UnknownAttributeError csv [英] UnknownAttributeError csv

问题描述

试图将csv记录上传到City模型数据库中，但出现错误

trying to upload csv record into City model database, getting error

ActiveRecord::UnknownAttributeError in PagesController#import

unknown attribute 'country ' for City.  (City.create! row.to_hash)

csv:

name     country    general_info1    general_info2 (etc)
Toronto  Canada     This is a test   (nil)

上传视图

<%= form_tag upload_path, multipart: true do %>
  <%= file_field_tag :file %>
  <%= submit_tag "import" %>
<% end %>

路线:

post '/upload' => 'pages#import'

PagesController

PagesController

def import
    City.import(params[:file])
end

城市模型

def self.import(file)
    logger.info "__________________"
    logger.info file.inspect
    logger.info file.path
    logger.info "__________________"

    CSV.foreach(file.path, headers: true) do |row|
      City.create! row.to_hash
      #puts '&&&&&&&&&&&&&&&&&&&&&&&' + row[1]
      logger.info row.inspect
    end

模式

ActiveRecord::Schema.define(version: 20160513090837) do

  create_table "cities", force: :cascade do |t|
    t.string   "name"
    t.string   "country"
    t.string   "general_info1"
    t.string   "general_info2"
    t.integer  "happiness_rating"
    t.integer  "family_safety_rating"
    t.string   "family_safety_info"
    t.integer  "bike_hobby_rating"
    t.string   "bike_hobby_info"
    t.integer  "accountant_rating"
    t.integer  "accountant_shortage_rating"
    t.string   "accountant_shortage"
    t.integer  "accountant_avg_salary"
    t.integer  "graphic_designer_rating"
    t.string   "graphic_designer_shortage"
    t.integer  "graphic_designer_avg_salary"
    t.integer  "journalist_rating"
    t.string   "journalist_shortage"
    t.integer  "journalist_avg_salary"
    t.datetime "created_at",                  null: false
    t.datetime "updated_at",                  null: false
  end

end

非常感谢

answer:

CSV.foreach(file.path, {headers: true, header_converters: :symbol}) do |row|
        City.create!(row.to_hash)
      end

推荐答案

首先，如果City模型的create!方法预期出现在cities表中的field不存在，则出现ActiveRecord::UnknownAttributeError .确保它在那里.

First of, ActiveRecord::UnknownAttributeError occurs if the field that City models's create! method is expecting to be present in cities table is absent. Make sure its there.

有人可以解释为什么标头必须是符号吗?

can somebody please explain why the header needs to be a symbol?

在红宝石中解析CSV时，通常会以Hash es的集合形式获取数据.在以下示例中，您可能已经注意到，所有Hash的keys都在重复，并且它们都是String数据.在Ruby中，每个String实例都占用单独的内存空间.

When you parse CSV in ruby, you normally get the data as collection of Hashes. In the following example you might have noticed that the keys to all the Hashes are repeating and they are String data. In Ruby every String instance occupies separate memory space.

csv.to_a.map {|row| row.to_hash }
# => [{"Year"=>"1997", "Make"=>"Ford", "Model"=>"E350", "Description"=>"ac, abs, moon", "Price"=>"3000.00"}, {"Year"=>"1999", "Make"=>"Chevy", "Model"=>"Venture \"Extended Edition\"", "Description"=>"", "Price"=>"4900.00"}, {"Year"=>"1999", "Make"=>"Chevy", "Model"=>"Venture \"Extended Edition, Very Large\"", "Description"=>nil, "Price"=>"5000.00"}, {"Year"=>"1996", "Make"=>"Jeep", "Model"=>"Grand Cherokee", "Description"=>"MUST SELL!\nair, moon roof, loaded", "Price"=>"4799.00"}]

说字符串computer占用8 bytes.如果我定义此字符串1000,000次，它将占用我RAM的8MB.

Say string computer occupies 8 bytes. if I define this string 1000,000 times, it will occupy 8MB of my RAM.

现在，如果您使用header_converters: :symbol，它将调用to_sym方法，该方法现在将keys定义为symbol s.

Now if you use header_converters: :symbol, this will invoke to_sym method which will now define the keys as symbols.

csv = CSV.new(body, :headers => true, :header_converters => :symbol)
csv.to_a.map {|row| row.to_hash }
# => [{:year=>"1997", :make=>"Ford", :model=>"E350", :description=>"ac, abs, moon", :price=>"3000.00"}, {:year=>"1999", :make=>"Chevy", :model=>"Venture \"Extended Edition\"", :description=>"", :price=>"4900.00"}, {:year=>"1999", :make=>"Chevy", :model=>"Venture \"Extended Edition, Very Large\"", :description=>nil, :price=>"5000.00"}, {:year=>"1996", :make=>"Jeep", :model=>"Grand Cherokee", :description=>"MUST SELL!\nair, moon roof, loaded", :price=>"4799.00"}]

符号有何特色?

符号可提高内存效率，并且检索速度非常快.如果您定义符号:computer 1000,000次，它将仅占用8Bytes内存.

Symbol is memory efficient and retrieval is very fast. if you define symbol :computer 1000,000 times it will only occupy 8Bytes of memory.

此说明如何解决我的问题?

您的CSV文件可能有成千上万行数据要转换为Hash.因此，要使此过程更快且内存效率更高，请使用header_converters: :symbol

You CSV file might have thousands of lines of data to be converted to Hash. So to make this process faster and memory efficient, you use header_converters: :symbol

有关更多信息，请参见此内容. http://ruby-doc.org/stdlib-2.0.0/libdoc/csv/rdoc/CSV.html#HeaderConverters

See this for more info http://ruby-doc.org/stdlib-2.0.0/libdoc/csv/rdoc/CSV.html#HeaderConverters

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