// User schema
{
    username: {
      type: String,
      required: true,
      unique: true
    },
    email: {
      type: String,
      required: true,
      unique: true
    },
    password: {
      type: String,
      required: true
    }
}

// Account schema
{
  name: {
    type: String,
    required: true,
  },
  user: {
    type: Schema.Types.ObjectId,
    ref: 'User',
    required: true
  },
  transactions: [{
    value: {
      type: Schema.Types.Decimal128,
      required: true
    },
    category: {
      type: Schema.Types.ObjectId,
      ref: 'Category',
      required: true
    },
    description: {
      type: String,
      required: true
    }
  }]
}

// Category schema
{
  name: {
    type: String,
    required: true
  },
  type: {
    type: String,
    required: true
  },
  user: {
    type: Schema.Types.ObjectId,
    ref: 'User',
    require: true
  },
  icon: {
    type: String
  }
}