Rewrites — ASL

Rewrites

A default runs once, on INSERT. A rewrite re-assigns the field on the events you name — the mechanism behind an auto-updating updated_at:

updated_at: datetime {
  default := datetime_current();
  rewrite update := datetime_current();   # events: insert, update (comma-separated)
};

The value may be a builtin function (datetime_current() → now()), a literal, a row-reference column — __new__.<field> / __subject__.<field> (the row being written) or __old__.<field> (the pre-update row, UPDATE only) — or a call to a declared function passing row references and literals:

slug: str { rewrite create, update := __new__.title; };            # NEW."title"
slug: str { rewrite create, update := slugify(__new__.title); };   # slugify(NEW."title")

Events are insert / update; create is accepted as an alias for insert.

A rewrite belongs to the type that declared it, and generates one function per declaring model, named axel_rw_<model>_<serial>. An updated_at rewrite on an abstract Base becomes a single axel_rw_base_1 that every concrete type inheriting it shares — each concrete table gets its own BEFORE trigger that EXECUTEs that one function. A rewrite a concrete type declares itself is a separate function (axel_rw_<that_type>_1), so a type that both inherits and declares rewrites simply gets one trigger per contributing model. See Triggers for the general mechanism.