Rounding issues storing java.util.Date into MySQL datetime

Question

MySQL DB column:

PLANNING_DATE datetime

Java field:

private java.util.Date planningDate;

Hibernate mapping:

<property name="planningDate" column="PLANNING_DATE" type="timestamp" not-null="true"/>

The problem: PLANNING_DATE in MySQL DB does not always match planningDate field. Sometimes, it gets an offset of 1 second. Is this a rounding issue?

Answer 1

Ok, I think it's because in MySQL >= 5.6.4 they changed DATETIME to truncate fractional seconds by default. I updated our table schemas to use the new DATETIME(6). I'll check if this was indeed the cause.

http://dev.mysql.com/doc/refman/5.6/en/fractional-seconds.html

EDIT: Actually, DATETIME in MySQL >= 5.6.4 (which is equivalent to DATETIME(0)) rounds to seconds precision, as opposed to DATE in Oracle which truncates. Added a custom Hibernate type to do truncation instead of rounding and the problem was solved.

Answer 2

I don't know much about either MySql or Hibernate, but here goes…

A) You probably should be using java.sql.Date. It is a thin subclass of java.util.Date, meant fir use with JDBC.

B) The MySql doc do mention that their date-time types do not store the fractional part of a second. So perhaps there is rounding happening. But the docs mention truncation.