Chrome, Safari and Firefox serialize Date objects to strings such
as 'Mon May 28 2012 00:00:00 GMT-0700 (PDT)'. When these strings
are parsed the zone is interpreted as 'GMT-0700' which doesn't
exist in the TzInfo list of timezones.
By taking advantage of the improved date/time handling in 1.9.3
we can use `Date._parse` and the `:offset` value which is parsed
correctly.
Three tests were amended to make them pass:
1. test_parse_with_old_date
This needed changing to a different value because the original
value was before EST was adopted so was being changed to a
LMT (Local Mean Time) value after the change. It didn't before
because `DateTime` just has offsets from UTC not timezones.
2. test_parse_should_not_black_out_system_timezone_dst_jump
Changed the implementation of this test as the stubs were
dependent on internal implementation details of the test.
Confirmed that the modified test still failed when the
implementation of `parse` was restored to pre-#5571.
3. test_parse_should_black_out_app_timezone_dst_jump
Ditto.
Closes#5770.
At present, ActiveRecord::Delegation compiles delegation methods on a
global basis. The compiled methods apply to all subsequent Relation
instances. This creates several problems:
1) After Post.all.recent has been called, User.all.respond_to?(:recent)
will be true, even if User.all.recent will actually raise an error due
to no User.recent method existing. (See #8080.)
2) Depending on the AR class, the delegation should do different things.
For example, if a Post.zip method exists, then Post.all.zip should call
it. But this will then result in User.zip being called by a subsequent
User.all.zip, even if User.zip does not exist, when in fact
User.all.zip should call User.all.to_a.zip. (There are various
variants of this problem.)
We are creating these compiled delegations in order to avoid method
missing and to avoid repeating logic on each invocation.
One way of handling these issues is to add additional checks in various
places to ensure we're doing the "right thing". However, this makes the
compiled methods signficantly slower. In which case, there's almost no
point in avoiding method_missing at all. (See #8127 for a proposed
solution which takes this approach.)
This is an alternative approach which involves creating a subclass of
ActiveRecord::Relation for each AR class represented. So, with this
patch, Post.all.class != User.all.class. This means that the delegations
are compiled for and only apply to a single AR class. A compiled method
for Post.all will not be invoked from User.all.
This solves the above issues without incurring significant performance
penalties. It's designed to be relatively seamless, however the downside
is a bit of complexity and potentially confusion for a user who thinks
that Post.all and User.all should be instances of the same class.
Benchmark
---------
require 'active_record'
require 'benchmark/ips'
class Post < ActiveRecord::Base
establish_connection adapter: 'sqlite3', database: ':memory:'
connection.create_table :posts
def self.omg
:omg
end
end
relation = Post.all
Benchmark.ips do |r|
r.report('delegation') { relation.omg }
r.report('constructing') { Post.all }
end
Before
------
Calculating -------------------------------------
delegation 4392 i/100ms
constructing 4780 i/100ms
-------------------------------------------------
delegation 144235.9 (±27.7%) i/s - 663192 in 5.038075s
constructing 182015.5 (±21.2%) i/s - 850840 in 5.005364s
After
-----
Calculating -------------------------------------
delegation 6677 i/100ms
constructing 6260 i/100ms
-------------------------------------------------
delegation 166828.2 (±34.2%) i/s - 754501 in 5.001430s
constructing 116575.5 (±18.6%) i/s - 563400 in 5.036690s
Comments
--------
Bear in mind that the standard deviations in the above are huge, so we
can't compare the numbers too directly. However, we can conclude that
Relation construction has become a little slower (as we'd expect), but
not by a huge huge amount, and we can still construct a large number of
Relations quite quickly.
Keying these hashes by klass causes reloadable classes to never get
freed. Thanks to @thedarkone for pointing this out in
the comments on 221571beb6b4bb7437989bdefaf421f993ab6002.
This doesn't seem to make a massive difference to performance.
Benchmark
---------
require 'active_record'
require 'benchmark/ips'
class Post < ActiveRecord::Base
establish_connection adapter: 'sqlite3', database: ':memory:'
end
GC.disable
Benchmark.ips(20) do |r|
r.report { Post.connection }
end
Before
------
Calculating -------------------------------------
5632 i/100ms
-------------------------------------------------
218671.0 (±1.9%) i/s - 4364800 in 19.969401s
After
-----
Calculating -------------------------------------
8743 i/100ms
-------------------------------------------------
206525.9 (±17.8%) i/s - 4039266 in 19.992590s
Two big features that are only barely related in the same guide. Seems
bad.
I did not check references to these guides yet, so some links may need
to be updated.
Some guides work without 'the'. For instance, 'Migrations' or
'Form Helpers.' But when we talk about the asset pipeline, we...
always say 'the asset pipeline.' The guide title should reflect this.
