Compare only DATE portion of a datetime field in Expression builder

Question

Hi! All,
This may be a simple question, but I couldn't find the answer. I have a query where I want to say :
Expression exp = exp1.get("startDateTime").equal(pDate);
here pDate is a java.util.Date class with a time stamp.
I wish to basically compare just the DATE portion of the value stored in the data base with only the DATE portion of "pDate" and ignore the time component.
How do I do this in expression builder?
By the way we are on Toplink 9.0.4.5
Thanks

Answer 1

There are a couple of ways to accomplish this. You could use between(beginningOfDay,endOfDay) where beginning of day is 12:00:00am on the date specified in pDate and end of day is 11:59:59pm on pDate. Or you could consider using a combination of dateName(), datePart(), and/or truncateDate() expressions to compare at the day, month, year level. I am not sure which would give you better performance, so you might need to do some testing to verify.
In the first case, create beginningOfDay and endOfDay based upon the date housed in pDate. Then:
Expression selectionCriteria = exp1.get("startDateTime").between(beginningOfDay,endOfDay);
In the second case, there would be a little more code to write:
Expression startDateTimeExp = exp1.get("startDateTime");
Expression dayExp = startDateTimeExp.datePart("day");
Expression monthExp = startDateTimeExp.datePart("month");
Expression yearExp = startDateTimeExp.datePart("year");
int desiredDay = get day of month from pDate;
int desiredMonth = get month of year from pDate;
int desiredYear = get year from pDate;
Expression selectionCriteria = dayExp.equal(desiredDay).and(monthExp.equal(desiredMonth)).and(yearExp.equal(desiredYear));
Check out the TopLink API docs on the Expression class for more details on what these Expression building methods do : http://download-west.oracle.com/docs/cd/B10464_05/web.904/b10491/index.html
Hope that helps,
Doug