Transform an array of documents using mongoose

Question

I am running a special query in which I want transform the results after.

User.find({}, function(err, users) {
  // I want to remove/add some properties from/to each user here
});

Is there a way to transform an array of documents? Also this is a special case so I do not want to apply a transformation to the Schema, which I think would transform each document like I want, but would also affect all other queries to the User model.

Basically I want the ability to perform a one time transformation on the array of docs returned.

User.find({}, function(err, users) {
  // I want to remove/add some properties to each user here
  users.toJSON({transform: function(doc,ret,options) { /* do tranform*/ });
  // That will not work as I get an error that toJSON is not defined for that
  // array that was returned.
});

I might be able to fake it out by adding a transformation right before I query and then removing that transformation when the query is complete, but that is a pretty bad hack IMHO.

Ideas? Did I miss something in the docs?

JohnnyHK · Accepted Answer · 2013-07-22 19:34:17Z

7

You can use a lean query so that an array of plain JS objects are returned from the query and then use map to transform the array:

User.find({}).lean().exec(err, users) {
    users = users.map(function(user) {
        // transform user into newuser as needed.
        ...
        return newuser;
    });
});

edited Jul 22, 2013 at 19:34

answered Jul 22, 2013 at 19:22

JohnnyHK

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5 Comments

lostintranslation Over a year ago

Works great, thanks. Hoping there was a way to transform each object before I get the array back. In the end its the same loop regardless just on my end instead of mongoose.

Nate Over a year ago

Note: lean has consequences other than turning a query into plain JS objects, such as getting rid of virtuals, methods, etc. What I needed was just to use the toObject() method on the items in the query (using map) instead.

rakesh kashyap Over a year ago

@Nate can you please help me in understanding how to use toObject() on an array of documents.

Nate Over a year ago

@rakeshkashyap: var usersObj = users.map(function (user) { return user.toObject(); });

Nate Over a year ago

@rakeshkashyap Or, these days: let usersObj = users.map(user => user.toObject());

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