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https://issues.apache.org/jira/browse/JDO-554?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andy Jefferson updated JDO-554:
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Fix Version/s: JDO 2 maintenance release 2
> JDO2.2 : Dynamic fetch groups
> -----------------------------
>
> Key: JDO-554
> URL: https://issues.apache.org/jira/browse/JDO-554
> Project: JDO
> Issue Type: New Feature
> Components: api2, api2-legacy, specification
> Reporter: Andy Jefferson
> Fix For: JDO 2 maintenance release 2
>
>
> From the Apache JDO jdo-dev mailing list, to register the issue for a
> subsequent JDO release, and holder for any further discussion
> Below is a proposal that could possibly be included in a JDO2.2 (or in JDO2.1
> if feedback is positive for that, and JPOX already implements it).
> ========================================
> Problem : fetch groups are static, defined in metadata (XML/annotations).
> Sometimes it would be more convenient to be able to define fetch groups
> dynamically, for example based on user interaction in a web system.
> ========================================
> Proposal :
> We add a new interface defining a FetchGroup, where a FetchGroup has a
> symbolic name and is for a class defining the fields of that class that are
> in the fetch group.
> public interface FetchGroup
> {
> String getName(); // Symbolic name (as also used in MetaData)
> String getClassName(); // Class to which this group refers
> FetchGroup add(String fieldName); // Add a field
> FetchGroup remove(String fieldName); // Remove a field
> boolean hasField(String fieldName);
> String[] getFieldNames();
> void setPostLoad(boolean postLoad);
> boolean getPostLoad();
> }
> We allow users to register/deregister their FetchGroups with the PMF
> PersistenceManagerFactory
> {
> ...
> void addFetchGroup(FetchGroup grp);
> void removeFetchGroup(String name, Class cls);
> FetchGroup createFetchGroup(String name, Class cls);
> FetchGroup getFetchGroup(String grpName, Class cls);
> FetchGroup[] getFetchGroups();
> void clearFetchGroups();
> }
> ========================================
> Usage:
> FetchGroup grp1 = pmf.createFetchGroup("myGroup1", MyClass.class);
> grp1.add("field1").add("field2").add("field4");
> pmf.addFetchGroup(grp1); // FetchGroup registered
> pm.getFetchPlan().setGroup("myGroup1"); // FetchGroup used in this plan
> // FetchPlan now has MyClass {field1, field2, field4}
> We can then also allow dynamic changes like
> pmf.getFetchGroup("myGroup1", MyClass.class).add("field7");
> and this is directly reflected in the FetchPlan
> Possible changes:-
> 1. PMF has createFetchGroup and addFetchGroup and we could merge these so
> when creating a FetchGroup it is added
> 2. Doesnt support "recursion-depth" specification when adding a field to a
> FetchGroup, so we could add a method "add(String fieldName, int depth)"
> Comments by Erik Samson
> JDO 2 needs alternate ways to define fetch plans. Some food for thoughts here:
> - possibility to add the DFG of a class into a fetch group
> - possibility to add all fields of a class into a fetch group
> - possibility to add all primitive fields of a class into a fetch
> group
> - possibility to add all reference fields of a class into a fetch
> group
> - possibility to add all collections fields of a class into a fetch
> group
> - possibility to remove all primitive fields of a class into a fetch
> group
> - possibility to remove all reference fields of a class into a fetch
> group
> - possibility to remove all collections fields of a class into a
> fetch group
> - possibility to create a global fetch plan without fetch groups at
> all
> pm.setFetchPlan( "Person(name,age, address( {dfg} , country( {all} , -flagIMG
> ) ), accounts( {simple} , +{references} ) )" ) ;
> Person actually references the candidate class, so I suppose it could be
> optional.
> This method will load name and age from a Person, then will load the
> configured DFG from the reference to Address, then will load all fields but
> flagIMG from the reference to Country into address, and finally will load
> simple fields and unary references to other objects from the collection of
> Accounts. We should also probably support depth in that mechanism.
> Having this "SSFP" (Single String Fetch Plan) will allow to tune the system
> externally, from JMX or a configuration file for instance.
> Comments by Matthew Adams
> You might also consider overloaded methods on interface FetchGroup, just for
> completeness:
> // (importing java.lang.reflect.Field)
> FetchGroup add(Field field);
> FetchGroup remove(Field field);
> boolean hasField(Field field); // or has(Field) -- I'd consider better verb
> Field[] getFields();
> The add & remove methods should throw if the Field isn't contained in the
> class.
> Comments by Christiaan:
> May be also think about an option to restore to a fetchGroup to a state
> before you start changing it (possibly via supporting clone()) or reset to
> configuration defined in JDO file.
> Comments by Craig Russell:
> Also, I think that we should consider ways to manipulate FetchPlans as well,
> both in programmatic as well as declarative approaches. Specifically, I'd
> like to be able to specify in my configuration the FetchPlan to use in a
> specific application context, e.g. the first time a PersistenceManager is
> used to getObjectById or newQuery, the FetchPlan for that use case is looked
> up from configuration and set as the current FetchPlan.
> Further, if the application wants a specific FetchPlan, they should be able
> to call a method setFetchPlan with either the name of a configured FetchPlan
> or a FetchPlan to use.
> And then, assuming that the FetchPlan must change during some interval of
> application processing, and then reset to the previous settings,
> public void pushFetchPlan(FetchPlan);
> public void pushFetchPlan(String fetchPlanName)
> public FetchPlan popFetchPlan()
> would allow a temporary override of the FetchPlan without the application
> having to preserve the settings and update the FetchPlan to restore it.
> In this light, it might make sense to be able to register FetchPlans by name
> with the PersistenceManagerFactory.
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