JDO, org.json.simple.JSONObject and PostgreSQL JSON type

Question

In my PostgreSQL database I have:

CREATE TABLE category (
    // ...
    category_name_localization JSON not null,
);

In Java, I have a JDO class like so:

@javax.jdo.annotations.PersistenceCapable(table = "category" )
public class Category extends _BlueEntity implements Serializable {
    //...

    private org.json.simple.JSONObject category_name_localization;

    @javax.jdo.annotations.Column( name = "category_name_localization" )
    public org.json.simple.JSONObject getCategoryNameLocalization() {
        return category_name_localization;
    }
}

When I use this class, DataNucleus gives the following exception:

org.datanucleus.exceptions.NucleusUserException: Field "com.advantagegroup.blue.ui.entity.Category.category_name_localization" is a map that has been specified without a join table and neither the key nor the value has a mapped-by specified. This is invalid!
                at org.datanucleus.store.rdbms.RDBMSStoreManager.newJoinTable(RDBMSStoreManager.java:2720)
                at org.datanucleus.store.rdbms.mapping.java.AbstractContainerMapping.initialize(AbstractContainerMapping.java:82)
                at org.datanucleus.store.rdbms.mapping.MappingManagerImpl.getMapping(MappingManagerImpl.java:680)
                at org.datanucleus.store.rdbms.table.ClassTable.manageMembers(ClassTable.java:518)
                at org.datanucleus.store.rdbms.table.ClassTable.manageClass(ClassTable.java:424)
                at org.datanucleus.store.rdbms.table.ClassTable.initializeForClass(ClassTable.java:1250)
                at org.datanucleus.store.rdbms.table.ClassTable.initialize(ClassTable.java:271)
                at org.datanucleus.store.rdbms.RDBMSStoreManager$ClassAdder.initializeClassTables(RDBMSStoreManager.java:3288)
                at org.datanucleus.store.rdbms.RDBMSStoreManager$ClassAdder.run(RDBMSStoreManager.java:2897)
                at org.datanucleus.store.rdbms.AbstractSchemaTransaction.execute(AbstractSchemaTransaction.java:118)
                at org.datanucleus.store.rdbms.RDBMSStoreManager.manageClasses(RDBMSStoreManager.java:1637)
                at org.datanucleus.store.rdbms.RDBMSStoreManager.getDatastoreClass(RDBMSStoreManager.java:665)
                at org.datanucleus.store.rdbms.RDBMSStoreManager.getPropertiesForGenerator(RDBMSStoreManager.java:2098)
                at org.datanucleus.store.AbstractStoreManager.getStrategyValue(AbstractStoreManager.java:1278)
                at org.datanucleus.ExecutionContextImpl.newObjectId(ExecutionContextImpl.java:3668)
                at org.datanucleus.state.StateManagerImpl.setIdentity(StateManagerImpl.java:2276)
                at org.datanucleus.state.StateManagerImpl.initialiseForPersistentNew(StateManagerImpl.java:482)
                at org.datanucleus.state.StateManagerImpl.initialiseForPersistentNew(StateManagerImpl.java:122)
                at org.datanucleus.state.ObjectProviderFactoryImpl.newForPersistentNew(ObjectProviderFactoryImpl.java:218)
                at org.datanucleus.ExecutionContextImpl.persistObjectInternal(ExecutionContextImpl.java:1986)
                at org.datanucleus.ExecutionContextImpl.persistObjectWork(ExecutionContextImpl.java:1830)
                at org.datanucleus.ExecutionContextImpl.persistObject(ExecutionContextImpl.java:1685)
                at org.datanucleus.api.jdo.JDOPersistenceManager.jdoMakePersistent(JDOPersistenceManager.java:712)
                at org.datanucleus.api.jdo.JDOPersistenceManager.makePersistent(JDOPersistenceManager.java:738)
                at com.advantagegroup.blue.ui.jdo._BlueJdo.insert(_BlueJdo.java:40)
                at ...

This error makes sense in a way, because org.json.simple.JSONObject extends Map. However, this field is not part of any relationships -- it is of type JSON and therefore it is natural to back it with JSONObject

How do I tell JDO / DataNucleus to chill and treat org.json.simple.JSONObject the same way it would a String or a Date?

Thanks! DC

Since it is not a recognized type, have you thought of provide a JDO "AttributeConverter" for it ? — Neil Stockton
– Neil Stockton, Commented Mar 10, 2017 at 18:27
I tried that, but even with a converter DataNucleus is still looking for a related table. The problem is not that I can't save the field; the problem is that JDO automatically thinks the fields is part of a many-to-many mapping -- which it is not. I can't figure out how to tell JDO that this field does not map to other classes/tables. — Dave Cherkassky
– Dave Cherkassky, Commented Mar 10, 2017 at 18:56
So post it in your question? and post the stack trace then someone who knows the code can tell you WHY — Neil Stockton
– Neil Stockton, Commented Mar 10, 2017 at 18:59
Ummm I did put that error message in the question. I've updated the pst to include the stack trace for completeness. — Dave Cherkassky
– Dave Cherkassky, Commented Mar 10, 2017 at 19:04
For completeness: if I try to add an AttributeConverter to the field, like so: @Convert( value=JSONConverter.class ) public JSONObject category_name_localization = new JSONObject(); Then during enhancement/ process fails: Nested Throwables StackTrace: java.lang.NullPointerException at java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1011) at java.util.concurrent.ConcurrentHashMap.put(ConcurrentHashMap.java:1006) at org.datanucleus.store.types.TypeManagerImpl.registerConverter(TypeManagerImpl.java:457) at ... — Dave Cherkassky
– Dave Cherkassky, Commented Mar 10, 2017 at 19:54

Neil Stockton · Accepted Answer · 2017-03-11 13:23:50Z

2

My understanding of this is that your default attempt is trying to persist a normal Map (since while it doesnt know what a JSONObject is, it does know what a Map is), and it will need a join table for that for RDBMS.

Since you presumably want the JSONObject persisted into a single column then you need to create a JDO AttributeConverter. I've done similar things with my own types and it works fine (i'm on v5.0.5 IIRC).

I also found this in their docs, for when you have your own Map class that it doesn't know how to handle by default in terms of replacing it with a proxy (to intercept the calls to put, putAll etc). If you add that line it will not try to wrap this field with a proxy (which it doesn't know how to do for that type, unless you tell it). If you wanted to auto-detect the JSONObject becoming "dirty" you would need to write a proxy wrapper, as per this page.

This doesn't answer how to map the column for that converter to use a "json" type in PostgreSQL, but i'd guess that if you set the sqlType you may get success in that respect.

edited Mar 11, 2017 at 13:23

answered Mar 11, 2017 at 9:15

Neil Stockton

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Dave Cherkassky Over a year ago

Implementing a converter alone did not work very well. However, with a wrapper, everything worked perfectly!

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