我将从rails 3 app迁移,它使用AR和arel到datamapper。我喜欢像Person.where(...)这样的范围链。其中(...)。somescope.paginate(...)。order(...)。如何从这种方法迁移到datamapper。
答案 0 :(得分:6)
DataMapper中的命名范围只是您在模型类上定义的类方法。在这些类方法中,您通常会使用某些条件调用#all
来获取DataMapper::Collection
。为了使您的类方法可链接,您必须确保返回DataMapper::Collection
。
为了完整起见,这里有安装说明......
gem install dm-core
gem install dm-migrations
gem install dm-sqlite-adapter
gem install dm-chunked_query
以及让你前进的代码(将其放入test.rb以获得最大的可重复性)
require 'rubygems'
require 'dm-core'
require 'dm-migrations'
require 'dm-chunked_query'
class Person
include DataMapper::Resource
property :id, Serial
property :name, String
property :hobby, String
property :country, String
property :continent, String
def self.european
all(:continent => 'Europe')
end
def self.hackers
all(:hobby => 'Hacking')
end
def self.named(name)
all(:name => name)
end
end
DataMapper::Logger.new($stdout, :debug)
DataMapper.setup(:default, 'sqlite::memory:')
DataMapper.finalize.auto_migrate!
1.upto(10) do |i|
Person.create(:name => "Alex", :hobby => 'Hacking', :country => "Country-#{i}", :continent => 'Europe')
end
# you could even skip the explicit call to #all
# i just left it in there because it reads nicely
Person.all.european.hackers.named('Alex').chunks(5).each_with_index do |chunk, idx|
puts "Rendering page #{idx + 1}"
chunk.each do |person|
puts "Someone named #{person.name} who lives in #{person.country}"
end
end
__END__
ruby-1.9.2-p180@datamapper mungo:dm-rails snusnu$ ruby test.rb
~ (0.000102) SELECT sqlite_version(*)
~ (0.000132) DROP TABLE IF EXISTS "people"
~ (0.000013) PRAGMA table_info("people")
~ (0.000315) CREATE TABLE "people" ("id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, "name" VARCHAR(50), "hobby" VARCHAR(50), "country" VARCHAR(50), "continent" VARCHAR(50))
~ (0.000049) INSERT INTO "people" ("name", "hobby", "country", "continent") VALUES ('Alex', 'Hacking', 'Country-1', 'Europe')
~ (0.000056) INSERT INTO "people" ("name", "hobby", "country", "continent") VALUES ('Alex', 'Hacking', 'Country-2', 'Europe')
~ (0.000044) INSERT INTO "people" ("name", "hobby", "country", "continent") VALUES ('Alex', 'Hacking', 'Country-3', 'Europe')
~ (0.000043) INSERT INTO "people" ("name", "hobby", "country", "continent") VALUES ('Alex', 'Hacking', 'Country-4', 'Europe')
~ (0.000037) INSERT INTO "people" ("name", "hobby", "country", "continent") VALUES ('Alex', 'Hacking', 'Country-5', 'Europe')
~ (0.000038) INSERT INTO "people" ("name", "hobby", "country", "continent") VALUES ('Alex', 'Hacking', 'Country-6', 'Europe')
~ (0.000035) INSERT INTO "people" ("name", "hobby", "country", "continent") VALUES ('Alex', 'Hacking', 'Country-7', 'Europe')
~ (0.000035) INSERT INTO "people" ("name", "hobby", "country", "continent") VALUES ('Alex', 'Hacking', 'Country-8', 'Europe')
~ (0.000036) INSERT INTO "people" ("name", "hobby", "country", "continent") VALUES ('Alex', 'Hacking', 'Country-9', 'Europe')
~ (0.000039) INSERT INTO "people" ("name", "hobby", "country", "continent") VALUES ('Alex', 'Hacking', 'Country-10', 'Europe')
~ (0.000069) SELECT "id", "name", "hobby", "country", "continent" FROM "people" WHERE ("continent" = 'Europe' AND "hobby" = 'Hacking' AND "name" = 'Alex') ORDER BY "id"
Rendering page 1
Someone named Alex who lives in Country-1
Someone named Alex who lives in Country-2
Someone named Alex who lives in Country-3
Someone named Alex who lives in Country-4
Someone named Alex who lives in Country-5
Rendering page 2
Someone named Alex who lives in Country-6
Someone named Alex who lives in Country-7
Someone named Alex who lives in Country-8
Someone named Alex who lives in Country-9
Someone named Alex who lives in Country-10
有关提供此示例中使用的#chunks
方法的低级分页方法(批处理)的详细信息,请参阅https://github.com/postmodern/dm-chunked_query。