const Schema = mongoose.Schema({
  username: {
    type: String,
    unique: true,
    required: true
  },

  password: {
    type: String,
    required: true
  },

  clients: [{}]
});

const Schema = mongoose.Schema({
  name: {
    type: String,
    required: true
  },

  email: {
    type: String,
    required: true,
    unique: true
  },

  phone: {
    type: String,
    required: true
  },

  budgets: [{}]
});

const Schema = mongoose.Schema({
  client: {
    type: String,
    required: true
  },

  state: {
    type: String,
    required: true
  },

  title: {
    type: String,
    required: true
  },

  total_price: {
    type: Number,
    required: true
  },

  items: [{}]
});

User.findOne({ 'username': req.body.username }, (error, user) => {
    if (error) return res.status(400).json(error);
    else {
      client.save(error => {
        if (error) return res.status(400).json(error);
        else {
          User.findOneAndUpdate(
            { 'username': req.body.username },
            { $push: { "clients": client } },
            { upsert: false },
            (error) => {
              if (error) return res.status(400).json(error);
            }
          )
          res.status(200).json({ success: true, message: 'Client registered
  successfully '});
        }
      })
    }
  })