ruby – 如何在MongoDB映射函数中对BSON对象进行字符串化？

我有包含字段xyz的文档

{ term: "puppies",page: { skip: 1,per_page: 20 } } // not useful as a composite key...
{ page: { skip: 1,per_page: 20 },term: "puppies" } // different order,same contents

为了确定xyz中的“顶部”值,我想将它们全部映射到类似的东西

emit('term="puppies",page={ skip: 1,per_page: 20 }',1); // composite key

但是我无法将嵌入的对象变成有意义的字符串：

emit('term="puppies",page=[object bson_object]',1); // not useful

有关使用函数而不是toString()的任何建议吗？

# return the top <num> values of <field> based on a query <selector>
#
# example: top(10,:xyz,{},{})
def top(num,field,selector,opts = {})
  m = ::BSON::Code.new <<-EOS
    function() {

      var keys = [];

      for (var key in this.#{field}) {
        keys.push(key);
      }

      keys.sort ();

      var sortedkeyvaluePairs = [];

      for (i in keys) {
        var key = keys[i];
        var value = this.#{field}[key];

        if (value.constructor.name == 'String') {
          var stringifiedValue = value;
        } else if (value.constructor.name == 'bson_object') {
          // this just says "[object bson_object]" which is not useful
          var stringifiedValue = value.toString();
        } else {
          var stringifiedValue = value.toString();
        }

        sortedkeyvaluePairs.push([key,stringifiedValue].join('='));
      }

      // hopefully we'll end up with something like
      // emit("term=puppies,page={skip:1,per_page:20}")
      // instead of
      // emit("term=puppies,page=[object bson_object]")
      emit(sortedkeyvaluePairs.join(','),1);
    }
  EOS
  r = ::BSON::Code.new <<-EOS
    function(k,vals) {
      var sum=0;
      for (var i in vals) sum += vals[i];
      return sum;
    }
  EOS
  docs = []
  collection.map_reduce(m,r,opts.merge(:query => selector)).find({},:limit => num,:sort => [['value',::Mongo::DESCENDING]]).each do |doc|
    docs.push doc
  end
  docs
end

解决方法

鉴于 MongoDB uses SpiderMonkey as its internal JS engine,你不能使用 JSON.stringify(即使/当MongoDB switches to V8时也能工作)或SpiderMonkey的非标准 toSource method？

(对不起,不能尝试ATM确认它的工作)