precision of SQL time and timestamp types

[gavinking]

JPA provides no way to specify the precision of SQL time and timestamp types (in fractional seconds).

For some time Hibernate has been abusing the precision member of the @Column annotation for this, but this has a bit of a problem in that its default value is precision=0 [which is actually intended to be interpreted as null] and 0 is both (a) a meaningful/useful value, and (b) not the best default for a timestamp.

Therefore, I think we should formalize something in the JPA spec, by defining:

1. the default precision for a time (0 digits of fractional second precision, IMO)
2. the default precision for a timestamp (3-6 digits of fractional second precision, depending on the database, IMO)
3. a way for the user to explicitly specify the precision.

Now, there's three options I can think of for part 3:

• change the default of the precision member of the @Column to -1, so that the defaulted value can be interpreted based on the type,
• add a fractionalSecondsPrecision member to @Column, or
• introduce a new @FractionalSeconds annotation.

The disadvantage of the first option is it's in principle a breaking change.

[sebersole]

introduce a new @FractionalSeconds annotation.

:+1:

This is the approach we are taking in Hibernate fwiw - https://hibernate.atlassian.net/browse/HHH-17575