在 DataMapper 中有 n 个字符串答案

【问题标题】：has n of Strings in DataMapper在 DataMapper 中有 n 个字符串
【发布时间】：2012-12-08 09:40:35
【问题描述】：

我正在为 Web 服务编写客户端，其模型的一部分是属于用户的字符串列表，其中包含用户之前使用的用户名。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 has 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？

我当前的代码：

class User
  include DataMapper::Resource

  # Some Properties here

  has n, :also_known_as, 'String'
end

这产生的错误是这样的：

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>

产生错误的文件是这样的：

# 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

【问题讨论】：

标签： ruby gem datamapper

【解决方案1】：

你为什么在这里使用'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

我不确定你想使用String 作为模型名称。

您很可能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

【讨论】：

我的目标是简单地将平台字符串模型用于列表。从我的角度来看，当我存储的只是一个字符串列表时，使用完全独立的模型似乎有点过头了，因此我试图让 DataMapper 将列表映射到 String 类。
您只能与DataMapper::Resource 类建立数据库关系。

【解决方案2】：

如果您希望能够通过 datamapper 1.x 查询 DSL 搜索旧用户名，您需要定义一个额外的模型。

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，您可以使用序列化的大对象。作为建议，您可以像这样使用来自dm-types 的DataMapper::Property::YAML：

class User
  include DataMapper::Resource

  # ...

  property :also_known_as, YAML
end

【讨论】：