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Code Show and Tell: PolymorphicFinder
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class ApplicationController < ActionController::Base | |
private | |
def requested_purchaseable | |
PolymorphicFinder. | |
finding(Section, :id, [:section_id]). | |
finding(TeamPlan, :sku, [:team_plan_id]). | |
finding(IndividualPlan, :sku, [:individual_plan_id]). | |
finding(Product, :id, [:product_id, :screencast_id, :book_id, :show_id]). | |
find(params) | |
end | |
end |
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# Finds one of several possible polymorphic members from params based on a list | |
# of relations to look in and attributes to look for. | |
# | |
# Each polymorphic member will be tried in turn. If an ID is present that | |
# doesn't correspond to an existing row, or if none of the possible IDs are | |
# present in the params, an exception will be raised. | |
class PolymorphicFinder | |
def initialize(finder) | |
@finder = finder | |
end | |
def self.finding(*args) | |
new(NullFinder.new).finding(*args) | |
end | |
def finding(relation, attribute, param_names) | |
new_finder = param_names.inject(@finder) do |fallback, param_name| | |
Finder.new(relation, attribute, param_name, fallback) | |
end | |
self.class.new(new_finder) | |
end | |
def find(params) | |
@finder.find(params) | |
end | |
private | |
class Finder | |
def initialize(relation, attribute, param_name, fallback) | |
@relation = relation | |
@attribute = attribute | |
@param_name = param_name | |
@fallback = fallback | |
end | |
def find(params) | |
if id = params[@param_name] | |
@relation.where(@attribute => id).first! | |
else | |
@fallback.find(params) | |
end | |
end | |
end | |
class NullFinder | |
def find(params) | |
raise( | |
ActiveRecord::RecordNotFound, | |
"Can't find a polymorphic record without an ID: #{params.inspect}" | |
) | |
end | |
end | |
private_constant :Finder, :NullFinder | |
end |
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require 'spec_helper' | |
describe PolymorphicFinder do | |
describe '#find' do | |
it 'finds the first given finder when present' do | |
individual_plan = create(:individual_plan, sku: 'abc') | |
result = PolymorphicFinder. | |
finding(IndividualPlan, :sku, [:individual_plan_id]). | |
find(individual_plan_id: 'abc') | |
expect(result).to eq(individual_plan) | |
end | |
it 'finds the first of several possible params' do | |
screencast = create(:screencast) | |
result = PolymorphicFinder. | |
finding(Product, :id, [:book_id, :screencast_id, :product_id]). | |
find(screencast_id: screencast.to_param) | |
expect(result).to eq(screencast) | |
end | |
it 'cascades when the first finder is not present' do | |
create(:individual_plan, sku: 'abc') | |
team_plan = create(:team_plan, sku: 'def') | |
result = PolymorphicFinder. | |
finding(IndividualPlan, :sku, [:individual_plan_id]). | |
finding(TeamPlan, :sku, [:team_plan_id]). | |
find(team_plan_id: 'def') | |
expect(result).to eq(team_plan) | |
end | |
it 'raises an exception for an unknown ID' do | |
create(:individual_plan, sku: 'abc') | |
finder = PolymorphicFinder. | |
finding(IndividualPlan, :sku, [:individual_plan_id]) | |
expect { finder.find(individual_plan_id: 'def') }. | |
to raise_error(ActiveRecord::RecordNotFound) | |
end | |
it 'raises an exception without any ID' do | |
params = { 'key' => 'value' } | |
finder = PolymorphicFinder. | |
finding(IndividualPlan, :sku, [:individual_plan_id]) | |
expect { finder.find(params) }. | |
to raise_error(ActiveRecord::RecordNotFound, /#{Regexp.escape(params.inspect)}/) | |
end | |
end | |
end |
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@pithyless, I agree, the first example it took me awhile to understand what it was doing, it seemed like too much abstraction. However, your example I understood exactly what was going on in a matter of seconds.