Serialization of Guava collections

[fedordar]

Hello,
are guava collections compatible with microstream? to be more specific, I ran into a problem when using ImmutableList, which has a field of objects inside, designated transient. I tried to create a PersistenceFieldEvaluator that would persist all fields (including transient). But when i reloaded the saved object, this array returns null elements. Is it possible to resolve this issue in another way?

[hg-ms]

Hello,
it should be possible to get the Guava ImmutableList persisted. Using a custom PersistenceFieldEvaluator is a suitable approach. One thing you must consider is that there are several implementations of the abstract ImmutableList. The example below handles the RegularImmutableList and SingletonImmutableList implementations.

Why your PersistenceFieldEvaluator did not work is hard to say, did you delete the storage after adding the PersistenceFieldEvaluator to ensure that there is no old data (that has the transient array not peristed)?

One other tip: You can have a look in the PersistenceTypeDictionary.ptd file in the storage directory to identify all persisted classes and the fields they persisted.

package one.microstream;

import com.google.common.collect.ImmutableList;
import one.microstream.persistence.types.PersistenceFieldEvaluator;
import one.microstream.reflect.XReflect;
import one.microstream.storage.embedded.types.EmbeddedStorage;
import one.microstream.storage.embedded.types.EmbeddedStorageManager;

import java.lang.reflect.Field;

public class Main {

    public static void main(String[] args) {

        System.out.println("Persisting Guava ImmutableList");

        try (EmbeddedStorageManager storageManager = EmbeddedStorage
                .Foundation().onConnectionFoundation(
                        cf -> cf.setFieldEvaluatorPersistable(new PersistenceFieldEvaluatorCustom())).start()) {

            if (storageManager.root() == null) {
                ImmutableList<String> immutableList = ImmutableList.of("Hello, World");
                storageManager.setRoot(immutableList);
                storageManager.storeRoot();

                System.out.println("created new storage with root: " + immutableList);

            } else {
                ImmutableList<String> immutableList = (ImmutableList<String>) storageManager.root();
                System.out.println("loaded existing storage with root: " + immutableList);
            }
        }
    }

    public static class PersistenceFieldEvaluatorCustom implements PersistenceFieldEvaluator {

        @Override
        public boolean applies(final Class<?> entityType, final Field field) {

            //return true if field should be persisted, false if not
            if (entityType.getName().equals("com.google.common.collect.RegularImmutableList") && field.getName().equals("array")) {
                return true;
            }
            if (entityType.getName().equals("com.google.common.collect.SingletonImmutableList") && field.getName().equals("element")) {
                return true;
            }

            //default: return false if field has the transient modifier
            return !XReflect.isTransient(field);
        }
    }
}

[fedordar]

Thank you for your answer!