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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. |
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