Question

I’m working on a project which will post periodic XML updates for users. I’m attempting to suppress information which hasn’t changed since the last update.

Within node.js, I have assembled a user object which will be used to generate the XML:

users = 
  # actual application has 25 properties per user
  [
    {
      USERID: 150927,
      EMAIL: '[e-mail]',
      FIRSTNAME: 'Irving',
      LASTNAME: 'Block',
      COLOR: 'Green'
    },
    {
      USERID: 1246007,
      EMAIL: '[e-mail]',
      FIRSTNAME: 'Adler',
      LASTNAME: 'Allen',
      COLOR: 'Blue'
    },
    {
      CLKEY: 1248350,
      EMAIL: '[e-mail]',
      FIRSTNAME: 'Walter',
      LASTNAME: 'Pidgeon',
      COLOR: 'Red'
    }
  ]

I also have an object loaded which helps map user data to the eventual XML fields:

xml_map =
  [
    {
      ID: 1,
      ELEMENT: 'xml_map_assigned_id',
      MAPPPED: 'USERID' 
    },
    {
      ID: 2,
      ELEMENT: 'xml_map_email_address',
      MAPPPED: 'EMAIL' 
    },
    {
      ID: 3,
      ELEMENT: 'xml_map_user_firstname',
      MAPPPED: 'FIRSTNAME' 
    },
    {
      ID: 4,
      ELEMENT: 'xml_map_user_lastname',
      MAPPPED: 'LASTNAME' 
    },
    {
      ID: 5,
      ELEMENT: 'xml_map_user_color',
      MAPPED: 'COLOR'
    }
  ]

Using these objects, I need to compare with the last update, and remove matching properties (since I only want to post updates for data that has changed). Here’s an example of what the last update (stored in the DB) might look like:

# nothing like this is used in the real application
# just showing here to give an idea of what the DB could look like
db_data = 
  [ 
    {
      USERID: 150927,
      EMAIL: '[e-mail]',
      FIRSTNAME: 'IRVING',
      LASTNAME: 'Block',
      COLOR: 'Orange'
    },
    {
      USERID: 1246007,
      EMAIL: '[e-mail]',
      FIRSTNAME: 'Adler',
      LASTNAME: 'Allen',
      COLOR: 'Blue'
    },
    {
      USERID: 1248350,
      EMAIL: '[e-mail]',
      FIRSTNAME: 'Walt',
      LASTNAME: 'Pidgeon',
      COLOR: 'Red'
    }
  ]

Using these examples, I’d like to end up with a User object like this (since only 1 thing has changed for each user):

users_final = 
  [
    {
      USERID: 150927,
      COLOR: 'Orange'
    },
    {
      USERID: 1246007,
      EMAIL: '[e-mail]',
    },
    {
      USERID: 1248350,
      FIRSTNAME: 'Walt',
    }
  ]

And now for the pseudo-code that shows how I’ve been trying to accomplish this:

async = require "async"

handleChanges = (users, map, callback) ->
  sql1 = "select..."
  sql2 = "update..."
  sql3 = "insert..."
  db.query sql1, [], (err, rows, def) ->
    if err? then console.log err
    if rows[0]
      if rows[0].ELEMENT_VALUE.toString() is users[map.MAPPED].toString() 
      # nothing has changed since last update
        db.query sql2, ['Old'], (err, rows, def) ->
          if err? then console.log err
          callback null, map.MAPPED
      else # this value has changed since the last update. Run update query
        db.query sql2, ['New'], (err, rows, def) ->
          if err? then console.log err
          callback null, null
    else # no value has ever been saved for this combo. Run insert query
      db.query sql3, [], (err, rows, def) ->
        if err? then console.log err
        callback null, null

updateStore = (users, callback) ->
  for map in xml_map
    do(map) ->
      handleChanges users, map, (err, del) ->
        if del? then delete r[del]
  callback null, r

async.map users, updateStore, (err, results) ->
  console.log results

This obviously doesn’t work right. I’m sure the updateStore function needs to be doing something different, but I’m at a loss.

Thanks in advance for your help!

Answer 1

I did similar thing in the project, but I use json instead of xml.

What I have done is
retrieve a list of objects from db. and calculate a hash value for each of the object.

users = 
  [
    {
      USERID: 150927,
      EMAIL: '[e-mail]',
      FIRSTNAME: 'Irving',
      LASTNAME: 'Block',
      COLOR: 'Green'
    },
    {
      USERID: 1246007,
      EMAIL: '[e-mail]',
      FIRSTNAME: 'Adler',
      LASTNAME: 'Allen',
      COLOR: 'Blue'
    }
  ]
hash = [
  'c8addc875913a367486ba8343f68e349667e0334',
  'df3d067e876437996237d0fde90466703ea303b9'
]

on the client side, I do compare the each old hash to the new hash. if different I use php.js or underscore.js. php.js can do array_diff to get differents between two object. Of course you can just do array_diff with comparing hash.

If your data structure is nested like this

{
  User: {
    FIRSTNAME: 'Irving',
    LASTNAME: 'Block',
    USERID: 150927
  }
  OtherInfo: {
    EMAIL: '[e-mail]'
  }
}

you can flatten it to following before doing array_diff because array_diff only work on one level.

{
  "User.FIRSTNAME": 'Irving',
  "User.LASTNAME": 'Block',
  "User.USERID": 150927,
  "OtherInfo.EMAIL": '[e-mail]'
}