File: README — Documentation for cache

Intro

Cache-column aims to make it easy to store the return values of functoins in the database for recall later.

Examples

First add the following code to set-up the before_save filter and include the rest of the methods:

has_cached_columns

Next, we need to set-up the columns that hold our cached values. This is accomplished through a migration

script/generate cache_column OBJECT/TABLENAME feild:type

For example

script/generate cache_column listing high_price:float low_price:float number_of_price_points:integer

The above migration will add cache columns of the defined time to the listings table.

Now we need to add our cache column deffinations to the model.

The general format is

cache_column :column_name, options

So for our example we want to add

cache_column :high_price
cache_column :low_price
cache_column :number_of_price_points

Now this dosn’t do much so far other then map the virtual attribute

Object.high_price

to the database field

Ojbect.high_price_cache

No big deal, but the point is to store complex functions in the database. Lets say the high price attribute isn’t so strait forward, and is calculated in the find_high_price function

def find_high_price
  sleep(10)
  return '10.05'
end

We can now tell the gem to update the cached value every time the object is saved by changing the cache_column deffination to

cache_column :high_price, :on_save => :recheck, :action => :find_high_price

Its fairly self explanitory, but this just tells the gem to recheck the price stored in high_price_cache when the model is saved (or touched). The stored value is retreived from the function named in the :action key

There are a few other options like

cache_column :high_price, :on_save => :blank

and

cache_column :high_price, :on_save => :recheck, :action => :find_high_price, :update_validation => :high_price_changed

The :on_save => :blank just clears the value when it gets saved… not sure what the point of that is yet.

:update_validation should be set to the name of a function, if that function returns false then the cache column will not be updated.

I would love feedback, and bugs reports.

Limitations / Bugs

*Its my first gem.… so sorry for everything I’ve done wrong :) *It dosn’t store variables yet… Mabey next version. Till then use sanitize