Hi Pinaki, On Oct 31, 2007, at 8:55 PM, Pinaki Poddar wrote:
Hi Craig, I value your observation that we should be careful in using threeterms: 'accessed', 'loaded' and 'fetched' in this context. Let me statemy (limited or even inaccurate) understanding of these terms:accessed : a field f is accessed when user application attempts to getits value for a managed instance X.
ok
loaded: a field f is loaded in X if the value for the field is considered to be the same as that of the datastore.
I'd prefer to consider a field loaded after it's been fetched from the datastore. The issue with using loaded in our discussion is that "load fetch group" loses its context.
fetched: a field f is fetched when its value is read from datastore and set to the instance XYou may correct the above by my following statements are based on theabove understanding.Activating a fetch group doesn't do anything.A more accurate statement would be "execution of a query or find() operation with a fetch configuration that includes fetch group named "f4f5".This is wrong. Only one SQL should be issued, to fetch a specific instance.I beg to differ on qualifying it as 'wrong'. Number of SQL issued to meet a user contract can not be mandated. Trying to issue only one SQL in this case within current implementaion/data structure strategy perhaps will lead to us to a solution similar ro what Teresa outlines.
Ok, but I'd say a key design decision is to limit the number of SQL statements issued in order to retrieve fields from a single instance to exactly one.
I should have underlined that everything is hollow as a pre- condition. I agree that if f3 is pre-loaded then this must not result in fetching f4So this isn't exactly a good example, because it matters whether p1 (the instance of PObject) is already loaded into memory or not.and f5 from datastore.
Here's where I think we are having a problem. If p1 is hollow, then one SQL statement is all you should need to fetch the non- relationship fields. The current fetch plan will result in fetching f1, f2, and f3. If you get these fields and then decide to go back and get f4 and f5, it's wrong. It's not acceptable to go to the datastore to fetch fields and then after you get them, to go back and get more because of a "load fetch group" analysis.
Craig
Pinaki Poddar 972.834.2865-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 31, 2007 10:02 PM To: [email protected] Subject: Re: [jira] Commented: (OPENJPA-370) LoadFetchGroup annotation was not recognized during the fetch1 Hi Pinaki, On Oct 31, 2007, at 6:19 PM, Pinaki Poddar wrote:The implementation is ensuring that the user instance is loaded with requisite fields that can be specified by A) fetch configuration B) fields that are directly accessed C) fields that are included because they are member of a load-fetch-group of another field which is being fetched/accessed.Not exactly. Accessed, yes. Fetched, no. This distinction is critical to understanding how load fetch groups are supposed to work.For concreteness, let us consider the following @Entity public class PObject { @Id private long id; private Integer f2; @LoadFetchGroup("f4f5") private Integer f3; private Integer f4; private Integer f5; Where FetchGroup "f4f5" consists of (you guessed it right:) {"f4", "f5"}. Consider f3 being accessed either by direct load such as Pobject.getF3() or activating a FetchGroup {"f3"}.Activating a fetch group doesn't do anything. Going to the back end to fetch instances causes the fetch plan to be analyzed and fetch groups to actually make something happen. So this isn't exactly a good example, because it matters whether p1 (the instance of PObject) is already loaded into memory or not. So if you em.find(PObject.class, 1) then the current fetch plan is analyzed and if f3 is not in it, then f3 isn't fetched. Full stop.The resultant PObject instance with f1,f2 unloaded and f3,f4,f5 loaded. However, this will result in two separate SQL being issued. SELECT t0.id, t0.f3 FROM pobject t0 SELECT t0.f4, t0.f5 FROM pobject t0 WHERE t0.id = ?This is wrong. Only one SQL should be issued, to fetch a specific instance.The first SQL is resulted because f3 is included in current fecth configuration while f4 and f5 are not.If this is the case, then you should stop here. The load fetch group for f3 must be ignored.The second SQL is resulted of StateManagerImpl.load() thatdetects f3has a fetch group "f4f5". It is part of the current fecthsession andnot a result of post-fetch analysis.Here's where the trouble is. If f3 is not part of the fetch plan, then it should not be fetched.However the way it is done is by adding "f4f5" to the active fetch configuration temporarilyand goingthrough similar cycle that caused the first SQL.This should only occur if p1 is loaded, f3 is not loaded, and f3 is accessed.The concern is I am observing via few test cases this mechanics working to fulfill the user contract. However, Teresa/Kevin reported/observed that LoadFetchGroup is not working. Further investigation on this failure is required before introducing alternative solution.So we need to look at the test cases to validate them before we "fix" anything. CraigRegards -- Pinaki Poddar 972.834.2865-----Original Message----- From: Craig Russell (JIRA) [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 31, 2007 6:52 PM To: [email protected] Subject: [jira] Commented: (OPENJPA-370) LoadFetchGroup annotation was not recognized during the fetch1 [ https://issues.apache.org/jira/browse/OPENJPA-370?page=com.atla ssian.jira.plugin.system.issuetabpanels:comment-tabpanel#action _12539221 ] Craig Russell commented on OPENJPA-370: ---------------------------------------Before the instance is returned to the caller, the fieldsare checked again if they cause any other field be loaded because LoadFecthGroup. At that point, if field f has aLoadFetchGroup L andL is not part of the active fetch configuration then *temporarily* add L to the active FetchConfiguration and go for another 'fetch' (i.e. from the datastore). This sounds wrong. The effect of the load fetch groupshould be partof the fetch strategy, and no post-fetch analysis should bedone. Theonly time the load fetch group is used is if a field f is accessed and it's not already fetched. The intent of the load fetch group is to augment the fetchplan underwhich the persistent instance was fetched. It's designed to provide an intelligent fetch strategy for the lower-usage cases where some use needs field f1 (not in any fetch group in the currentfetch plan)and when using field f1 you want to also fetch fields f2,f3, and f4,that are also not part of the current fetch plan.LoadFetchGroup annotation was not recognized during the fetch1 -------------------------------------------------------------- Key: OPENJPA-370 URL:https://issues.apache.org/jira/browse/OPENJPA-370Project: OpenJPA Issue Type: Bug Components: kernel Affects Versions: 1.0.1, 1.1.0 Reporter: Teresa Kan Assignee: Teresa Kan Fix For: 1.0.1, 1.1.0 Attachments: OPENJPA_370_2.patch, TestFetchGroup.zip Employee class has a LoadFetchGroup annotation defined onthe Rating field, when getRating was called, the address should be returned also. However, openjpa did not handle the LoadFetchGroup correctly, therefore, address was not eargly fetched.public class FGEmployee{ @Id private int id; @OneToOne(fetch=FetchType.LAZY) private FGAddress address; @Basic(fetch=FetchType.LAZY) @LoadFetchGroup("AddressFetchGroup") private String rating; @ManyToOne(fetch=FetchType.LAZY) private FGManager manager; .. }-- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.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 intendedsolely for theuse of the individual or entity named in this message. Ifyou are notthe intended recipient, and have received this message in error, please immediately return this by email and then delete it.Craig RussellArchitect, Sun Java Enterprise System http://java.sun.com/products/ jdo408 276-5638 mailto:[EMAIL PROTECTED] P.S. A good JDO? O, Gasp!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.
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!
smime.p7s
Description: S/MIME cryptographic signature
