11-13-07 12:11 PM
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 g
roup
· possibility to add all reference fields of a class into a fetch g
roup
· possibility to add all collections fields of a class into a fetch
group
· possibility to remove all primitive fields of a class into a fetc
h group
· possibility to remove all reference fields of a class into a fetc
h group
· possibility to remove all collections fields of a class into a fe
tch 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 opt
ional.
This method will load name and age from a Person, then will load the configu
red 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 fi
elds 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 sys
tem externally, from JMX or a configuration file for instance.
Many users told me it is quite difficult to define fetch plans from independ
ent fetch groups configured in various classes (and possibly various JDO fil
es). 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:andy@jpox.org]
Envoyé : mardi 13 novembre 2007 11:33
À : jdo-dev@db.apache.org; 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 wh
en
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)
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