the development database. With every migration rails keeps the current state of the database in schema.rb (or structure.sql), and it uses those to efficiently recreate the last state.
If you have pending migrations, you will have to do rake db:migrate, but this will take more time, since it will redo every step as before.
Also note in some cases it is not possible to run the migrations from the start again, and imho that is not the intention of the migrations.
Run rake db:migrate to get it back.
According to this question, you should be able to do the following:
rake db:create #-> creates DB based on the schema file
rake db:migrate #-> populates the db with the various changes in the migrations
If you follow these steps, with nathanvda's advice, you should be able to solve the issue you're seeing!
Related
I have unseen duplicate relations and tables and I am trying to destroy my entire DB and reset out of pure frustration, and I can't even do that. When I run rake db:drop or reset, everything is still there in my schema and migrations. How do I kill this entire DB and build it over again?
While they are closely related, migration files/schema.rb are not the same thing as the database. rake db:drop doesn't delete the migration files or the schema because people may wish to easily recreate their entire database while maintaining the information on how the database was built (ie the migration files).
If you want to start from scratch, drop the database rake db:drop and manually delete the migration files (schema will be overwritten when you create your new migrations).
If you do
rake db:rollback STEP=100
That will revert the last 100 migrations (so take you to zero state)
I currently have a few migrations which were created when I initially created models using rails generate model. I've run those migrations and successfully updated the database.
I've then made some changes to these migrations (not added new ones) because they were very small changes like a new column, or making a column unique, or adding an index.
But, even when I reset my db and run all migrations again, rails is insisting on using an outdated schema.rb file.
What should I be doing? How do I force a reload of this schema.rb?
Provided you haven't pushed the code to production you can run rake db:rollback then rake db:migrate to drop and recreate the tables.
Use this:
rake db:drop db:create db:migrate
On my server when deploying the app for the first time, I ran rake db:setup which loads my entire migration history from schema.rb. Now I have more stuff I want to add, but when I run rake db:migrate on my server I realize it's trying to run my very first migration, which is failing since the table obviously exists.
Examining the schema_migrations table on my production server, I realize it only has one entry in it, which is the migration that was the most current at the time of the initial deployment. Isn't it supposed to have the entire migration history in it? If so, what caused this? If not, why is it doing this?
Did you remember to migrate within the production environment?
rake db:migrate RAILS_ENV=production
I don't know how this happened, but the problem was indeed the fact that the schema_migrations table only contained the timestamp of the most recent migration as opposed to the full history. I manually inserted all of them and it worked fine.
What scares me is that this somehow happened and I don't know how. Oh well.
Does rake db:migrate only add new migrations, or does it drop all migrations/changes and build everything new?
I think rake is throwing an error because it is trying to access a table attribute in migration 040 that was deleted in migration 042. somehow my DB and rake are out of synch and I want to fix them.
for you experts out there - is it common for rake to get out of synch with migrations? how can I avoid this (no, I do not hand-edit my schema or rake files).
When you use rails migrations, a table called schema_migrations is automatically created, which keeps track of what migrations have been applied, by storing the version number of each migration (this is the number that prefaces the migration name in the file name, ie db/migrate/_20090617111204__migration.rb). When you run rake db:migrate to migrate up, only migrations which have not been run previously (ie. their version is not contained in the table) will be run (for this reason, changing a migration that's already been executed will have no effect when running db:migrate). When migrating down, all versions found in schema_migrations that are greater than the version you are rolling back to will be undone.
Everytime you create a migration using scripts (like script/generate model ...) a new migration is added to the correct directory ready to be synched with the real database.
Actually rake db:migrate just checks which missing migrations still need to be applied to the database without caring about the previouse ones.
Of course if you modify the database using other ways is common to obtain out-of-synch things because as you said you can find yourself applying a migration to something that is changed underneath.
A migration means that you move from the current version to a newer version (as is said in the first answer). Using rake db:migrate you can apply any new changes to your schema. But if you want to rollback to a previous migration you can use rake db:rollback to nullify your new changes if they are incorrectly defined. Caution: by doing so your data will be lost.
i have a bug in a "self.drop" in a migration such that I cannot roll back past that migration. how can i start from scratch and build up from migration 001? also, is there a way to do this without losing my data (it's just testing, but still...)
You can comment all statements in self.down migration and rollback to previous db version.
Then apply changes by hand using a gui/web db client to match db schema before migration.
After you will be able to run migration again and your data will not be lost.
rake db:drop
rake db:create
rake db:migrate
It will reset your database and run all migrations. If you don't want to lose your data you can save it using plugin yaml_db:
rake db:data:dump # stores all data in db/data.yml
...
rake db:data:load # loads db/data.yml to database
If you have an error in a migration you can edit it and then try to rollback.
I realise this is an old question, but imho still relevant. If you want to recreate your database from scratch, one does not rollback and rerun migration, one just does
rake db:setup
This will drop, create and fill the database with the current combined state of all the migrations. This is because, definitely in a large system, running all the migrations might no longer work. However, running the schema.rb will always work.
My advice would also be to avoid rollback of migrations as much as possible, unless when you just created a migration and want to make some addition/typo/fix, before having pushed the migration to your team or any deployment.