Cached attributes in ActiveRecord

This gem allows to save specific attributes in cache and save it to DB after limited time.

classDevice < ActiveRecord::Baseattr_cached:lat,:lon,by: :last_activity,expires_in: 5.minutes# Override setter (always call _cached method version!)deflat=(s)ifsself.lat_cached=ssuper(s)endendend

This means that parameters lat, lon, last_activity are persisted in Rails.cache. When the Device record is loaded from DB, those parameters are loaded from cache (if last_activity in DB is lower than last_activity in cache)... If you call save on user record and only lat, lon and last_activity parameters were changed, the record will be stored in DB only if last_activity stored in DB are older than 5 minutes!

Known issues with older ActiveRecords

There is a problem in dirty checking currently open in Rails! rails/rails#21442 Please see the dont reset dirty model after not save test to avoid current issue. We hope it will be fixed in new version of rails.

Cache control

If you want to store your model data in other specified cache, you can override attr_cached_key method in your model.

classDeviceattr_cached:lat,:londefattr_cached_key"device_#{id}"endend

Behaviour

2.1.5 :010 > d = Device.find 1
Device Load (2.2ms) SELECT "devices".* FROM "devices" ORDER BY "devices"."id" DESC LIMIT 1
=> #<Device id: 1, user_id: 548, lat: nil, lng: nil, last_activity: nil, created_at: "2015-09-25 14:24:45", updated_at: "2015-09-28 15:40:25">
2.1.5 :012 > d.lng = 10.302
=> 10.302
2.1.5 :013 > d.last_activity = Time.zone.now
=> Mon, 28 Sep 2015 21:01:06 CEST +02:00
2.1.5 :014 > d.save! # This will touch the DB!
(0.3ms) BEGIN
SQL (3.4ms) UPDATE "devices"SET"last_activity" = $1, "lng" = $2, "updated_at" = $4 WHERE "devices"."id" = 1 [["last_activity", "2015-09-28 19:01:06.955555"], ["lng", 10.203], ["updated_at", "2015-09-28 19:02:40.173626"]]
(0.5ms) COMMIT
=> true
2.1.5 :015 > d = Device.find 1
Device Load (2.2ms) SELECT "devices".* FROM "devices" ORDER BY "devices"."id" DESC LIMIT 1
=> #<Device id: 1, user_id: 548, lat: nil, lng: 10.2013, last_activity: "2015-09-28 19:01:06.955555", created_at: "2015-09-25 14:24:45", updated_at: "2015-09-28 19:02:40.173626">
2.1.5 :016 > d.lat = 15.203
=> 15.203
2.1.5 :017 > d.last_activity = Time.zone.now.advance(seconds: 5)
=> Mon, 28 Sep 2015 21:04:42 CEST +02:00
2.1.5 :017 > d.save! # This will not!
(0.3ms) BEGIN
(0.2ms) COMMIT
=> true
2.1.5 :015 > d = Device.find 1
Device Load (2.2ms) SELECT "devices".* FROM "devices" ORDER BY "devices"."id" DESC LIMIT 1
=> #<Device id: 1, user_id: 548, lat: nil, lng: 10.2013, last_activity: "2015-09-28 19:01:06.955555", created_at: "2015-09-25 14:24:45", updated_at: "2015-09-28 19:02:40.173626">
2.1.5 :016 > d.lat
=> 15.203
2.1.5 :017 > d.lat = 12.203
=> 12.203
2.1.5 :018 > d.last_activity = Time.zone.now.advance(minutes: 10)
=> Mon, 28 Sep 2015 21:14:42 CEST +02:00
2.1.5 :020 > d.save! # This will
(0.3ms) BEGIN
SQL (3.4ms) UPDATE "devices"SET"last_activity" = $1, "lng" = $2, "updated_at" = $4 WHERE "devices"."id" = 1 [["last_activity", "2015-09-28 19:14:42.952355"], ["lng", 12.203], ["updated_at", "2015-09-28 19:10:20.174329"]]
(0.5ms) COMMIT
=> true

Force save

If you really want from some reason write record to database and you've changed only cached values, set cache_force_save on object to true.

device=Device.firstdevice.lat=5device.cache_force_save=truedevice.save!# This will update records in database (and each next saveonthisobjecttoo!)

Instalation

gem'attr_cached',github: 'netbrick/attr_cached'