如何使用CriteriaQuery中

Question

试图采取这种方法，并优化性能选择抽象服务的通用对象列表：

public T getByPrimaryKey(PK id) { 
    T entity = getEntityManager().find(getEntityClass(), id); 
    if(entity != null) { 
     preProcessEntity(entity); 
    } 
    fireEvent(entity, IEntityEventService.Event.READ, null); 
    return entity; 
} 

的原因是，我们有我们得到基于本地ID列表许多领域查询，并且它们正在逐个处理，导致由Hibernate创建的单个查询。我想让Hibernate一次抓取这些。

public List<T> getEntitiesByPrimaryKey(List<PK> pks) { 
    CriteriaBuilder cb = getEntityManager().getCriteriaBuilder(); 
    CriteriaQuery<T> cq = cb.createQuery(getEntityClass()); 
    Root<T> root = cq.from(getEntityClass()); 

    Metamodel m = getEntityManager().getMetamodel(); 
    EntityType<T> T_ = m.entity(getEntityClass()); 

    Path<T> keyPath = root.get(T_.getDeclaredId(getEntityClass())); 
    cq.select(root); 
    cq.where(keyPath.in(pks)); 

    List<T> entities = getEntityManager().createQuery(cq).getResultList(); 
    if(entities != null) { 
     for (T entity : entities) { 
      preProcessEntity(entity); 
      fireEvent(entity, IEntityEventService.Event.READ, null); 
     } 
    } 
    return entities; 
} 

我不知道该从哪里出发。主键不保证是整数，但几乎肯定会是。

Answer 1

下面是固定的：

//grabs the primaryKeyClass from generic type argument list (this was AbstractService<PK, T>) 
    @SuppressWarnings("unchecked") 
    protected Class<PK> primaryKeyClass = (Class<PK>) GenericTypeResolver.resolveTypeArguments(getClass(), AbstractService.class)[0]; 

    protected Class<PK> getPrimaryKeyClass() { 
     return primaryKeyClass; 
    } 

    //code to retrieve generic list based on primary key 
    public List<T> getEntitiesByPrimaryKey(List<PK> pks) { 
     if(pks == null || pks.size() == 0) 
      return new ArrayList<T>(); 

     CriteriaBuilder cb = getEntityManager().getCriteriaBuilder(); 
     CriteriaQuery<T> cq = cb.createQuery(getEntityClass()); 
     Root<T> root = cq.from(getEntityClass()); 

     Metamodel m = getEntityManager().getMetamodel(); 
     EntityType<T> T_ = m.entity(getEntityClass()); 
     Path<PK> keyPath = root.get(T_.getId(getPrimaryKeyClass())); 

     cq.select(root); 
     cq.where(keyPath.in(pks)); 

     List<T> entities = getEntityManager().createQuery(cq).getResultList(); 
     if(entities != null) { 
      for (T entity : entities) { 
       preProcessEntity(entity); 
       fireEvent(entity, IEntityEventService.Event.READ, null); 
      } 
     } 
     return entities; 
    }