eclipselink + @convert(json) + postgres + list property

Question

I'm using eclipselink 2.6 as a persistence provider of spring data jpa, that in my understanding, now allows you to serialize a subtree of an entity as json using the internal moxy serializer.

So I'm trying to mix this to migrate from embedded element collections to a serialized json using the json datatype of postgres. I have an entity named Product, and this entity have the following mapped property:

@Convert(Convert.JSON) 
private List<MetadataIndex> indexes=new ArrayList<MetadataIndex> ();

In which metadata index is a simple class with a few string properties. I would like to convert this list of object into a json and store it into a column of json data type in postgres.

I thought that the above code should suffice, but it does not. The application crashes on boot (can't create entitymanager factory - npe somwhere inside eclipselink).

If I change the converter to @Convert(Convert.SERIALIZED) it works. It creates a field on the table Products named indexes of type bytea and store the serialized list in it. Is this an eclipselink bug or I'm missing something?

Thank you.

yes. But not with this method. I'll post the full code as the answer in a few minutes. — fer.marino, Jul 02 '15 at 06:50

score 4 · Answer 1 · answered Jul 02 '15 at 13:55

well, I've used a custom eclipselink converter to convert my classes into json objects, then store them into the db using directly the postgres driver. This is the converter.

import fr.gael.dhus.database.jpa.domain.MetadataIndex;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.type.TypeReference;
import org.eclipse.persistence.mappings.DatabaseMapping;
import org.eclipse.persistence.sessions.Session;
import org.postgresql.util.PGobject;

import javax.persistence.AttributeConverter;
import javax.persistence.Converter;
import java.io.IOException;
import java.sql.SQLException;
import java.util.Collection;
import java.util.List;

/**
 * Created by fmarino on 20/03/2015.
 */
@Converter
public class JsonConverter implements org.eclipse.persistence.mappings.converters.Converter {

    private static ObjectMapper mapper =  new ObjectMapper();

    @Override
    public Object convertObjectValueToDataValue(Object objectValue, Session session) {
        try {
            PGobject out = new PGobject();
            out.setType("jsonb");
            out.setValue( mapper.writerWithType( new TypeReference<Collection<MetadataIndex>>() {} )
                    .writeValueAsString(objectValue) );
            return out;
        } catch (IOException e) {
            throw new IllegalArgumentException("Unable to serialize to json field ", e);
        } catch (SQLException e) {
            throw new IllegalArgumentException("Unable to serialize to json field ", e);
        }
    }

    @Override
    public Object convertDataValueToObjectValue(Object dataValue, Session session) {
        try {
            if(dataValue instanceof PGobject && ((PGobject) dataValue).getType().equals("jsonb"))
                return mapper.reader( new TypeReference<Collection<MetadataIndex>>() {}).readValue(((PGobject) dataValue).getValue());
            return "-";
        } catch (IOException e) {
            throw new IllegalArgumentException("Unable to deserialize to json field ", e);
        }
    }

    @Override
    public boolean isMutable() {
        return false;
    }

    @Override
    public void initialize(DatabaseMapping mapping, Session session) {

    }

}

as you can see I use jackson for serialization, and specify the datatype as Collection. You can use the type you want here.

Inside my classes, I've mapped my field with this:

@Convert(converter = JsonConverter.class)
@Column (nullable = true, columnDefinition = "jsonb")

adding also this annotation to the class:

@Converter(converterClass = JsonConverter.class, name = "jsonConverter")

To make things works properly with jackson I've also added to my MetadataIndex class this annotation, on the class element:

@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.PROPERTY, property = "@class")

I personally like using directly the postgres driver to store those kind of special datatype. I didn't manage to achieve the same with hibernate. As for the converter, I've would preferred a more general solution, but jackson forced me to state the object type I want to convert. If you find a better way to do it, let me know.

With a similar approach, I've also manage to use the hstore datatype of postgres.

Thanks for the answer, How to handle convertDataValueToObjectValue(), If the Metadata is of abstract class and I have 2 other classes(Eg: MetadataA, MetadataB) which extends Metadata class. I am unable to deserialize from json to collection in this situation. — Pavan Sokke Nagaraj, Oct 03 '16 at 13:30
this is more related to how jackson deal with deserialization. See http://stackoverflow.com/questions/16800896/java-unmarshilling-json-data-containg-abstract-type — fer.marino, Oct 04 '16 at 07:14
Yup, I realized it later. Thanks a lot. Could you just share how can I achieve the same with Hstore. THanks — Pavan Sokke Nagaraj, Oct 04 '16 at 14:56
How to handle the mapping exception when Collection is null? — Pavan Sokke Nagaraj, Nov 02 '16 at 21:35

eclipselink + @convert(json) + postgres + list property

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