Fix BC year handling in postgres

[nanaya]

Current method is broken: it simply converts astronomical year (what ruby uses) to BC era year (what postgres uses) even though they're off by one, starts from 1, and year 0 AD does not exist which causes postgres to return error.

• 0000-01-01 => 0001-01-01 BC
• 0000-02-29 => 0001-02-29 BC

For example, just try searching any model's created_at with Date.new(0) (0001-01-01 BC) or Date.new(-4,2,29) (0005-02-29 BC).

[nanaya]

Sorry, I made several mistakes and triggered many CI builds.

[matthewd]

LGTM; can you add some tests to ensure it stays fixed? 😄

[nanaya]

Test added. The fix feels really ugly though.

Ideally:

• assignment using something like TO_TIMESTAMP($date, 'YYYY-MM-DD')
• and type casting done using something that actually understands BC date string format (or alternatively somehow tell postgres to use astronomical year)

[matthewd]

I think it's fine; casting & quoting is the right place to translate between two different calendar systems.