rails-activerecord - w3toppers.com

How do you write a migration to rename an ActiveRecord model and its table in Rails?

Here’s an example: class RenameOldTableToNewTable < ActiveRecord::Migration def self.up rename_table :old_table_name, :new_table_name end def self.down rename_table :new_table_name, :old_table_name end end I had to go and rename the model declaration file manually. Edit: In Rails 3.1 & 4, ActiveRecord::Migration::CommandRecorder knows how to reverse rename_table migrations, so you can do this: class RenameOldTableToNewTable < ActiveRecord::Migration def change … Read more

How to skip ActiveRecord callbacks? [duplicate]

For Rails 3, ActiveSupport::Callbacks gives you the necessary control. I was just facing the same challenge in a data integration scenario where normally-desirable-callbacks needed to be brushed aside. You can reset_callbacks en-masse, or use skip_callback to disable judiciously, like this: Vote.skip_callback(:save, :after, :add_points_to_user) ..after which you can operate on Vote instances with :add_points_to_user inhibited

find vs find_by vs where

where returns ActiveRecord::Relation Now take a look at find_by implementation: def find_by where(*args).take end As you can see find_by is the same as where but it returns only one record. This method should be used for getting 1 record and where should be used for getting all records with some conditions.

Float vs Decimal in ActiveRecord

I remember my CompSci professor saying never to use floats for currency. The reason for that is how the IEEE specification defines floats in binary format. Basically, it stores sign, fraction and exponent to represent a Float. It’s like a scientific notation for binary (something like +1.43*10^2). Because of that, it is impossible to store … Read more

Add a reference column migration in Rails 4

Rails 4.x When you already have users and uploads tables and wish to add a new relationship between them. All you need to do is: just generate a migration using the following command: rails g migration AddUserToUploads user:references Which will create a migration file as: class AddUserToUploads < ActiveRecord::Migration def change add_reference :uploads, :user, index: … Read more

Rails 3 SQLite3 Boolean false

SQLite uses 1 for true and 0 for false: SQLite does not have a separate Boolean storage class. Instead, Boolean values are stored as integers 0 (false) and 1 (true). But SQLite also has a loose type system and automatically casts things so your ‘f’ is probably being interpreted as having a truthiness of “true” … Read more

Heroku Postgres Error: PGError: ERROR: relation “organizations” does not exist (ActiveRecord::StatementInvalid)

I had the same problem. To solve it, resetting the database is more easier. heroku rake db:reset (‘heroku run rake db:reset’ if you’re on cedar) heroku rake db:migrate (‘heroku run rake db:migrate’ if you’re on cedar) Then, migration was done successfully for my case 🙂 While this is a good solution in this context, don’t … Read more

LEFT OUTER JOIN in Rails 4

You can pass a string that is the join-sql too. eg joins(“LEFT JOIN StudentEnrollment se ON c.id = se.course_id”) Though I’d use rails-standard table naming for clarity: joins(“LEFT JOIN student_enrollments ON courses.id = student_enrollments.course_id”)

ActiveRecord Find By Year, Day or Month on a Date field

Assuming that your “date attribute” is a date (rather than a full timestamp) then a simple where will give you your “find by date”: Model.where(:date_column => date) You don’t want find_by_date_column as that will give at most one result. For the year, month, and day queries you’d want to use the extract SQL function: Model.where(‘extract(year … Read more

Rails – Nested includes on Active Records?

I believe the following should work for you. Event.includes(users: :profile) If you want to include an association (we’ll call it C) of an already included association (we’ll call it B), you’d use the syntax above. However, if you’d like to include D as well, which is also an association of B, that’s when you’d use … Read more