Is there a way to destroy all records in my database in one line, without specifying my models?
Say I have three models User Picture Post. I can call User.all.destroy_all etc, but can I collect all records without specifying the models themselves?
As Sebastian Palma says you can do the rake task rake db:reset which will drop and setup your database.
Alternatively you can get all the descendants of ActiveRecord. If you're in development mode you'll need to eager_load first.
Rails.application.eager_load!
Then you could do
ActiveRecord.descendants.each(&:destroy_all)
PLEASE BE EXTREMELY CAREFUL! THE ABOVE WILL DELETE ALL RECORDS IN YOUR DATABASE TABLES!
Related
I have a join table in rails that has a few entries that need to be deleted.
lets say the join table is named 'products_variants'
I found out i have a few entries in this join table that were created erroneously a while ago. I have their IDs, so i could go in phpmyadmin and delete them, but I want to make a migration to do it in case anyone uses an older database (which has happened before).
Since I don't have a ruby object representing this join table I cant do something like:
ProductsVariants.find(id_array)
How would i go about deleting these entries in a rails migration?
You can create AR class for this table inside of migration and use it for delete record.
How would you do it from the console? Whatever that is, put it in the migration. For example
class Cleanup < ActiveRecord::Migration
def up
execute("delete from product_variants where id in (1,2,3)")
end
def down
end
end
Barring a solution like maxd's answer, you can also delete them via plain 'ol SQL. If you already have the list of ids, you can do something like this:
ActiveRecord::Base.connection.execute("DELETE FROM products_variants WHERE id IN (...)")
Where ... is the list of ids to delete.
Semi-pointless side-note: Technically speaking, data manipulation is not typically done in the migrations for various reason; one of them being that you're usually not necessarily guaranteed that all (or even any) migrations will be run by your colleagues (speaking very generally here), or in the case of new local project setups (meaning, you've just pulled down the project code and are setting it up locally for the first time).
While it doesn't sound like this is an issue in your scenario, if you want to do this the Rails-y way, one alternative would be to put this in a Rake task, so that you or others can execute it as needed, rather than relying on the migrations.
I'm new to rails and I haven't been able to find a definitive answer to this question.
Let's say I have
Project.create!([{title: "foo", description: "bar"}])
in my seeds.rb file and then run
$rake db:seed
twice. Would there be two near-identical entries in the database or would it override the initial entry?
It will duplicate.
If you want to run multiple times, but prevent duplication. I guess you could:
Use validation in one key field like putting validate_uniqueness_of :key_attribute
Test the count of your table like:
MyClass.create if MyClass.count == 0
Better solution might be to use find_or_create_by method. See the docs: http://easyactiverecord.com/blog/2014/03/24/using-find-or-create-with-multiple-attributes/
It just runs the file. Rails does nothing for you, as far as preventing creation of duplicate seed data. If your file creates a record, it will attempt to create that record each time you seed. It's completely up to you to prevent this, in the case that you don't want duplicate seed data.
If you want to create a record unless it already exists, use find_or_create_by:
Project.find_or_create_by_title_and_description "foo", "bar"
This will create a Project with the given title and description unless it already exists, letting you run rake db:seed as many times as you want without creating duplicates.
I'm a junior Rails developer and at work we faced the following problem:
Needed to update the value of a column only for one record.
What we did is creating a migration like this:
class DisableAccessForUser < ActiveRecord::Migration
def change
User.where(name: "User").first.update_column(:access, false)
end
end
Are migrations only for schema changes?
What other solutions do you suggest?
PS: I can only change it with code. No access to console.
The short version is, since migrations are only for schema changes, you wouldn't want to use them to change actual data in the database.
The main issue is that your data-manipulating migration(s) might be ignored by other developers if they load the DB structuring using either rake db:schema:load or rake db:reset. Both of which merely load the latest version of the structure using the schema.rb file and do not touch the migrations.
As Nikita Singh also noted in the comments, I too would say the best method of changing row data is to implement a simple rake task that can be run as needed, independent of the migration structure. Or, for a first time installation, the seed.rb file is perfect to load initial system data.
Hope that rambling helps.
Update
Found some documentation in some "official" sources:
Rails Guide for Migrations - Using Models in your Migrations. This section gives a description of a scenario in which data-manipulation in the migration files can cause problems for other developers.
Rails Guide for Migrations - Migrations and Seed Data. Same document as above, doesn't really explain why it is bad to put seed or data manipulation in the migration, merely says to put all that in the seed.rd file.
This SO answer. This person basically says the same thing I wrote above, except they provide a quote from the book Agile Web Development with Rails (3rd edition), partially written by David Heinemeier Hansson, creator of Rails. I won't copy the quote, as you can read it in that post, but I believe it gives you a better idea of why seed or data manipulation in migrations might be considered a bad practice.
Migrations are fine for schema changes. But when you work on much collaborated projects like pulling code everyday from lot of developers.
Chances are you might miss some migrations(Value update migrations..No problem for schema changes) Because migrations depends on the timestamps.
So what we do is create a rake task in a single namespace to update some table values( Be careful it does not overwrites)
And invoke all the rake task in that NameSpace whenever we update the code from Git.
Making data changes using classes in migrations is dangerous because it's not terribly future proof. Changes to the class can easily break the migration in the future.
For example, let's imagine you were to add a new column to user (sample_group) and access that column in a Rails lifecycle callback that executes on object load (e.g. after_initialize). That would break this migration. If you weren't skipping callbacks and validations on save (by using update_column) there'd be even more ways to break this migration going forward.
When I want to make data changes in migrations I typically fall back to SQL. One can execute any SQL statement in a migration by using the execute() method. The exact SQL to use depends on the database in use, but you should be able to come up with a db appropriate query. For example in MySQL I believe the following should work:
execute("UPDATE users SET access = 0 WHERE id IN (select id from users order by id limit 1);")
This is far more future proof.
There is nothing wrong with using a migration to migrate the data in your database, in the right situation, if you do it right.
There are two related things you should avoid in your migrations (as many have mentioned), neither of which preclude migrating data:
It's not safe to use your models in your migrations. The code in the User model might change, and nobody is going to update your migration when that happens, so if some co-worker takes a vacation for 3 months, comes back, and tries to run all the migrations that happened while she was gone, but somebody renamed the User model in the mean time, your migration will be broken, and prevent her from catching up. This just means you have to use SQL, or (if you are determined to keep even your migrations implementation-agnostic) include an independent copy of an ActiveRecord model directly in your migration file (nested under the migration class).
It also doesn't make sense to use migrations for seed data, which is, specifically, data that is to be used to populate a new database when someone sets up the app for the first time so the app will run (or will have the data one would expect in a brand new instance of the app). You can't use migrations for this because you don't run migrations when setting up your database for the first time, you run db:schema:load. Hence the special file for maintaining seed data: seeds.rb. This just means that if you do need to add data in a migration (in order to get production and everyone's dev data up to speed), and it qualifies as seed data (necessary for the app to run), you need to add it to seeds.rb too!
Neither of these, however, mean that you shouldn't use migrations to migrate the data in existing databases. That is what they are for. You should use them!
A migrations is simply a structured way to make database changes, both schema and data.
In my opinion there are situations in which using migrations for data changes is legitimate.
For example:
If you are holding data which is mostly constant in your database but changes annually, it is fine to make a migration each year to update it. For example, if you list the teams in a soccer league a migration would be a good way to update the current teams in each year.
If you want to mass-alter an attribute of a large table. For example if you had a slug column in your user and the name "some user" would be translated to the slug "some_user" and now you want to change it to "some.user". This is something I'd do with a migration.
Having said that, I wouldn't use a migration to change a single user attribute. If this is something which happens occasionally you should make a dashboard which will allow you to edit this data in the future. Otherwise a rake task may be a good option.
This question is old and I think rails approach changed over time here. Based on https://edgeguides.rubyonrails.org/active_record_migrations.html#migrations-and-seed-data it's OK to feed new columns with data here. To be more precise your migration code should contain also "down" block:
class DisableAccessForUser < ActiveRecord::Migration
def up
User.where(name: "User").first.update_column(:access, false)
end
def down
User.where(name: "User").first.update_column(:access, true)
end
end
If you use seeds.rb to pre-fill data, don't forget to include new column value there, too:
User.find_or_create_by(id: 0, name: 'User', access: false)
If I remember correctly, changing particular records may work, but I'm not sure about that.
In any case, it isn't a good practice, migrations should be user for schema changes only.
For updating one record I would use console. Just type 'rails console' in terminal and input code to change attributes.
I want to try to apply a one to one relationship between two models inside Rails.
In modelX.rb file i added belongs_to :modelY. In modelY.rb file I added has_one :modelX
Does the database schema change automatically? Or do I need to run a command for this association to be committed?
Short answer: no
You can only use these methods (e.g. belongs_to) when you have made necessary changes ( usually with migrations ) in your data structure to support these relations.
The thing is that in Rails, usually, the database don't 'see' the relationship between the two entities with foreign keys and so on. The 'intelligence' of the relationships should be present on your models (as you already did using the belongs_to, has_one, etc).
Also, in order to have the schema changed you need to run the rake tasks for the database as,
rake db:migrate, db:rollback, etc.
For more information about this you can also check the
Rails guide
cheers.
In my Rails app development, When I run my Rspec test, I need to truncate all tables in my test database in after(:all) .
(That's to clean up all data in every table in test db)
To approach this, I am thinking to first get all ActiveRecord models which represent the tables in test db, then for each model, I use delete_all method to clean up each table. Thant's something like:
ALL_ACTIVE_RECORD_MODELS.each do |model|
model.delete_all
end
I have two questions to ask regards to this:
1. How to get all active record models in Rails in my rspec code?
2. Am I using a acceptable way to truncate all tables in my test DB or not? If not, what is the alternative way?
There is a gem to do exactly this task called database_cleaner: https://github.com/bmabey/database_cleaner.
It will make sure that everything is removed from your database however its default strategy is not to delete content but to use transactions and simply roll back the changes after each test.
Be warned that this can occasionally lead to a gotcha when testing behaviour that's intended to be transactional as you won't see your transaction execute. You can fix this by adding self.use_transactional_fixtures = false before any set of tests that you don't want to use transactions. Remember to clear your data away again afterward though.