support dynamic insert

hi, bob:

When calling db.save(obj) for insert operations, it would be helpful if the insert statement were dynamically generated based on the non-null properties of obj, rather than using a predefined insert statement with all the fields included.
I understand this might impact performance slightly; however, this approach would leverage database-default-column-values effectively. If some columns are omitted from the insert statement, the database could automatically assign default values defined for those columns.
For reference, Hibernate provides a similar feature through the @DynamicInsert annotation. See: https://docs.jboss.org/hibernate/orm/6.5/javadocs/org/hibernate/annotations/DynamicInsert.html
Alternatively, if complete SQL insert statements are preferred, the framework could explicitly include the DEFAULT keyword for such columns in the dynamically generated SQL statements.

Start at the db.save(obj) insert path and inspect how predefined insert statements are generated. Done means inserts can omit null properties so database defaults apply, with the preferred handling of omitted columns or the DEFAULT keyword decided.