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Re: [eclipselink-users] Caching and Relational Objects
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I'm not sure what you are trying to do?
The cache will cache anything you read, so if you read it again (by primary
key) you avoid accessing the database, and (by query) avoid rebuilding the
object and its relationships.
What is your save() doing? Are you calling persist()? Persist is for new
objects, it inserts the object into the database. You cannot insert an
object if it already exists. If the object exists, just read the object
using find().
Are you trying to put an object into the EclipseLink cache from another
source? Where did you get this object from?
Bhaskar Maddala wrote:
>
> Hello,
>
> I have the following domain objects (retained only the relevant
> information - or what I thought to be relevant)
>
> @Entity
> @Table(name = "RSRCHOUR")
> public class ResourceHour
> implements Serializable {
> private Integer m_hourId;
> private TimesheetPeriod m_timesheetPeriod;
>
> @TableGenerator(name = "rsrchour_rsrc_hr_id", table = "NEXTKEY",
> pkColumnValue = "rsrchour_rsrc_hr_id", allocationSize = 1, pkColumnName =
> "KEY_NAME", valueColumnName = "KEY_SEQ_NUM")
> @Id
> @GeneratedValue(strategy = TABLE, generator = "rsrchour_rsrc_hr_id")
> @Column(name = "RSRC_HR_ID")
> public Integer getHourId() {
> return m_hourId;
> }
> public void setHourId(Integer hourId){
> m_hourId = hourId;
> }
>
> @OneToOne(fetch = FetchType.LAZY)
> @JoinColumn(name="TS_ID", referencedColumnName="TS_ID")
> public TimesheetPeriod getTimesheetPeriod() {
> return m_timesheetPeriod;
> }
> public void setTimesheetPeriod(TimesheetPeriod timesheetPeriod) {
> m_timesheetPeriod = timesheetPeriod;
> }
> }
>
> @Entity
> @Table(name = "TSDATES")
> public class TimesheetPeriod
> implements Serializable {
> private Integer m_timesheetPeriodId;
> private Date m_startDate;
> private Date m_endDate;
>
> @TableGenerator(name = "timesht_ts_id", table = "NEXTKEY",
> pkColumnValue
> = "timesht_ts_id", allocationSize = 1, pkColumnName = "KEY_NAME",
> valueColumnName = "KEY_SEQ_NUM")
> @Id
> @Column(name = "TS_ID", nullable = false, length = 10)
> public Integer getTimesheetPeriodId() {
> return m_timesheetPeriodId;
> }
> public void setTimesheetPeriodId(Integer timesheetPeriodId) {
> m_timesheetPeriodId = timesheetPeriodId;
> }
>
> @Temporal(TemporalType.DATE)
> @Column(name = "END_DATE", nullable = false)
> public Date getEndDate(){
> return m_endDate;
> }
> public void setEndDate(Date endDate){
> m_endDate = endDate;
> }
>
> @Temporal(TemporalType.DATE)
> @Column(name = "START_DATE", nullable = false)
> public Date getStartDate(){
> return m_startDate;
> }
> public void setStartDate(Date startDate){
> m_startDate = startDate;
> }
>
> @Override
> public int hashCode() {
> return (m_timesheetPeriodId == null) ? 0 :
> m_timesheetPeriodId.intValue();
> }
> @Override
> public boolean equals(Object obj) {
> if (this == obj) {
> return true;
> }
> if (obj == null) {
> return false;
> }
> if (getClass() != obj.getClass()) {
> return false;
> }
> final TimesheetPeriod other = (TimesheetPeriod)obj;
> if (m_timesheetPeriodId == null) {
> if (other.m_timesheetPeriodId != null) {
> return false;
> }
> }
> else if (!m_timesheetPeriodId.equals(other.m_timesheetPeriodId)) {
> return false;
> }
> return true;
> }
> }
>
> // I exercise these domain objects as follows
> TimesheetPeriod tp = new TimesheetPeriod();
> tp.setTimesheetPeriodId(Integer.valueOf(timesheetTask.getTsId())); // only
> setting the key field, ignoring other fields
> ResourceHour hour = new ResourceHour();
> hour.setTimesheetPeriod(tp);
> m_hoursDao.save(hour); // JPA call to save the domain object
>
> // assuming an initial cache state of empty, I end up with the following
> cache state
> UnitOfWorkIdentityMap for: TimesheetPeriod
> Key: [10] Identity Hash Code: 20015579 Object:
> TimesheetPeriod[TimesheetPeriodId: 10 StartDate: null EndDate: null
>
> I then load the TimesheetPeriod using a Query, the timesheet period
> returned
> is the one from cache. I noticed that a "database query is issued" to load
> the actual database row and prior to using ObjectBuilder a check is made
> in
> the cache to retreive an existing object if available in the cache.
>
>>From the database schema I know that both startdate and enddate fields
> cannot be null. I therefore use them field values without a check which
> results in a NPE.
>
> I can think of only 1 fix which is to load the TimesheetPeriod rather than
> creating one in memory and setting the primary key as I have at this time.
>
> Questions:
> * What is the expected/accepted usage pattern with regards to cache, is
> the
> use case of creating objects in memory with only primary key fields
> invalid/incorrect?
> * When using a query to load from the database eclipselink always issues a
> query and only uses the results (AbstractRow instances) to use primary key
> references to retrieve objects from cache, avoidinh new object creation,
> am
> I doing something wrong or can I get eclipselink to make proper use of the
> cache avoiding network round trips (database queries) when loading using
> queries?
> * What is the correct implementation for hashcode and equals for domain
> objects, should they just be off primary key fields or all fields, will
> using all fields help with my caching issue, I am guessing not as eclipse
> link seems to use primary key field equals (via ClassDescriptor instances)
> and not the hashcode/equals combination for its cache.
>
> Any other fixes are welcome
>
> Thanks
> Bhaskar
>
>
-----
---
http://wiki.eclipse.org/User:James.sutherland.oracle.com James Sutherland
http://www.eclipse.org/eclipselink/
EclipseLink , http://www.oracle.com/technology/products/ias/toplink/
TopLink
Wiki: http://wiki.eclipse.org/EclipseLink EclipseLink ,
http://wiki.oracle.com/page/TopLink TopLink
Forums: http://forums.oracle.com/forums/forum.jspa?forumID=48 TopLink ,
http://www.nabble.com/EclipseLink-f26430.html EclipseLink
Book: http://en.wikibooks.org/wiki/Java_Persistence Java Persistence
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