MongoDB: output 'id' instead of '_id'

Given you're using Mongoose, you can use 'virtuals', which are essentially fake fields that Mongoose creates. They're not stored in the DB, they just get populated at run time:

// Duplicate the ID field.
Schema.virtual('id').get(function(){
    return this._id.toHexString();
});

// Ensure virtual fields are serialised.
Schema.set('toJSON', {
    virtuals: true
});

Any time toJSON is called on the Model you create from this Schema, it will include an 'id' field that matches the _id field Mongo generates. Likewise you can set the behaviour for toObject in the same way.

See:

http://mongoosejs.com/docs/api.html
http://mongoosejs.com/docs/guide.html#toJSON
http://mongoosejs.com/docs/guide.html#toObject

You can abstract this into a BaseSchema all your models then extend/invoke to keep the logic in one place. I wrote the above while creating an Ember/Node/Mongoose app, since Ember really prefers to have an 'id' field to work with.

As of Mongoose v4.0 part of this functionality is supported out of the box. It's no longer required to manually add a virtual id field as explained by @Pascal Zajac.

Mongoose assigns each of your schemas an id virtual getter by default which returns the documents _id field cast to a string, or in the case of ObjectIds, its hexString. If you don't want an id getter added to your schema, you may disable it passing this option at schema construction time. Source

However, to export this field to JSON, it's still required to enable serialization of virtual fields:

Schema.set('toJSON', {
    virtuals: true
});

I create a toClient() method on my models where I do this. It's also a good place to rename/remove other attributes you don't want to send to the client:

Schema.method('toClient', function() {
    var obj = this.toObject();

    //Rename fields
    obj.id = obj._id;
    delete obj._id;

    return obj;
});

I used this :

schema.set('toJSON', {
  virtuals: true,
  versionKey:false,
  transform: function (doc, ret) {   delete ret._id  }
});

I think it would be great if they automatically suppress _id when virtuals is true.

Here is an alternative version of the answer provided by @user3087827. If you find that schema.options.toJSON is undefined then you can use:

schema.set('toJSON', {
     transform: function (doc, ret, options) {
         ret.id = ret._id;
         delete ret._id;
         delete ret.__v;
     }
});

MongoDB: output 'id' instead of '_id'

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