Mocking Temporal Database Constraints (start_date \< end_date)

Relational databases don't just enforce data types; they enforce logic. One of the most common business rules is temporal logic: a subscription must end after it begins, or a booking checkout must occur after check-in.

Generating mock data that respects these cross-column temporal constraints is notoriously difficult. Here is why standard date generators fail, and how to seed time-bound data correctly.

The Code Problem: The Time Paradox

Look at a standard booking or subscription table using a CHECK constraint:

CREATE TABLE hotel_bookings (

booking_id UUID PRIMARY KEY,

guest_id UUID NOT NULL,

check_in_date DATE NOT NULL,

check_out_date DATE NOT NULL,

-- The Temporal Constraint

CONSTRAINT valid_stay_dates CHECK (check_out_date > check_in_date)

);

Why Generic Scripts Fail

If you use a tool like Faker.js to generate check_in_date and check_out_date independently, they are completely unaware of each other.

• ✓Row 1: Check-in: 2026-05-10, Check-out: 2026-05-15 (Success)
• ✓Row 2: Check-in: 2026-08-20, Check-out: 2026-03-11 (Failure)

The database will immediately throw a constraint violation on Row 2, crashing the entire seed process. Developers usually "fix" this by temporarily disabling constraints in their test environments—which completely defeats the purpose of integration testing.

The Aphelion Solution

Aphelion automatically reads CHECK constraints during introspection. It understands that check_out_date is dependent on check_in_date. It generates the check-in date first, and then deterministically adds a positive integer of days to ensure the check-out date perfectly satisfies the temporal constraint.

Recipe: Seeding Temporal Constraints

# 1. Introspect to capture CHECK constraints

aphelion introspect postgres://admin:password@localhost:5432/booking_db

# 2. Generate mathematically valid bookings

aphelion generate --table hotel_bookings --rows 50000 --seed 2026

Result: 50,000 rows generated in milliseconds. Zero time paradoxes. Zero constraint violations.