Java MongoDB对象版本控制

Question

我需要对存储在面向文档的数据库（MongoDB）中的（简单）Java对象图进行版本控制。对于关系数据库和Hibernate，我发现了Envers，并且对这种可能性感到非常惊奇。Spring
Data Documents是否可以使用类似的东西？

我发现这篇文章概述了我（以及更多…）关于存储对象版本的想法，并且我当前的实现方式与之相似，因为它将对象的副本存储在带有时间戳的单独的历史记录集中，但是我想改善这一点以节省存储空间。因此，我认为我需要同时对对象树执行“
diff”操作和对旧对象进行重构的“ merge”操作。那里有图书馆对此提供帮助吗？

编辑 ：非常感谢与MongoDB和版本控制有关的任何经验！我看到很可能不会有Spring Data解决方案。

Answer 1

我们使用的是基本实体（我们在其中设置ID，创建+上次更改日期，…）。在此基础上，我们使用通用的持久性方法，该方法如下所示：

@Override
public <E extends BaseEntity> ObjectId persist(E entity) {
    delta(entity);
    mongoDataStore.save(entity);
    return entity.getId();
}

delta方法如下所示（我将尝试使其尽可能通用）：

protected <E extends BaseEntity> void delta(E newEntity) {

    // If the entity is null or has no ID, it hasn't been persisted before,
    // so there's no delta to calculate
    if ((newEntity == null) || (newEntity.getId() == null)) {
        return;
    }

    // Get the original entity
    @SuppressWarnings("unchecked")
    E oldEntity = (E) mongoDataStore.get(newEntity.getClass(), newEntity.getId());

    // Ensure that the old entity isn't null
    if (oldEntity == null) {
        LOG.error("Tried to compare and persist null objects - this is not allowed");
        return;
    }

    // Get the current user and ensure it is not null
    String email = ...;

    // Calculate the difference
    // We need to fetch the fields from the parent entity as well as they
    // are not automatically fetched
    Field[] fields = ArrayUtils.addAll(newEntity.getClass().getDeclaredFields(),
            BaseEntity.class.getDeclaredFields());
    Object oldField = null;
    Object newField = null;
    StringBuilder delta = new StringBuilder();
    for (Field field : fields) {
        field.setAccessible(true); // We need to access private fields
        try {
            oldField = field.get(oldEntity);
            newField = field.get(newEntity);
        } catch (IllegalArgumentException e) {
            LOG.error("Bad argument given");
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            LOG.error("Could not access the argument");
            e.printStackTrace();
        }
        if ((oldField != newField)
                && (((oldField != null) && !oldField.equals(newField)) || ((newField != null) && !newField
                        .equals(oldField)))) {
            delta.append(field.getName()).append(": [").append(oldField).append("] -> [")
                    .append(newField).append("]  ");
        }
    }

    // Persist the difference
    if (delta.length() == 0) {
        LOG.warn("The delta is empty - this should not happen");
    } else {
        DeltaEntity deltaEntity = new DeltaEntity(oldEntity.getClass().toString(),
                oldEntity.getId(), oldEntity.getUuid(), email, delta.toString());
        mongoDataStore.save(deltaEntity);
    }
    return;
}

我们的delta实体看起来像这样（没有getters + setters，toString，hashCode和equals）：

@Entity(value = "delta", noClassnameStored = true)
public final class DeltaEntity extends BaseEntity {
    private static final long serialVersionUID = -2770175650780701908L;

    private String entityClass; // Do not call this className as Morphia will
                            // try to work some magic on this automatically
    private ObjectId entityId;
    private String entityUuid;
    private String userEmail;
    private String delta;

    public DeltaEntity() {
        super();
    }

    public DeltaEntity(final String entityClass, final ObjectId entityId, final String entityUuid,
            final String userEmail, final String delta) {
        this();
        this.entityClass = entityClass;
        this.entityId = entityId;
        this.entityUuid = entityUuid;
        this.userEmail = userEmail;
        this.delta = delta;
    }

希望这可以帮助您入门:-)