var UserSchema = Schema({
    firstName: {
        type: String,
        required: true
    },
    secondName: String,
    lastName: {
        type: String,
        required: true
    },
    email: {
        type: String,
        unique: true,
        required: true
    },
    password: {
        type: String,
        required: true
    },
    status: {
        type: String,
        required: true
    },
    roles: [{
        type: Schema.ObjectId,
        ref: 'Role'
    }],

    publications: [{
        title: {
            type: String,

        },
        description: String,
        status: {
            type: String,

        },
        createdAt: {
            type: Date
        },
        updatedAt: {
            type: Date,
            default: Date.now()
        },

        pictures: [{
            name: String
        }],

        categories: [{
            type: Schema.Types.ObjectId,
            refPath: 'Category.subcategories'
        }],

var CategorySchema = Schema({
    name: String,
    subcategories: [{
        name: String
    }]
});

categories: [{
                type: Schema.Types.ObjectId,
                refPath: 'Category.subcategories'
            }],

"users": [
        {
            "roles": [],
            "publications": [
                {
                    "updatedAt": "2018-04-30T03:23:11.921Z",
                    "categories": [
                        "5ae4a8b0a7510e3bd80917db",
                        "5ae4a8b0a7510e3bd80917da"
                    ],
                    ...

{
    "categories": [
        {
            "subcategories": [
                {
                    "_id": "5ae4a8b0a7510e3bd80917db",
                    "name": "Decoracion"
                },
                {
                    "_id": "5ae4a8b0a7510e3bd80917da",
                    "name": "Electrodomésticos"
                },
                {
                    "_id": "5ae4a8b0a7510e3bd80917d9",
                    "name": "Cocina"
                },
                {
                    "_id": "5ae4a8b0a7510e3bd80917d8",
                    "name": "Muebles"
                }
            ],
            "_id": "5ae4a8b0a7510e3bd80917d7",
            "name": "Hogar",
            "__v": 0
...

User.populate(users, {
            path: 'publications.categories'
        }, (err, users) => {

            if (err) {
                res.status(500).send({
                    message: "Error en la peticion"
                });
                return;
            }

            if (!users) {
                res.status(404).send({
                    message: "User no encontrado"
                });
                return;
            }


            res.status(200).send({
                users
            });

var userSchema = new Schema({
  name: String,
  connections: [{
    kind: String,
    item: { type: ObjectId, refPath: 'connections.kind' }
  }]
});

var organizationSchema = new Schema({ name: String, kind: String });

var User = mongoose.model('User', userSchema);
var Organization = mongoose.model('Organization', organizationSchema);