-
-
Save FND/1244491 to your computer and use it in GitHub Desktop.
Gemfile.lock |
#!/usr/bin/env ruby | |
# encoding: UTF-8 | |
# test case for eager loading of nested associations with DataMapper | |
require 'rubygems' | |
require 'dm-core' | |
require 'dm-constraints' | |
require 'dm-migrations' | |
require 'eager_loading' | |
DataMapper::Logger.new($stdout, :debug) | |
DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/db.sqlite") | |
class Person | |
include DataMapper::Resource | |
property :id, Serial | |
property :name, String, :required => true | |
has n, :vehicles | |
end | |
class Vehicle | |
include DataMapper::Resource | |
property :id, Serial | |
property :name, String, :required => true | |
has n, :components | |
end | |
class Component | |
include DataMapper::Resource | |
property :id, Serial | |
property :name, String, :required => true | |
belongs_to :manufacturer | |
end | |
class Manufacturer | |
include DataMapper::Resource | |
property :id, Serial | |
property :name, String, :required => true | |
end | |
DataMapper.auto_migrate! | |
# generate test data | |
Person.create(:name => "FND", :vehicles => [ | |
Vehicle.create(:name => "Taurus", :components => [ | |
Component.create(:name => "engine", | |
:manufacturer => Manufacturer.create(:name => "Ford")), | |
Component.create(:name => "radio", | |
:manufacturer => Manufacturer.create(:name => "Bose")) | |
]), | |
Vehicle.create(:name => "fixie", :components => [ | |
Component.create(:name => "frame", | |
:manufacturer => Manufacturer.create(:name => "Campagnolo")), | |
Component.create(:name => "breaks", | |
:manufacturer => Manufacturer.create(:name => "Shimano")) | |
]) | |
]) | |
Person.create(:name => "tillsc", :vehicles => [ | |
Vehicle.create(:name => "Golf", :components => [ | |
Component.create(:name => "engine", | |
:manufacturer => Manufacturer.create(:name => "VW")) | |
]) | |
]) | |
# retrieve data | |
puts "", "[INFO] test case A" | |
person = Person.get!(1) | |
puts person.vehicles.components.manufacturer.map(&:name).join(", ") | |
puts "", "[INFO] test case B" | |
people = Person.all | |
people.each do |person| | |
person.vehicles.each do |vehicle| | |
puts sprintf("%-10s %-10s", person.name, vehicle.name) | |
end | |
end | |
puts "", "[INFO] test case C ===== /!\ n+1 hazard ====" | |
people = Person.all | |
people.each do |person| | |
person.vehicles.each do |vehicle| | |
vehicle.components.each do |component| | |
puts sprintf("%-10s %-10s %-10s", person.name, vehicle.name, component.name) | |
end | |
end | |
end | |
puts "", "[INFO] test case D" | |
people = Person.all | |
people.eager_load(Person.vehicles.components).each do |person| | |
person.vehicles.each do |vehicle| | |
vehicle.components.each do |component| | |
puts sprintf("%-10s %-10s %-10s", person.name, vehicle.name, component.name) | |
end | |
end | |
end |
# manual eager loading for DataMapper | |
# adapted from Chris Corbyn: https://gist.github.com/1244491#gistcomment-56797 | |
module EagerLoading | |
def eager_load(query_path) | |
scope = self | |
query_path.relationships.each do |relation| | |
source_key = relation.source_key.first # TODO: rename | |
target_key = relation.target_key.first # TODO: rename | |
# for each level in the query path, collect all the resources referencing | |
# keys at the current scope | |
next_scope = relation.target_model.all(target_key.name => scope. | |
collect(&:"#{source_key.name}")) | |
# map target keys to the resources that exist for them | |
links = next_scope.inject({}) do |map, resource| | |
map.merge(target_key.get(resource) => [resource]) { |k, v1, v2| v1 + v2 } | |
end | |
# now pre-load those from the map | |
scope.each do |parent| | |
if links.key?(source_key.get(parent)) | |
parent.instance_variable_set(:"@#{relation.name}", | |
links[source_key.get(parent)]) | |
end | |
end | |
# and step into the next nesting level | |
scope = next_scope | |
end | |
self | |
end | |
end | |
DataMapper::Collection.send(:include, EagerLoading) |
source :rubygems | |
DM_VERSION = '~> 1.2.0.rc2' | |
gem 'dm-core', DM_VERSION | |
gem 'dm-constraints', DM_VERSION | |
gem 'dm-migrations', DM_VERSION | |
gem 'dm-sqlite-adapter', DM_VERSION |
#!/usr/bin/env sh | |
rm db.sqlite | |
# reformat SQL queries for readability | |
bundle exec ./dm_el.rb | perl -pe 's#SELECT .*? (FROM ".*?" )(.*)#\1SELECT ... \2#' |
Awesome advice in Relationship#set
! Will try that. Classic example of getting a bit lost :P (Excuse the fragmented response... I'm a bit distracted with food and another coding problem simultaneously ;))
Hmm, I was just looking through some of Relationship
, and I noticed #eager_load
, which looks like exactly the API for this situation. So if I'm reading it correctly, you could simplify the whole thing to:
def load(query_path)
query_path.relationships.inject(@collection) do |scope, relationship|
relationship.eager_load(scope)
end
end
(BTW, I've vacillated, and I now prefer passing the Query::Path
to #load
instead of #initialize
(reverting to how you had it before). It seems more coherent, even though EagerLoader is probably still a single-use object.)
It's too late here for me to start hacking on this right now, but I'm going to try to make time to poke at it tomorrow.
@d11wtq—looks like Relationship#eager_load
does work; check out my fork of this gist: https://gist.github.com/1297105
Hey guys, I know this is an old thread, but check this out: https://gist.github.com/3100034
Re: relationship as a predicate, I tried something (I forget what) and while it didn't error, it didn't produce the correct results. I almost certainly did the wrong thing though. Are you able to check out the original gist, drop in my code then see if you get the correct output with your suggested simplification?
You should see the following under the "test case C" heading:
I always get a bit lost poking around in dm-core, but I always learn something new. It would be good to clear that "FIXME" :)