title: MongoDB: Updating documents using current fields value
body: <p>I have mongodb "Mydb" with collection "users".</p>
  
  <pre><code>export let User = mongoose.model("User", UserSchema);
  
  let UserSchema = new mongoose.Schema({
        phone           : {
          type    : String,
          validate: {
  </code></pre>
  
  <p>Now I want to update field "phone" replacing whitespaces (for example). I try to use following:</p>
  
  <pre><code>User.update({}, {$set : {'phone': //here is my problem}},
  {multi: true, upsert:false}, () =&gt; next());
  </code></pre>
  
  <p>How can I get current "phone" value to replace it? (I use mongoose-migrate)</p>
  
  <p>As I said I try to use mongoose-migration module, so I've created new migration file like this:                                                                          </p>
  
  <pre><code>    'use strict'
  const mongoose = require('mongoose');
  import { User, dbConnection } from '../db/index'
  
  export function up(next) {
  User.update({}, {$set : {'phone': this.phone}}, {multi: true, upsert:false}, () =&gt; next());
  }
  
  
  export function down(next) {
      next();
  }
  </code></pre>
  
  <p>where User:</p>
  
  <pre><code>export let User = mongoose.model("User", UserSchema);
  </code></pre>