Ruby中的哈希的特定值的访问方法 [英] Accessor methods for specific values of a hash in Ruby

问题描述

我正在为Ruby编写一个API包装器，用于 Omeka API。 API的一部分是在Omeka网站上创建一个表示项目的类。对API的GET请求返回一个JSON对象，我将其转换为哈希（见下文，因为它很长）。我使用递归开放结构宝石，而不是让用户浏览长字符串创建访问器方法。例如：

  class OmekaItem 
 
 attr_accessor：data 
 
 def initialize （hash）
 @data = RecursiveOpenStruct.new（hash，：recurse_over_arrays => true）
 end 
 
 end 
  pre> 
 
 
假设我创建了一个 item 类的实例，让用户访问数据： item.data.id 或 item.data.modified 。
 
 
 
最重要的数据在元素texts数组中。有两种元素文本：Dublin Core和Item Type Metadata。我想为这些字段中的数据创建一个单独的Open Struct。这是我如何做的：
  class OmekaItem 
 
 attr_accessor：data，：dublin_core，：item_type_metadata 
 
 def initialize（hash）
 @data = RecursiveOpenStruct.new（hash，：recurse_over_arrays => true）
 
 dublin_core = Hash.new 
 item_type_metadata = Hash.new 
 @ data.element_texts.each do | element_text | 
 if element_text.element_set.name ==Dublin Core
 method_name = element_text.element.name.downcase.gsub（/ \s /，'_'）
 value = element_text。 text 
 dublin_core [method_name] = value 
 elsif element_text.element_set.name ==Item Type Metadata
 method_name = element_text.element.name.downcase.gsub（/ \s /， '_'）
 value = element_text.text 
 item_type_metadata [method_name] = value 
 end 
 end 
 
 @dublin_core = RecursiveOpenStruct.new（dublin_core） 
 @item_type_metadata = RecursiveOpenStruct.new（item_type_metadata）
 
 end 
 
 end 
  
现在用户可以通过类似这样的方法调用访问Dublin Core元数据： item.dublin_core.title 。 
 
 
 
到目前为止很好，但这是我被困住的地方。类需要实现一个 to_h 方法返回一个带有更改数据的原始格式的哈希值，以便我可以将其传递给POST和PUT方法。如果有人要通过调用 item.data.element_text [1] .text =My new data来更改数据，那么我可以很容易地调用open返回一个散列。但是如果用户更改 item.dublin_core.title =我的新标题，该数据将与存储在 @data 。如何让数据存储的两个地方排队？ 
 
 
 
 
 
 
项目的典型哈希值如下所示：
 >> pp hash 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/items/1，
 public=> true，
featured=> false，
added=>2013-07-13T04：47：08 + 00：00，
 modified=>2013-07-14T19：37：45 + 00：00，
item_type=> 
 {id=> 10，
url=>http：//localhost/omeka-2.1-rc1/api/item_types/10，
name =>Lesson Plan，
resource=>item_types}，
collection=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/collections/1，
resource =>collections}，
owner=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/users/1，
resource =>users}，
files=> 
 {count=> 0，
url=>http：//localhost/omeka-2.1-rc1/api/files？item = 1，
 resource=>files}，
tags=> []，
element_texts=> 
 [{html=> false，
text=>Item Title，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 50，
url=>http：//localhost/omeka-2.1-rc1/api/elements/50，
name ="Title，
resource=>elements}}，
 {html=> false，
text=& ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 49，
url=>http：//localhost/omeka-2.1-rc1/api/elements/49，
name =>主题，
resource=>元素}}，
 {html=> ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 37，
url=>http：//localhost/omeka-2.1-rc1/api/elements/37，
name =>Contributor，
resource=>elements}}，
 {html=> true，
text=& ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 41，
url=>http：//localhost/omeka-2.1-rc1/api/elements/41，
name ="Description，
resource=>elements}}，
 {html=> true，
text=& ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 39，
url=>http：//localhost/omeka-2.1-rc1/api/elements/39，
name =>创建者，
resource=>元素}}，
 {html=> false，
text=& ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 48，
url=>http：//localhost/omeka-2.1-rc1/api/elements/48，
name =>Source，
resource=>elements}}，
 {html=> ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 45，
url=>http：//localhost/omeka-2.1-rc1/api/elements/45，
name ="Publisher，
resource=>elements}}，
 {html=> false，
text=& ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 40，
url=>http：//localhost/omeka-2.1-rc1/api/elements/40，
name =>Date，
resource=>元素}}，
 {html=> false，
 ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 47，
url=>http：//localhost/omeka-2.1-rc1/api/elements/47，
name =Rights，
resource=>elements}}，
 {html=> false，
text=& ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 46，
url=>http：//localhost/omeka-2.1-rc1/api/elements/46，
name =>关系，
资源=>元素}}，
 {html=> false，
 ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 42，
url=>http：//localhost/omeka-2.1-rc1/api/elements/42，
name =>Format，
resource=>elements}}，
 {html=> false，
text=& ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 44，
url=>http：//localhost/omeka-2.1-rc1/api/elements/44，
name =>Language，
resource=>elements}}，
 {html=> false，
text=& ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 51，
url=>http：//localhost/omeka-2.1-rc1/api/elements/51，
name =>Type，
resource=>elements}}，
 {html=> false，
text=& ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 43，
url=>http：//localhost/omeka-2.1-rc1/api/elements/43，
name =>Identifier，
resource=>elements}}，
 {html=> false，
text=& ，
element_set=> 
 {id=> 1，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/1，
name =>Dublin Core，
resource=>element_sets}，
element=> 
 {id=> 38，
url=>http：//localhost/omeka-2.1-rc1/api/elements/38，
name =>Coverage，
resource=>elements}}，
 {html=> false，
text=> ，
element_set=> 
 {id=> 3，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/3，
name =>Item Type Metadata，
resource=>element_sets}，
element=& 
 {id=> 11，
url=>http：//localhost/omeka-2.1-rc1/api/elements/11，
name =>Duration，
resource=>elements}}，
 {html=> false，
text=> ，
element_set=> 
 {id=> 3，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/3，
name =>Item Type Metadata，
resource=>element_sets}，
element=> 
 {id=> 24，
url=>http：//localhost/omeka-2.1-rc1/api/elements/24，
name =>Standards，
resource=>elements}}，
 {html=> false，
text=> ，
element_set=> 
 {id=> 3，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/3，
 =>Item Type Metadata，
resource=>element_sets}，
element=> 
 {id=> 25，
url=>http：//localhost/omeka-2.1-rc1/api/elements/25，
name =>Objectives，
resource=>elements}}，
 {html=> false，
text=> ，
element_set=> 
 {id=> 3，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/3，
name =>Item Type Metadata，
resource=>element_sets}，
element=> 
 {id=> 26，
url=>http：//localhost/omeka-2.1-rc1/api/elements/26，
name =>Material，
resource=>elements}}，
 {html=> false，
text=>计划文本，
element_set=> 
 {id=> 3，
url=>http：//localhost/omeka-2.1-rc1/api/element_sets/3，
name =>Item Type Metadata，
resource=>element_sets}，
element=> 
 {id=> 27，
url=>http：//localhost/omeka-2.1-rc1/api/elements/27，
name =>Lesson Plan Text，
resource=>elements}}]，
extended_resources=> []} 
  
 
 
解决方案
这是我最后做的。它使用一些Ruby的元编程方法循环遍历元素文本，并为每个元素创建方法。两件事我不知道，真正帮助了这些。首先，使用 each_with_index 循环遍历数组，让我拥有数组中项的索引，这是创建访问器方法所必需的。第二，我学习了如何将一个值传递给proc;请参阅setter方法。
  class OmekaItem 
 
 attr_accessor：data 
 
 ＃将我们从API中获得的数据解析为方便的方法。来自API返回的JSON的所有数据
＃可作为RecursiveOpenStructs 
＃through @data。都柏林核心和项目类型元数据字段也是
＃可用，通过形式dc_title和itm_field的特殊方法。 
＃
＃@param hash [Hash]使用来自OmekaClient :: Client :: get_hash 
的哈希值
 def initialize（hash）
 @data = RecursiveOpenStruct。 new（hash，：recurse_over_arrays => true）
 
＃遍历元素文本，将它们分成Dublin Core和
＃项类型元数据元素。 e是元素文本散列; i是元素文本数组中element_text的
＃索引。 
 @ data.element_texts.each_with_index do | e，i | 
 if e.element_set.name ==Dublin Core
＃定义一个读取器方法，从这个元素中检索数据
＃text @data 
 self.class.send （：define_method，
＃方法的名称将是dc_title
 e.element.name.downcase.gsub（/ ^ /，'dc _'）。gsub（/ \ss /，'_'），
 proc {@ data.element_texts [i] .text} 
）
＃定义一个setter方法，用于设置
中此元素文本的数据＃@ data 
 self.class.send（：define_method，
＃方法的名称将采用dc_title =
 e.element.name.downcase.gsub（/ ^ /，'dc_'）。gsub（/ \s /，'_'）。gsub（/ $ /，'='），
 proc {| value | @ data.element_texts [i] value} 
）
 elsif e.element_set.name ==Item Type Metadata
＃定义一个读取器方法，从这个元素中检索数据
＃text in @data 
 self.class.send（：define_method，
＃方法的名称将具有形式itm_field
 e.element.name.downcase.gsub（/ ^ /，'itm_' ）.gsub（/ \s /，'_'），
 proc {@ data.element_texts [i] .text} 
）
＃定义一个setter方法，这个元素文本在
＃@ data 
 self.class.send（：define_method，
＃方法的名称将具有形式itm_title =
 e.element。 name.downcase.gsub（/ ^ /，'itm _'）。gsub（/ \s /，'_'）。gsub（/ $ /，'='），
 proc { @ data.element_texts [i] .text = value} 
）
 end 
 end 
 
 end 
 
 end 
  
 
I'm writing an API wrapper in Ruby for the Omeka API. Part of the API is making a class that represents an item on the Omeka site. A GET request to the API returns a JSON object, which I convert to a hash (see below, since it's long). Rather than making users navigate through a long hash, I'm using the Recursive Open Struct gem to create accessor methods. For example:
class OmekaItem

  attr_accessor :data

  def initialize(hash)
    @data = RecursiveOpenStruct.new(hash, :recurse_over_arrays => true)
  end

end
Assuming that I've made an instance of the class called item that lets the user access data like so: item.data.id or item.data.modified.

The most important data is in the element texts array. There are two kinds of element texts: "Dublin Core" and "Item Type Metadata." I'd like to create a separate Open Struct for the data in those fields. This is how I do that:
  class OmekaItem

    attr_accessor :data, :dublin_core, :item_type_metadata

    def initialize(hash)
      @data = RecursiveOpenStruct.new(hash, :recurse_over_arrays => true)

      dublin_core = Hash.new
      item_type_metadata = Hash.new
      @data.element_texts.each do |element_text|
        if element_text.element_set.name == "Dublin Core"
          method_name = element_text.element.name.downcase.gsub(/\s/, '_')
          value       = element_text.text
          dublin_core[method_name] = value
        elsif element_text.element_set.name == "Item Type Metadata"
          method_name = element_text.element.name.downcase.gsub(/\s/, '_')
          value       = element_text.text
          item_type_metadata[method_name] = value
        end
      end

      @dublin_core = RecursiveOpenStruct.new(dublin_core)
      @item_type_metadata = RecursiveOpenStruct.new(item_type_metadata)

    end

  end
Now users can access the Dublin Core metadata with method calls like this: item.dublin_core.title. 

So far so good, but this is where I'm stuck. The class needs to implement a to_h method to return a hash in the original format with changed data, so that I can pass it to POST and PUT methods. If someone were to change the data by calling item.data.element_text[1].text = "My new data" then I could easily call the method on the open struct that returns a hash. But if a user changes item.dublin_core.title = "My new title" that data will be separate from the open struct stored in @data. How can I go about making the two places where the data is stored line up? 



A typical hash for an item looks like this:
>> pp hash
{"id"=>1,
 "url"=>"http://localhost/omeka-2.1-rc1/api/items/1",
 "public"=>true,
 "featured"=>false,
 "added"=>"2013-07-13T04:47:08+00:00",
 "modified"=>"2013-07-14T19:37:45+00:00",
 "item_type"=>
  {"id"=>10,
   "url"=>"http://localhost/omeka-2.1-rc1/api/item_types/10",
   "name"=>"Lesson Plan",
   "resource"=>"item_types"},
 "collection"=>
  {"id"=>1,
   "url"=>"http://localhost/omeka-2.1-rc1/api/collections/1",
   "resource"=>"collections"},
 "owner"=>
  {"id"=>1,
   "url"=>"http://localhost/omeka-2.1-rc1/api/users/1",
   "resource"=>"users"},
 "files"=>
  {"count"=>0,
   "url"=>"http://localhost/omeka-2.1-rc1/api/files?item=1",
   "resource"=>"files"},
 "tags"=>[],
 "element_texts"=>
  [{"html"=>false,
    "text"=>"Item Title",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>50,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/50",
      "name"=>"Title",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Subject",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>49,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/49",
      "name"=>"Subject",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Contributor",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>37,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/37",
      "name"=>"Contributor",
      "resource"=>"elements"}},
   {"html"=>true,
    "text"=>"Item Description",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>41,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/41",
      "name"=>"Description",
      "resource"=>"elements"}},
   {"html"=>true,
    "text"=>"Item Creator",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>39,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/39",
      "name"=>"Creator",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Source",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>48,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/48",
      "name"=>"Source",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Publisher",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>45,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/45",
      "name"=>"Publisher",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Date",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>40,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/40",
      "name"=>"Date",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Rights",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>47,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/47",
      "name"=>"Rights",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Relation",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>46,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/46",
      "name"=>"Relation",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Format",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>42,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/42",
      "name"=>"Format",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Language",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>44,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/44",
      "name"=>"Language",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Type",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>51,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/51",
      "name"=>"Type",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Identifier",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>43,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/43",
      "name"=>"Identifier",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Coverage",
    "element_set"=>
     {"id"=>1,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/1",
      "name"=>"Dublin Core",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>38,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/38",
      "name"=>"Coverage",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Type Duration",
    "element_set"=>
     {"id"=>3,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/3",
      "name"=>"Item Type Metadata",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>11,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/11",
      "name"=>"Duration",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Type Standards",
    "element_set"=>
     {"id"=>3,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/3",
      "name"=>"Item Type Metadata",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>24,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/24",
      "name"=>"Standards",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Type Objectives",
    "element_set"=>
     {"id"=>3,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/3",
      "name"=>"Item Type Metadata",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>25,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/25",
      "name"=>"Objectives",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Type Materials",
    "element_set"=>
     {"id"=>3,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/3",
      "name"=>"Item Type Metadata",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>26,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/26",
      "name"=>"Materials",
      "resource"=>"elements"}},
   {"html"=>false,
    "text"=>"Item Type Lesson Plan Text",
    "element_set"=>
     {"id"=>3,
      "url"=>"http://localhost/omeka-2.1-rc1/api/element_sets/3",
      "name"=>"Item Type Metadata",
      "resource"=>"element_sets"},
    "element"=>
     {"id"=>27,
      "url"=>"http://localhost/omeka-2.1-rc1/api/elements/27",
      "name"=>"Lesson Plan Text",
      "resource"=>"elements"}}],
 "extended_resources"=>[]}

解决方案
This is what I ended up doing. It uses some of Ruby's metaprogramming methods to loop through the element texts, and create methods for each of them. The two things I didn't know that really helped out were these. First, looping through the array with each_with_index lets me have the index of the item in the array, which was necessary for creating the accessor methods. Second, I learned how to pass a value to a proc; see the setter methods.
  class OmekaItem

    attr_accessor :data

    # Parse the data we got from the API into handy methods. All of the data
    # from the JSON returned by the API is available as RecursiveOpenStructs
    # through @data. The Dublin Core and Item Type Metadata fields are also
    # available though special methods of the form dc_title and itm_field.
    #
    # @param  hash [Hash] Uses the hash from OmekaClient::Client::get_hash
    #
    def initialize(hash)
      @data = RecursiveOpenStruct.new(hash, :recurse_over_arrays => true)

      # Step through the element texts separating them into Dublin Core and
      # Item Type Metadata elements. e is the element text hash; i is the
      # index of the element_text in the array of element texts.
      @data.element_texts.each_with_index do |e, i|
        if e.element_set.name == "Dublin Core"
          # Define a reader method that retrieves the data from this element
          # text in @data
          self.class.send(:define_method,
            # The name of the method will have the form "dc_title"
            e.element.name.downcase.gsub(/^/, 'dc_').gsub(/\s/, '_'),
            proc{ @data.element_texts[i].text }
            )
          # Define a setter method that sets the data for this element text in
          # @ data
          self.class.send(:define_method,
            # The name of the method will have the form "dc_title="
            e.element.name.downcase.gsub(/^/, 'dc_').gsub(/\s/, '_').gsub(/$/, '='),
            proc{ |value| @data.element_texts[i].text = value }
            )
        elsif e.element_set.name == "Item Type Metadata"
          # Define a reader method that retrieves the data from this element
          # text in @data
          self.class.send(:define_method,
            # The name of the method will have the form "itm_field"
            e.element.name.downcase.gsub(/^/, 'itm_').gsub(/\s/, '_'),
            proc{ @data.element_texts[i].text }
            )
          # Define a setter method that sets the data for this element text in
          # @ data
          self.class.send(:define_method,
            # The name of the method will have the form "itm_title="
            e.element.name.downcase.gsub(/^/, 'itm_').gsub(/\s/, '_').gsub(/$/, '='),
            proc{ |value| @data.element_texts[i].text = value }
            )
        end
      end

    end

  end


                        
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