Hi Andy,
This is a good initiative, thank you.
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.
Many users told me it is quite difficult to define fetch plans from independent
fetch groups configured in various classes (and possibly various JDO files).
They would like a way to execute a query with a fetch plan defined next to the
query, by APIs, or by configuration.
Just my 2 cents.
Rgds,
....: Eric Samson, Founder & CTO, Xcalia
Service your Data!
-----Message d'origine-----
De : Andy Jefferson [mailto:[EMAIL PROTECTED]
Envoyé : mardi 13 novembre 2007 11:33
À : [email protected]; JDO Expert Group
Objet : JDO2.1/2.2 Proposal : Dynamic Fetch Groups
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)"
--
Andy (Java Persistent Objects - http://www.jpox.org)
