Overriding id on create in ActiveRecord

ruby-on-rails activerecord
Codebeef picture Codebeef · Jan 10, 2009 · Viewed 53.5k times · Source

Is there any way of overriding a model's id value on create? Something like:

Post.create(:id => 10, :title => 'Test')

would be ideal, but obviously won't work.

Answer

Jeff Dean picture Jeff Dean · Oct 2, 2009

id is just attr_protected, which is why you can't use mass-assignment to set it. However, when setting it manually, it just works:

o = SomeObject.new
o.id = 8888
o.save!
o.reload.id # => 8888

I'm not sure what the original motivation was, but I do this when converting ActiveHash models to ActiveRecord. ActiveHash allows you to use the same belongs_to semantics in ActiveRecord, but instead of having a migration and creating a table, and incurring the overhead of the database on every call, you just store your data in yml files. The foreign keys in the database reference the in-memory ids in the yml.

ActiveHash is great for picklists and small tables that change infrequently and only change by developers. So when going from ActiveHash to ActiveRecord, it's easiest to just keep all of the foreign key references the same.

Related questions

How to drop columns using Rails migration

What's the syntax for dropping a database table column through a Rails migration?

Read More
Rails: select unique values from a column

I already have a working solution, but I would really like to know why this doesn't work: ratings = Model.select(:rating).uniq ratings.each { |r| puts r.rating } It selects, but don't print unique values, it prints all values, including …

Read More
Rails: How do I create a default value for attributes in Rails activerecord's model?

I want to create a default value for an attribute by defining it in ActiveRecord. By default everytime the record is created, I want to have a default value for attribute :status. I tried to do this: class Task < …

Read More