What is the Expense Object Model?

The Expense model represents individual financial expenses in the Finance Tracker application. It includes attributes such as name, amount, category, and date, allowing users to track and categorize their spending effectively.

Database Fields

The Expense model includes the following fields, as defined in the database migration:

• name:
  • Data Type: String
  • Description: The name or description of the expense (e.g., "Internet Bill").
  • Validation: Required (null: false).
• amount:
  • Data Type: Decimal
  • Precision: 12, Scale: 2
    • Precision (12): The total number of digits, including those before and after the decimal point. For example, 9999999999.99 is the largest number possible with this precision.
    • Scale (2): The number of digits allowed after the decimal point. For example, numbers like 12345.67 or 0.99 are valid with this scale.
    • Why these values? A precision of 12 supports amounts up to 10 billion (9999999999.99), and a scale of 2 ensures accurate representation of cents or fractional currency units without rounding errors.
  • Description: The monetary amount of the expense.
  • Validation: Required (null: false), greater than 0.
• category:
  • Data Type: String
  • Description: The category for the expense (e.g., "Utilities").
  • Validation: Optional (null: true).
• date:
  • Data Type: Date
  • Description: The date of the expense.
  • Validation: Required (null: false).
• Timestamps:
  • Data Type: created_at, updated_at (automatically added by Rails).

Model Validations

The Expense model includes the following validations to ensure data integrity:

class Expense < ApplicationRecord
  validates :name, presence: true
  validates :amount, presence: true, numericality: { greater_than: 0 }
  validates :date, presence: true
end

• Presence Validations: Ensures name, amount, and date are present.
• Numericality Validation: Ensures amount is greater than 0.