On Feb 23, 2007, at 7:49 PM, Pinaki Poddar wrote:
One way to realize a owner object with a partially filled multi-cardinality relationship is to expand fetchplan concept. For example, if we consider a Department of 100 Employees of which only 20 are oldtimers, then a query can select the particular Department fromthe datastore but to realize that Department as a Java object in memory with only 20 senior Employees in _employees collection will need to tunethe fetch plan acconrdingly. In JDO, fetch plan is specified to certain details to extract a subset of native states and subset of relationships. JPA does not yet specify fetch plan, but OpenJPA does via @FetchGroup extension. Howevercurrently, no filtering criterion is applied to filter the content whilea particular relationship path is traversed. It is a all-or-nothing affair. Either Department is fetched with all its 100 Employees or the Employees relation is not traversed at all. The only control available now is to specify which native states and relationship will be considered for fetching and in case of recursive relationship how many times a particular relation path will be traversed. Essentially query and fecth paths are working in conjunction -- query selects the root object and fetch plan decides which subset of theclosure of this root object is realized in memory. It will surely be a useful feature to consider expanding fetch plan with filtering criteria.
Sorry to disagree. If you fetch Department instances, I think you always want the _employees collection to contain all the related Employees. You never want a filtered collection unless you provide a filter via some Java behavior.
In the query case, you want to get references to the filtered instances but there's no connection to the _employees field of the department.
This is a good thing. Craig
Pinaki Poddar BEA Systems 415.402.7317 -----Original Message----- From: Patrick Linskey Sent: Friday, February 23, 2007 4:37 PM To: open-jpa-dev@incubator.apache.org Subject: RE: possible to write a JPA Query to that filters both an Entity and its relationship entities? I would expect that your query would return the unfiltered employees collection. But I have not run any tests. In other words, I would expect that the oldtimers collection would be the full set of employees for each dept that had any oldtimers >= 15.That said, I don't think that your interpretation is necessarily wrong.Just not my expectation. -Patrick -- Patrick Linskey BEA Systems, Inc.______________________________________________________________________ _ Notice: This email message, together with any attachments, may contain information of BEA Systems, Inc., its subsidiaries and affiliated entities, that may be confidential, proprietary, copyrighted and/or legally privileged, and is intended solely for the use of the individual or entity named in this message. If you are not the intended recipient, and have received this message in error, please immediately return thisby email and then delete it.-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Friday, February 23, 2007 4:14 PM To: open-jpa-dev@incubator.apache.org Subject: Re: possible to write a JPA Query to that filters both an Entity and its relationship entities? Hi Patrick, From the JPQL select dept, oldtimers from Department dept LEFT JOIN dept.employeeCollection oldtimers WHERE dept.deptno >= 100 AND oldtimers.yearsOfService >= 15 I expect to get SQL that looks something like select dept.id, dept.name, oldtimers.id, oldtimers.firstname, oldtimers.lastname, oldtimers.salary, oldtimers.ssn from Department dept, Employee oldtimers WHERE dept.id = oldtimers.deptid AND dept.deptno >= 100 ANDoldtimers.yearsOfService >= 15 I then construct instances from the returned dept and oldtimerscolumns and give back to the user the results, with one result row foreach SQL ResultSet row. So the filtering from the JPQL translated intothe WHERE clause in the SQL should exclude oldtimers that don't qualify. If you don't use the oldtimers.yearsOfService >= 15 in the SQL, then you will get all of the employees in the department returned in the result. But why do you not use the oldtimers.yearsOfService >= 15 in the SQL? Craig On Feb 23, 2007, at 2:12 PM, Patrick Linskey wrote:In fact, you have to do a bit of work to get SQL to return you non-filtered instances. So I don't get it. Does OpenJPA not construct the obvious SQL that filters oldtimers?I don't think that you and I are really in sync here. Maybesome moreconcrete examples are in order? -Patrick -- Patrick Linskey BEA Systems, Inc.______________________________________________________________ _________ Notice: This email message, together with any attachments, may contain information of BEA Systems, Inc., its subsidiaries and affiliated entities, that may be confidential, proprietary, copyrighted and/or legally privileged, and is intended solely for the use of the individual or entity named in this message. If you are not the intended recipient, and have received this message in error, please immediately return this by email and then delete it.-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Friday, February 23, 2007 2:09 PM To: open-jpa-dev@incubator.apache.org Subject: Re: possible to write a JPA Query to that filters both an Entity and its relationship entities? So, I can tell you that having a result column that is filtered in the query is not what a user would expect. In JDO, the oldtimers columnwould be filtered. In fact, you have to do a bit of work to get SQL to return you non-filtered instances. So I don't get it. Does OpenJPA not construct the obvious SQL that filters oldtimers? I've re-read the JPA specification, and it appears to be silent on the issue of filtering. Is this a portability issue? Craig On Feb 23, 2007, at 1:57 PM, Tom Mutdosch wrote:Hi Patrick, Thanks for the query suggestion. I guess what I was initially thinking of doing was incorrect in that JPA doesn't really give mea "view" of what I want. That is, I can never get a Department object containing a list of filtered Employees. A JPA object returned from a query is always going to be an exactrepresentationof the database. So your Department object is always going to contain all of the Employees in its relationship. So like you mentioned, I can still get all the information using one query, and then just process those results as I want them. I imagine that this would entail some sort of wrapper beanthat wouldhouse the Department and the filtered list of Employees. Or what if I added a regular method to my Department entity called getFilterEmployees() which would return a List that I populated with the filtered results from my query? Does that seem like a reasonable thing to do -- if I didn't want to deal with a wrapper object but still have all of my desired data captured by a single Entity? Thanks Tom Patrick Linskey wrote:It is, but it doesn't buy you much in this situation --the oldTimerscollection in your example won't be filtered to just theones thatare old. It'll be all the employees in the dept. -PatrickCraig Russell Architect, Sun Java Enterprise Systemhttp://java.sun.com/products/jdo 408 276-5638 mailto:[EMAIL PROTECTED] P.S. A good JDO? O, Gasp!Craig RussellArchitect, Sun Java Enterprise System http://java.sun.com/products/ jdo408 276-5638 mailto:[EMAIL PROTECTED] P.S. A good JDO? O, Gasp!
Craig Russell Architect, Sun Java Enterprise System http://java.sun.com/products/jdo 408 276-5638 mailto:[EMAIL PROTECTED] P.S. A good JDO? O, Gasp!
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