Rails caching model variables - how to "force reload"?

Question

I'm implementing a heap data structure in Rails, so I've got basically a binary tree, with nodes that have id, name, and parent_id.

I've noticed a really strange error when I try to "bubble up" one of my nodes. Here's what's up.

node = Item.find(266)
node.children.size
 => 0

node.swap_up
node.children.size
 => 0

node = Item.find(266)
node.children.size
 => 2

The behavior I'm expecting to see is that after I swap_up the node, it should have 2 children (as a result of bubbling up one level in the tree). But somehow the value of 0 "persists" until I "re-get" the node from ActiveRecord.

Here's the relevant definition from my model/item.rb

belongs_to :parent, :class_name => 'Item'
has_many :children, :class_name => 'Item', :foreign_key => 'parent_id'

This is causing all kinds of insane behavior in my heap implementation. Is there any way I can ensure that a node's children are "updated" when methods are called that affect it? (Or that more accurately, that affect the parent_id of other nodes to start pointing to it?)

Any help you guys might have would be invaluable. Thanks!

Answer 1

Here is a suggestion that may help.

This retrives item from db

node = Item.find(266)
node.children.size
 => 0

This uses cached item

node.swap_up
node.children.size
 => 0

I believe you can get rid of the cached copy and force it to go back to the db by doing this

node.swap_up
node.children(true).size
 # should get => 2

instead of having to query the db again.