Scope

Support the temporal types that denote a date, or a time of day, rather than a point on the timeline:* java.time.LocalDate

• java.time.LocalTime
• java.time.LocalDateTime
• java.time.OffsetTime
• java.sql.Date
• java.sql.Time
• @Temporal(DATE) and @Temporal(TIME) on java.util.Date

All of these are rejected at boot today.

The design question

MongoDB has no date-only and no time-only type. BSON Date is signed 64-bit milliseconds since the Unix epoch, in UTC, with no zone. So each type in scope needs an encoding decision, and the decision is a trade-off rather than a detail.

Encoding them as BSON Date, at midnight UTC for a date and on the epoch day for a time of day, keeps them comparable, sortable and indexable, and keeps them usable by the datetime operators in HIBERNATE-88, which accept only a Date operand. The cost is documents that read as datetimes to anything outside Hibernate, with a midnight or a 1970 date that carries no meaning.

The alternative encodings look more faithful in a document and forfeit all of that: an ISO-8601 string, an integer day number, or an integer nanosecond-of-day. String encodings of ISO-8601 dates do sort correctly, but they cannot be fed to any datetime operator without conversion, and a mixed encoding across temporal types would mean the translator can no longer treat temporal columns uniformly.

OffsetTime carries an offset in addition to a time of day, so it also needs a time zone storage decision, in the way OffsetDateTime does.