我如何与Rails / ActiveRecord创建多态的has_and_belongs_to_many关系?
我看到的大多数示例都涉及创建belongs_to关系,该关系将我的多态性限制为仅与一个父级相关:
表:任务
表:Tasks_Targets
表:CustomerStore
表:SoftwareSystem
在这种情况下,CustomerStore和SoftwareSystem都属于“Targetable”类型。据我所知,如果我实现大多数示例所显示的多态关系,我只能将Targetable与任务关联。
一些澄清可能有所帮助,因为大多数在线搜索仍然留下这种关系背后的一些理论无法解释......
谢谢!
答案 0 :(得分:6)
鉴于您对域名的解释,我已经提出了一个小型的测试驱动示例,说明如何解决您的问题。如果您发现任何域名不一致,请随时进一步澄清(我正在使用我的acts_as_fu gem
动态启动测试模型)。
require 'acts_as_fu'
# class Task < ActiveRecord::Base
build_model(:tasks) do
integer :task_target_id
has_many :task_targets
has_many :customer_stores, :through => :task_targets, :source => :targetable, :source_type => 'CustomerStore'
has_many :software_systems, :through => :task_targets, :source => :targetable, :source_type => 'SoftwareSystem'
end
# class TaskTarget < ActiveRecord::Base
build_model(:task_targets) do
string :targetable_type
integer :targetable_id
integer :task_id
belongs_to :targetable, :polymorphic => true
belongs_to :task
end
# class CustomerStore < ActiveRecord::Base
build_model(:customer_stores) do
has_many :task_targets, :as => :targetable
has_many :tasks, :through => :task_targets
end
# class SoftwareSystem < ActiveRecord::Base
build_model(:software_systems) do
has_many :task_targets, :as => :targetable
has_many :tasks, :through => :task_targets
end
require 'test/unit'
class PolymorphicDomainTest < Test::Unit::TestCase
# Test that customer stores can have multiple tasks
def test_customer_store_gets_task
task = Task.create!
customer_store = CustomerStore.create!
customer_store.task_targets.create! :task => task
assert customer_store.tasks.include?(task)
end
def test_many_customer_stores_get_task
task_a = Task.create!
task_b = Task.create!
customer_store = CustomerStore.create! :tasks => [task_a, task_b]
assert customer_store.tasks.include?(task_a)
assert customer_store.tasks.include?(task_b)
end
# Test that software systems can have multiple tasks
def test_software_system_gets_task
task = Task.create!
software_system = SoftwareSystem.create!
software_system.task_targets.create! :task => task
assert software_system.tasks.include?(task)
end
def test_many_software_systems_get_task
task_a = Task.create!
task_b = Task.create!
software_system = SoftwareSystem.create! :tasks => [task_a, task_b]
assert software_system.tasks.include?(task_a)
assert software_system.tasks.include?(task_b)
end
# Test that Tasks can have multiple customer stores
def test_task_has_many_customer_stores
task = Task.create!
customer_store_a = CustomerStore.create!
customer_store_b = CustomerStore.create!
task.customer_stores = [customer_store_a, customer_store_b]
task.save!
task.reload
assert task.customer_stores.include?(customer_store_a)
assert task.customer_stores.include?(customer_store_b)
end
# Test that Tasks can have multiple software systems
def test_task_has_many_software_systems
task = Task.create!
software_system_a = SoftwareSystem.create!
software_system_b = SoftwareSystem.create!
task.software_systems = [software_system_a, software_system_b]
task.save!
task.reload
assert task.software_systems.include?(software_system_a)
assert task.software_systems.include?(software_system_b)
end
end
答案 1 :(得分:-1)
为了补充nakajima关于你的关注的答案,我会这样做:
class Task < ActiveRecord::Base
def targets
# Get Array of all targetables
tt = TaskTarget.select_all("SELECT targetable_type, targetable_id FROM task_targerts WHERE task_id = #{self[:id]}")
# Build Hash of targetable_type => Array of targetable_ids
targetables = Hash.new { |hash, key| hash[key] = [] }
tt.each do |targetable|
targetables[targetable.targetable_type] << targetable.targetable_id
end
# Query each "targetable" table once and merge all results
targetables.keys.map{|key| (eval key).find(targetables[key])}.flatten
end
end
确保在表task_id
中对task_targets
编制索引。