Why does the "save" return true, but database has a void record?

Question

I have written a Rails app that communities with front end by json-rpc. The ActiveRecord Class is:

class ProcessingDocument < ActiveRecord::Base
  attr_accessible :command, :comment, :creator, :emergency_level, :file_name, :is_locked, :is_removed, :last_status, :next_status, :owner_id, :paper_title, :receiver, :sender, :status, :suggest, :unit_id, :uuid, :workflow_id
  attr_accessor :command, :comment, :creator, :emergency_level, :file_name, :is_locked, :is_removed, :last_status, :next_status, :owner_id, :paper_title, :receiver, :sender, :status, :suggest, :unit_id, :uuid, :workflow_id

  def self.all_propertoes
    [:command, :comment, :creator, :emergency_level, :file_name, :is_locked, :is_removed, :last_status, :next_status, :owner_id, :paper_title, :receiver, :sender, :status, :suggest, :unit_id, :uuid, :workflow_id]
  end
end

And the Controller dynamic updates the object of ProcessingDocument by json.

def pd_create(json)
    pd_now = ProcessingDocument.new(:uuid => generate_uuid)
    json["params"].each do |k, v|   # the json["params"] is a Hash
        if ProcessingDocument.all_propertoes.include? k.to_sym
            pd_now.send("#{k}=", v)
        else
            render json: default_fail_json(json, __method__)
            return
        end
    end

    if pd_now.save
        debug_method pd_now.to_json  # this is a stdout bebug

        result = { :uuid => pd_now.uuid }
        render json: respond_data(json, result, nil)
    else
        render json: default_fail_json(json, __method__)
    end
end

When I post a json {"status":"1", "command":"stuff"}, the debug_method print:

{"command":"stuff","comment":null,"created_at":"2012-12-11T12:02:41Z",
"creator":null,"emergency_level":null,"file_name":null,"id":16,"is_locked":null,
"is_removed":null,"last_status":null,"next_status":null,"owner_id":null,
"paper_title":null,"receiver":null,"sender":null,"status":"1","suggest":null,
"unit_id":null,"updated_at":"2012-12-11T12:02:41Z",
"uuid":"21403d30-c2c1-4fc8-94ba-36d059fdc170","workflow_id":null}

But the database don't save the "command", ,"status" and "uuid" :

Started POST "/services/" for 127.0.0.1 at 2012-12-11 20:02:41 +0800
Processing by ServicesController#accept as JSON
Parameters: {"{\"id\":\"7e330302-dede-4d2f-bf52-8e90174bb837\",\"method\":\"pd_create\",\"params\":{\"status\":\"1\",\"command\":\"stuff\"}}"=>nil}
(0.0ms)  begin transaction
SQL (0.5ms)  INSERT INTO "processing_documents" ("command", "comment", "created_at", "creator", "emergency_level", "file_name", "is_locked", "is_removed", "last_status", "next_status", "owner_id", "paper_title", "receiver", "sender", "status", "suggest", "unit_id", "updated_at", "uuid", "workflow_id") VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)  [["command", nil], ["comment", nil], ["created_at", Tue, 11 Dec 2012 12:02:41 UTC +00:00], ["creator", nil], ["emergency_level", nil], ["file_name", nil], ["is_locked", nil], ["is_removed", nil], ["last_status", nil], ["next_status", nil], ["owner_id", nil], ["paper_title", nil], ["receiver", nil], ["sender", nil], ["status", nil], ["suggest", nil], ["unit_id", nil], ["updated_at", Tue, 11 Dec 2012 12:02:41 UTC +00:00], ["uuid", nil], ["workflow_id", nil]]
(2.5ms)  commit transaction
Completed 200 OK in 23ms (Views: 0.2ms | ActiveRecord: 3.5ms)

You have see the SQL :SQL (0.5ms) INSERT INTO "processing_documents" ("command", "comment", "created_at", "creator", "emergency_level", "file_name", "is_locked", "is_removed", "last_status", "next_status", "owner_id", "paper_title", "receiver", "sender", "status", "suggest", "unit_id", "updated_at", "uuid", "workflow_id") VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?) [["command", nil], ["comment", nil], ["created_at", Tue, 11 Dec 2012 12:02:41 UTC +00:00], ["creator", nil], ["emergency_level", nil], ["file_name", nil], ["is_locked", nil], ["is_removed", nil], ["last_status", nil], ["next_status", nil], ["owner_id", nil], ["paper_title", nil], ["receiver", nil], ["sender", nil], ["status", nil], ["suggest", nil], ["unit_id", nil], ["updated_at", Tue, 11 Dec 2012 12:02:41 UTC +00:00], ["uuid", nil], ["workflow_id", nil]]

score 2 · Accepted Answer · edited May 23 '17 at 12:12

Why do you call attr_accessor on your model attributes?

attr_accessor :command, :comment, :creator, :emergency_level, :file_name, :is_locked, :is_removed, :last_status, :next_status, :owner_id, :paper_title, :receiver, :sender, :status, :suggest, :unit_id, :uuid, :workflow_id

These are creating accessor methods which set instance variables, e.g. attr_accessor :command does the equivalent of creating a method like this:

def command
  @command
end

def self.command=(value)
  @command = value
end

So what is happening in your code right now is that when you call pd_now.send("#{k}=", v) on each key/value in the hash, instance variables are being set rather than database attributes. That is why you are not seeing the attributes in the SQL generated after you call save.

To fix this, just remove the attr_accessor line in your model.

Ref: Why use Ruby's attr_accessor, attr_reader and attr_writer?

Thank you very much!! But I can't understand the difference between `attr_accessor` of Ruby and `attr_accessible` of Rails. — Ghjhdf, Dec 11 '12 at 12:47
There is a lot of confusion about these two methods, they in fact do very different things. See e.g.: http://stackoverflow.com/questions/4700785/using-attr-accessor-and-attr-accessible-on-the-same-field http://stackoverflow.com/questions/3136420/difference-between-attr-accessor-and-attr-accessible — Chris Salzberg, Dec 11 '12 at 13:39

Why does the "save" return true, but database has a void record?

1 Answers1