What does inverse_of do? What SQL does it generate?
From the documentation, it seems like the :inverse_of
option is a method for avoiding SQL queries, not generating them. It's a hint to ActiveRecord to use already loaded data instead of fetching it again through a relationship.
Their example:
class Dungeon < ActiveRecord::Base
has_many :traps, :inverse_of => :dungeon
has_one :evil_wizard, :inverse_of => :dungeon
end
class Trap < ActiveRecord::Base
belongs_to :dungeon, :inverse_of => :traps
end
class EvilWizard < ActiveRecord::Base
belongs_to :dungeon, :inverse_of => :evil_wizard
end
In this case, calling dungeon.traps.first.dungeon
should return the original dungeon
object instead of loading a new one as would be the case by default.
I think :inverse_of
is most useful when you are working with associations that have not yet been persisted. E.g.:
class Project < ActiveRecord::Base
has_many :tasks, :inverse_of=>:project
end
class Task < ActiveRecord::Base
belongs_to :project, :inverse_of=>:tasks
end
Now, in the console:
irb> p = Project.new
=> #<Project id: nil, name: nil, ...>
irb> t = p.tasks.build
=> #<Task id: nil, project_id: nil, ...>
irb> t.project
=> #<Project id: nil, name: nil, ...>
Without the :inverse_of
arguments, t.project
would return nil
, because it triggers an sql query and the data isn't stored yet. With the :inverse_of
arguments, the data is retrieved from memory.