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我需要创建一个包含以下表格的数据库：School、Address、Years、Types和Results。每个School只能有一个 Address和多个 Years，每个Year必须有多个 Types，并且每年每个Type只能有一个Results表。

我的 DataMapper 模型正在下降：

class School
  include DataMapper::Resource

  property :id, Serial
  property :title, String, :length => 225, :required => true
  property :type, String

  has n, :years
  has 1, :address
  has n, :types, :through => :years
  has n, :visits
end

class Year
  include DataMapper::Resource

  property :id, Serial
  property :year, Integer

  has n, :types
  has n, :schools

end

class Result
  include DataMapper::Resource

  property :id, Serial
  property :subject, String, :length => 225
  property :total, Integer
  property :range_1, Integer
  property :range_2, Integer
  property :range_3, Integer
  property :range_4, Integer
  property :range_5, Integer
  property :range_6, Integer
  property :range_7, Integer
  property :range_8, Integer
  property :range_9, Integer
  property :range_10, Integer

  belongs_to :type
end

class Type
  include DataMapper::Resource

  property :id, Serial
  property :name, String, :length => 225, :required => true

  has n, :results
  has n, :years
  has n, :schools, :through => :years
end

class Address
  include DataMapper::Resource

  property :id, Serial
  property :Village, String
  property :City, String
  property :District, String
  property :State, String

  belongs_to :school
end

我找不到更好的方法来声明表之间的关联。也许你可以提出更好的建议？

还有，如何选择取决于学校和年份的具体结果？

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