Question

我在我的rails应用程序中遇到此错误no block given (yield)，这是在我的文件elements = Element.where(study_version_id: self.id).find_each中引用此行我试图将某些数据导出到XML文件在我的应用程序中生成。当我尝试导出时，我有这个错误，我想帮助解决它。

整个代码相关：

def to_xml
    # Build the document and the header elements
    odm_document = Odm.new("ODM-#{self.id}", "Assero", "Tourmalet", Version::VERSION)
    odm = odm_document.root
    study = odm.add_study("S-#{self.id}")
    global_variables = study.add_global_variables()
    global_variables.add_study_name("#{self.name}")
    global_variables.add_study_description("#{self.description}")
    global_variables.add_protocol_name("#{self.protocol_name}")
    metadata_version = study.add_metadata_version("MDV-#{self.id}", "Metadata for #{self.description}", "Study export.")
    protocol = metadata_version.add_protocol()
    # Get the set of visits, forms and elements.
    visits = Visit.where(study_version_id: self.id).order(ordinal: :asc)
    forms = Form.where(study_version_id: self.id).order(ordinal: :asc)
    elements = Element.where(study_version_id: self.id).find_each
    # Build the Protocol element.
    visits.each do |visit|
      protocol.add_study_event_ref("SE-#{visit.ordinal}", "#{visit.ordinal}", "Yes", "")
    end
    # Build the StudyEventDef elements
    visits.each do |visit|
      study_event_def = metadata_version.add_study_event_def("SE-#{visit.ordinal}", "#{visit.long_name}", "No", "Scheduled", "")
      elements = Element.where(study_version_id: self.id, visit_id: visit.id).find_each
      elements.each do |element|
        #ConsoleLogger.log(C_CLASS_NAME, "to_xml", "Element=#{element.to_json}")
        form = Form.find(element.form_id)
        study_event_def.add_form_ref("#{form.form_id}", "#{form.ordinal}", "Yes", "")
      end
    end
    # Now the remainder of the metadata
    forms.each do |form|
      form_json = Mdr.form_to_hash(form.form_id, form.form_namespace)
      #ConsoleLogger.log(C_CLASS_NAME, "to_xml", "JSON=#{form_json}")
      xml_node(form_json, metadata_version, nil)
    end
    return odm_document.to_xml
  end

Answer 1

如果您使用的是elements，则无需将查询结果分配给本地变量find_each。而是使用块（do |element| ... end）

Element.where(study_version_id: self.id, visit_id: visit.id).find_each do |element|
  #ConsoleLogger.log(C_CLASS_NAME, "to_xml", "Element=#{element.to_json}")
  form = Form.find(element.form_id)
  study_event_def.add_form_ref("#{form.form_id}", "#{form.ordinal}", "Yes", "")
end

Answer 2

快速解决方案将find_each替换为all。如果您拥有小型数据库（我认为这是您的情况），它将起作用

find_each用于优化。它不会立即返回所有记录，而是返回记录集（默认为1000）。如果您有1.000.000记录，则会在尝试一次性加载时遇到our of memory异常。

您可以使用find_each用法重写代码：

Element.where(study_version_id: self.id, visit_id: visit.id).find_each do |elements|
  elements.each do |element|
    #ConsoleLogger.log(C_CLASS_NAME, "to_xml", "Element=#{element.to_json}")
    form = Form.find(element.form_id)
    study_event_def.add_form_ref("#{form.form_id}", "#{form.ordinal}", "Yes", "")
  end
end

但我90％肯定你应该选择：

elements = Element.where(study_version_id: self.id, visit_id: visit.id).all
elements.each do |element|
  #ConsoleLogger.log(C_CLASS_NAME, "to_xml", "Element=#{element.to_json}")
  form = Form.find(element.form_id)
  study_event_def.add_form_ref("#{form.form_id}", "#{form.ordinal}", "Yes", "")
end

Rails：没有给出块（yield）

2 个答案: