Persisting timestamp field as Date or Long?

Question

I need a consensus on the practice of persisting timestamps, specifically on the pros & cons of using java.util.Date compared to using long.

Scope of this discussion:

• Performance
• Querying Flexibility (e.g. date range)
• Any hazards in coding and querying
• Portability (e.g. migration to other DB)

About myself: I consider myself to be a beginner in JPA, dabbling in it once in a while, not being able to apply it into production level projects until now. In my current project, I commit myself to use ObjectDB (embedded) through JPA calls.

Answer 1

The following class demonstrates 3 possible methods for persisting timestamps in JPA:

@Entity
public class Timestamps {
    private java.sql.Timestamp ts1;
    private @Temporal(TemporalType.TIMESTAMP) java.util.Date ts2;
    private long ts3;
    :
}

Regarding performance and memory consumption, ts3 is a bit more efficient.

ts3 may be less convenient to use than ts1 and ts2 (in ObjectDB Database Explorer, reports, etc.).

Basic queries such as retrieval by date range are supported for all the three, but extracting date and time parts (YEAR, MONTH, etc.) in queries is not supported for ts3.

All these forms are expected to be portable.

ts1 and ts2 are practically equivalent.

More details are provided in the ObjectDB manual.