How do you iterate over Mongoose model properties within a middleware function?

Question

I'm attempting to iterate over fields in a mongoose model within a middleware function. The current context this is the model object itself. So I have a function in which the context is a Javascript object like this:

{
  lastName: 'Wilkens',
  firstName: 'Elepart',
  name: 'Elepart Wilkens',
  username: 'eK',
  bio: '<script>alert(\'this is a hack!!\')',
  _id: 53b17dd0e8c5af50c1d73bc6,
  language: 'en',
  country: 'USA',
  online: true
}

I want to iterate over this object (which is represented in the current function with this). Every time I attempt to iterate with loops, it prints out values that look like internal Javascript metadata. Is it possible to iterate over this within a function if this represents an object?

Here's the actual middleware function:

userSchema.pre('save', function (next) {
    console.log(this); // This prints precisely the same object I have copied above

    var fields = Object.keys(this);

    for(var i = 0; i < fields.length; i++) {
        console.log(this[fields[i]]);
    }

    for(var key in this) {
      if(this.hasOwnProperty(key)) {
        console.log(this[key]);
      }
    }
});

And the output is:

{ 
 strictMode: true,
 selected: undefined,
 shardval: undefined,
 saveError: undefined,
 validationError: undefined,
 adhocPaths: undefined,
 removing: undefined,
 inserting: undefined,
 version: undefined,
 getters: {},
 _id: undefined,
 populate: undefined,
 populated: undefined,
 wasPopulated: false,
 scope: undefined,
 activePaths: 
   { paths: 
      { username: 'modify',
        firstName: 'modify',
        name: 'modify',
        online: 'default',
        country: 'default',
        language: 'default',
        _id: 'default',
        bio: 'modify',
        lastName: 'modify' },
     states: { default: [Object], init: {}, modify: [Object], require: {} },
     stateNames: [ 'require', 'modify', 'init', 'default' ],
     map: [Function] },
  ownerDocument: undefined,
  fullPath: undefined }
true
undefined
0
{ online: true,
  country: 'USA',
  language: 'en',
  _id: 53b1825a00ed9af7c12eedf9,
  bio: '<script>alert(\'this is a hack!!\')',
  username: 'yK',
  name: 'Yershay Wilkens',
  firstName: 'Yershay',
  lastName: 'Wilkens' }
{ save: 
   [ { [Function] isAsync: false },
     { [Function: checkForExistingErrors] isAsync: false },
     { [Function: validation] isAsync: false },
     { [Function] isAsync: false },
     { [Function] isAsync: false } ],
  validate: [ { [Function] isAsync: false } ] }
{ save: [], validate: [] }
{ [Function] numAsyncPres: 0 }
{ [Function] numAsyncPres: 0 }
{}

Without more code we can't help you. Though here is an example of how it could work: http://jsbin.com/gomisuyu/1/ — Yoshi, Jun 30 '14 at 15:23
I've added more code. A JSfiddle wouldn't be as helpful since this is all with Mongoose, so it be a bit hard to replicate in the browser. — Glen Selle, Jun 30 '14 at 15:25
When iterating over an object (not an array) try using "for in" `for ( key in object )` as well as `hasOwnProperty` as answered here http://stackoverflow.com/questions/684672/loop-through-javascript-object — tastybytes, Jun 30 '14 at 15:27
Ok, but Object.keys() returns an array if I'm not mistaken, right? — Glen Selle, Jun 30 '14 at 15:27

score 6 · Answer 1 · edited Nov 24 '15 at 16:55

6

You're using integer indexes instead of the string references from the fields array. It should be:

var fields = Object.keys(this);

for(var i = 0; i < fields.length; i++) {
    console.log(this[fields[i]]);
}

(e.g., you were doing this[1], this[2], instead of this[fields[1]])

edited Nov 24 '15 at 16:55

Glen Selle

3,966
4
37
59

answered Jun 30 '14 at 15:28

psantiago

695
6
16

Good catch, but I just updated the question...I still get the same output, basically JS Jibberish when I do this[fields[i]] – Glen Selle Jun 30 '14 at 15:36
4

@Glen Try changing the first line to: `var fields = Object.keys(this.toObject());` – JohnnyHK Jun 30 '14 at 17:57
Thanks anyways, I found that using Object.keys() with this._doc was the best way to get only the properties of the model and not all the JS stuff that I seemed to be getting by using `this` alone. – Glen Selle Jun 30 '14 at 18:01

score 6 · Answer 2 · answered Sep 15 '17 at 12:27

6

@JohnnyHK's comment worked for me:

const user = new User();
const schemaKeys = Object.keys(user.toObject());

answered Sep 15 '17 at 12:27

Steve Brush

2,911
1
23
15

1

This should be the marked answer rather than accessing private properties via `_doc`. – philosopher Nov 08 '20 at 07:02

Glen Selle · Accepted Answer · 2014-06-30T18:06:09.527

I found a slightly different way to accomplish what I wanted which was to iterate over the model properties of a Mongoose model within a middleware function. This uses async.js, but you could refactor it to use a generic JS loop or any other control flow library. The key is to get an array of the document's fields, then you can iterate over those and get/set the values using the current context with this. As far as I know, this will not coerce non-string values into strings. I've tested it with strings, numbers, booleans and objectIds and they are successfully saved as their original data types.

yourSchema.pre('save', function (next) {
  var self = this;

  // Get the document's fields
  var fields = Object.keys(this._doc);

  // Do whatever you want for each field
  async.each(fields, function(field, cb) {
    self[field] = validator.escape(self[field]);
    cb();
  }, function(err){
    next();
  });
});

How do you iterate over Mongoose model properties within a middleware function?

3 Answers3