ruby - DataMapper 中的关联

Question

我在以下代码中遇到关联问题。

我遇到的错误是对最后一行代码的评论。

编辑:我简化了代码...

require 'rubygems'
require 'data_mapper' # requires all the gems listed above
require 'pp'

DataMapper.setup(:default, 'sqlite:///Users/chris/Dropbox/HawkEye-DB Test/store.sqlite')

class Manufacturer
  include DataMapper::Resource
  property :id, Serial
  property :name, String

  has n, :products
end

class Product
  include DataMapper::Resource
  property :id, Serial    
  property :name, String

  belongs_to :manufacturer
  has 1, :productoptionset
end


class Productoptionset
  include DataMapper::Resource
  property :id, Serial    
  property :name, String

  belongs_to :product

end

DataMapper.auto_migrate!



# Make some manufactureres
gortex = Manufacturer.create(:name => 'Gortex')
garmin = Manufacturer.create(:name => 'Garmin')

gps = garmin.products.create(:name => 'GPS Unit')

samegps = Product.get(1)

pp samegps.productoptionset.create # undefined method `create' for nil:NilClass (NoMethodError)

Answer 1

create 是一个类方法(有点像 Java 中的静态方法)所以它不能在实例(或本例中的非实例)上调用:)

你可以像这样创建你的对象

class Manufacturer
  include DataMapper::Resource
  property :id, Serial
  property :name, String

  has n, :products
end

class Product
  include DataMapper::Resource
  property :id, Serial    
  property :manufacturer_id, Integer
  property :name, String

  belongs_to :manufacturer
  has 1, :productoptionset
end


class Productoptionset
  include DataMapper::Resource
  property :id, Serial  
  property :product_id, Integer
  property :name, String

  belongs_to :product
end

DataMapper.auto_migrate!



# Make some manufactureres
gortex = Manufacturer.create(:name => 'Gortex')
garmin = Manufacturer.create(:name => 'Garmin')

garmin.products << Product.create(:name => 'GPS Unit')

samegps = Product.get(1)

samegps.productoptionset = Productoptionset.create(:name => "MyProductoptionset")