如何在Microstream中正确使用BinaryHandler来存储易失性的长整型数组？

Question

我试图用Microstream存储Eclipse Collection的LongArrayList (https://www.eclipse.org/collections/)，但由于它的"items“字段是临时的，所以无法开箱即用。

所以我所做的就是创建一个新的类PersistableLongArrayList，如下所示：

public class PersistableLongArrayList extends LongArrayList {
    static BinaryTypeHandler<PersistableLongArrayList> provideTypeHandler() {
        return Binary.TypeHandler(PersistableLongArrayList.class,
            Binary.Field_int(
                "size", 
                list -> list.size, 
                (list, value) -> list.size = value
            ),
            Binary.Field(
                long[].class, "items", 
                list -> list.items, 
                (list, value) -> list.items = value
            )
        );
    } 
}

当从存储实例加载时，items字段现在不为空，但是，如果我后来更改了该值并调用storage.store(list)，关闭数据库并重新启动它，则不会存储新值，只有大小会正确存储。

我添加了一个非常简单的示例来说明此行为：

public class SimpleTest {
    private PersistableLongArrayList root;

    public static void main(String[] args) {
        try {
            SimpleTest t = new SimpleTest();
            // DB erstellen
            EmbeddedStorageManager storage = t.startDB();
            // modify the list
            t.root.add(t.root.size() + 1);
            storage.store(t.root);
            // stop DB
            t.stopDB(storage);
            // restart DB
            storage = t.startDB();
            // show root element
            System.out.println(t.root);
            // Observed behavior: list "grows" from s.th. like this: [1] to s.th. like this [1, 0, 0, 0] after several runs (Probably only size grows and is stored correctly and therefore the fields up to "size" are printed but empty)
            // Expected beahvior: list starts with [1] and grows to something like this [1, 2, 3, 4] after several runs
        } catch (Throwable t) {
            t.printStackTrace();
        } finally {
            System.exit(0);
        }
    }

    private EmbeddedStorageManager startDB() {
        EmbeddedStorageManager storageManager = EmbeddedStorage.start();
        if(storageManager.root() == null) {
            PersistableLongArrayList list = new PersistableLongArrayList();
            storageManager.setRoot(list);
            storageManager.storeRoot();
            root = list;
        } else {
            root = (PersistableLongArrayList)storageManager.root();
        }
        return storageManager;
    }

    private void stopDB(EmbeddedStorageManager storageManager) {
        storageManager.shutdown();
    }
}

可能我只是误解了如何正确使用自定义BinaryHandler，但我现在不知道要更改什么。任何建议都是值得感谢的:)

致以良好的问候，托马斯

Answer 1

使用自定义的PersistenceEagerStoringFieldEvaluator和PersistenceFieldEvaluator，可以直接持久化LongArrayList：

public 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 == org.eclipse.collections.impl.list.mutable.primitive.LongArrayList.class && field.getName().equals("items")) {
            return true;
        }

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

public class PersistenceEagerStoringFieldEvaluatorCustom implements PersistenceEagerStoringFieldEvaluator {

    @Override
    public boolean isEagerStoring(final Class<?> t, final Field u) {

        //return true if field should be persisted at every store
        if(t == org.eclipse.collections.impl.list.mutable.primitive.LongArrayList.class && u.getName().equals("items")) {
            return true;
        }
        return false;
    }
}

设置：

final EmbeddedStorageManager s = EmbeddedStorage.Foundation()
                .onConnectionFoundation(
                        c->{ c.setFieldEvaluatorPersistable(new PersistenceFieldEvaluatorCustom());
                             c.setReferenceFieldEagerEvaluator(new PersistenceEagerStoringFieldEvaluatorCustom());
                        })
                .start();

诚挚的问候

有关更多细节，请参阅https://github.com/microstream-one/microstream/discussions/247