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From my understanding, when an object gets unmarshalled by Jackson, non-mentioned fields in the request call will be set to default value (null if an object), and if there is a constraint on that specific field, say @NotNull, validation fails. Hence partial updates won't be possible.

Does anyone know what is the best workaround for this (partial updates in REST)? Has anyone implemented such thing before?

My hunch is, a merge on the original object (from db) and the new unmarshalled object must occur, and then the object should get validated, but really have no clue how to implement this. Any other ideas would be appreciated.

I'm using Spring 3.1.2 and Jackson 1.9.7.

Peymankh
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1 Answers1

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You could merge yourself the unmarshalled object with the existing one in database, using introspection.

import java.beans.Introspector;
...

Class<?> entityClass = YourEntity.class

// oldEntity is from database
oldEntity = entityManager.getReference(entityclass, id);

for (PropertyDescriptor property : Introspector.getBeanInfo(entityClass).getPropertyDescriptors()) {
    if (property.getReadMethod() != null && property.getWriteMethod() != null) {

        // You retrieve the value of the current property of your unmarshalled entity
        Object newValue = property.getReadMethod().invoke(unmarshalledEntity);

        if (value != null) {
            property.getWriteMethod().invoke(oldEntity, newValue);
        }
    }
}

But with this solution, you cannot update a field to null... It can be a problem. And this is just an idea, you should take care of the type of value, it may be another bean, so you have to introspect recursively your data.

jlabedo
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  • Is it possible to combine this using Jackson and @Valid annotation? Meaning, get the original object from the database before or after unmarshalling the newEntity object and then validating the merged object? – Peymankh Oct 14 '12 at 20:32
  • That doesn't quite answer my question, but for the merging part you are right! – Peymankh Oct 14 '12 at 21:17