【发布时间】：2012-11-29 10:58:43
【问题描述】：
我的应用程序有一个 Job 模型。系统中的每个作业都有一个contact。这就像如果您需要询问有关工作的问题，您会打电话给一个人。联系人可以是 client 或客户的员工 (ClientEmployee)。
class Job < ActiveRecord::Base
belongs_to :contact, polymorphic: true
end
class Client < ActiveRecord::Base
has_many :jobs, as: :contact
has_many :employees, class_name: 'ClientEmployee'
end
class ClientEmployee < ActiveRecord::Base
belongs_to :client
has_many :jobs, as: :contact
end
客户有commissioned_jobs 的想法。客户委托的工作是客户是联系人或客户的一名员工是联系人的工作。
class Client < ActiveRecord::Base
has_many :jobs, as: :contact
has_many :employee_jobs, through: :employees, source: :jobs
def commissioned_jobs
jobs << employee_jobs
end
end
旁白：这个方法有点小技巧，因为它返回一个数组而不是ActiveRecord::Relation。如果我尝试将工作连接到employee_jobs 中，它也会爆炸，这也很有趣。它可能会也可能不会满足我的目的。
我想为Client 添加一个名为with_commissioned_jobs 的范围。这应该返回系统中所有有工作或有工作的员工的客户。
class Client < ActiveRecord::Base
def self.with_commissioned_jobs
# I can get clients with jobs using: joins(:jobs). How do
# I also include clients with employees who have jobs?
end
end
如何实现这个方法？
我使用的是 Rails 3.2.9。
更新：
我已经取得了一些进展，现在我有两种方法，每种方法都可以完成我需要的一半。
class Client < ActiveRecord::Base
# Return all clients who have an employee with at least one job.
def self.with_employee_jobs
joins(employees: :jobs)
# SQL: SELECT "clients".* FROM "clients" INNER JOIN "client_employees" ON "client_employees"."employer_id" = "clients"."id" INNER JOIN "jobs" ON "jobs"."contact_id" = "client_employees"."id" AND "jobs"."contact_type" = 'ClientEmployee'
end
# Return all clients who have at least one job.
def self.with_jobs
joins(:jobs)
# SQL: SELECT "clients".* FROM "clients" INNER JOIN "jobs" ON "jobs"."contact_id" = "clients"."id" AND "jobs"."contact_type" = 'Client'
end
end
现在我需要做的就是将这两个方法调用合并为一个ActiveRecord::Relation。我显然可以这样做：
def self.with_commissioned_jobs
with_jobs + with_employee_jobs
end
问题是它返回一个数组而不是Relation 的实例，我无法在其上链接更多范围。
更新 2：
使用merge 似乎也不起作用。这是 AR 查询和生成的 SQL。
joins(:jobs).merge(joins(employees: :jobs))
SELECT "clients".* FROM "clients" INNER JOIN "jobs"
ON "jobs"."contact_id" = "clients"."id"
AND "jobs"."contact_type" = 'Client'
INNER JOIN "client_employees"
ON "client_employees"."employer_id" = "clients"."id"
INNER JOIN "jobs" "jobs_client_employees"
ON "jobs_client_employees"."contact_id" = "client_employees"."id"
AND "jobs_client_employees"."contact_type" = 'ClientEmployee'
顺便说一下，这是我想要通过的测试。第一次测试失败，因为我使用合并时结果为零。
describe "with_commissioned_jobs" do
# A client with a job.
let!(:client_with) { create :client }
let!(:job) { create :job, contact: client_with }
# A client who does not himself have a job, but who has an employee
# with a job.
let!(:client_with_emp) { create :client }
let!(:employee) { create :client_employee, employer: client_with_emp }
let!(:emp_job) { create :job, contact: employee }
# A client with nothing. Should not show up.
let!(:client_without) { create :client }
it "should return clients with jobs and clients with employee jobs" do
Client.with_commissioned_jobs.should == [client_with, client_with_emp]
end
it "should return a relation" do
Client.with_commissioned_jobs.should be_instance_of(ActiveRecord::Relation)
end
end
【问题讨论】：
-
你调查过arel吗？ github.com/rails/arel 它有一个或条件用于查询，并且可以很好地处理复杂的连接。
-
我当然也会接受基于 Arel 的解决方案。我花了好几个小时试图想出一个，但我似乎无法管理它。
标签： ruby-on-rails ruby-on-rails-3 activerecord ruby-on-rails-3.2