Saving a POJO in MongoDB with null fields using Jongo - mongodb

Question

so I have a POJO object that I am creating and saving to a MongoDB collection using Jongo:
import java.util.Map;
public class MyObject {
private String name;
private Map<String, String> mappings;
public MyObject() {
}
public MyObject(String name, Map mappings) {
this.name = name;
this.mappings = mappings;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Map<String, String> getMappings() {
return mappings;
}
public void setMappings(Map<String, String> mappings) {
this.mappings = mappings;
}
}
Test class for saving objects to mongo:
import com.mongodb.DB;
import com.mongodb.MongoClient;
import org.jongo.Jongo;
import org.jongo.MongoCollection;
import java.net.UnknownHostException;
import java.util.HashMap;
public class NullFieldTest {
public static void main(String[] args) throws UnknownHostException {
DB db = new MongoClient("localhost", 27017).getDB("testDB") ;
Jongo jongo = new Jongo(db);
MongoCollection testCollection = jongo.getCollection("testCollection");
MyObject objectA = new MyObject("objectA", new HashMap());
MyObject objectB = new MyObject("objectB", null);
testCollection.save(objectA);
testCollection.save(objectB);
}
}
This test saves the objects fine:
{
"_id" : ObjectId("543cf1a6cd8936deafcf66cf"),
"name" : "objectA",
"mappings" : {}
}
{
"_id" : ObjectId("543cf1a6cd8936deafcf66d0"),
"name" : "objectB"
}
but what I really want is for the null mappings in objectB to appear as
"mappings" : null
I know that a field within a collection can have a null value, but I dont know how to do this with the jongo driver, any ideas?
FYI, I'm using jongo V1.1

Answer 1

problem solved, my issue was in the serialization of the objects, added an annotation from Jackson to include even null fields:
#JsonInclude(JsonInclude.Include.ALWAYS)
public class MyObject {
Found more details on this post:
How to tell Jackson to ignore a field during serialization if its value is null?

Answer 2

Jongo comes with a pre-configured Jackson which ignore null fields : https://github.com/bguerout/jongo/blob/443b461e47acdcffb9f51efafb291b7e0c805c26/src/main/java/org/jongo/marshall/jackson/configuration/VisibilityModifier.java
You can change this configuration by creating a custom Mapper using JacksonMapper.Builder :
Mapper mapper = new JacksonMapper.Builder().addModifier(new MapperModifier() {
public void modify(ObjectMapper mapper) {
mapper.setSerializationInclusion(JsonInclude.Include.ALWAYS);
}
}).build();
Jongo jongo = new Jongo(db, mapper);