Question

我正在为Web服务编写客户端，他们的部分模型是属于用户的字符串列表，其中包含用户经过的先前用户名。我正在尝试将DataMapper用于我的客户端gem，我的第一个想法是使用DataMapper的n语法，但我似乎无法将其应用于字符串。有没有更好的方法呢？

我目前的代码：

class User
  include DataMapper::Resource

  # Some Properties here

  has n, :also_known_as, 'String'
end

这产生的错误是：

irb(main):001:0> require 'cloudsdale'
NoMethodError: undefined method `relationships' for String:Class
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/associations/one_to_many.rb:109:in `finalize'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/model.rb:782:in `block in finalize_relationships'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/subject_set.rb:210:in `block in each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/ordered_set.rb:319:in `block in each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/ordered_set.rb:319:in `each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/ordered_set.rb:319:in `each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/subject_set.rb:210:in `each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/model.rb:782:in `finalize_relationships'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/model.rb:137:in `finalize'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core.rb:281:in `block in finalize'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/descendant_set.rb:64:in `block in each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/subject_set.rb:210:in `block in each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/ordered_set.rb:319:in `block in each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/ordered_set.rb:319:in `each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/ordered_set.rb:319:in `each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/subject_set.rb:210:in `each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/support/descendant_set.rb:63:in `each'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core.rb:281:in `finalize'
    from C:/Ruby193/lib/ruby/gems/1.9.1/gems/cloudsdale-0.0.1/lib/cloudsdale.rb:19:in `<top (required)>'
    from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:60:in `require'
    from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:60:in `rescue in require'
    from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:35:in `require'
    from (irb):1
    from C:/Ruby193/bin/irb:12:in `<main>'irb(main):002:0>

错误产生的文件是：

# Load in DataMapper
# Change the setup to meet your DB needs
require 'data_mapper'
DataMapper.setup(:default, 'abstract::')

# API objects
require 'cloudsdale/version'
require 'cloudsdale/api/api'
require 'cloudsdale/client'

# Models
require 'cloudsdale/models/user'
require 'cloudsdale/models/cloud'
require 'cloudsdale/models/avatar'
require 'cloudsdale/models/ban'
require 'cloudsdale/models/chat'

# Finalize DataMapper so the models Load
DataMapper.finalize

Answer 1

为什么在这里使用'String'？

has n, :also_known_as, 'String'

没有意义，删除它：

has n, :also_known_as

如果要设置模型，请使用:model选项：

has n, :also_known_as, :model => ModelName

并且我不确定您是否希望将String用作型号名称。

很可能你需要一个额外的模型来保留用户以前的名字：

class UserAlias
  include DataMapper::Resource

  # ...
end


class User
  include DataMapper::Resource

  # ...

  has n, :also_known_as, :model => UserAlias
end

Answer 2

如果您希望能够通过datamapper 1.x查询DSL搜索较旧的用户名，则需要定义其他模型。

class User
  include DataMapper::Resource

  # ...

  has n, :also_known_as, :model => UserNameHistory
end

class UsernameHistory
  include DataMapper::Resource
  property :id, Serial
  property :name
  belongs_to :user
end

如果您不需要通过旧用户名进行查询，则可以使用序列化的大对象。作为建议，您可以使用DataMapper::Property::YAML中的dm-types，如下所示：

class User
  include DataMapper::Resource

  # ...

  property :also_known_as, YAML
end

在DataMapper中有n个字符串

2 个答案: