Java JPA：Select'ATTRIBUTE is in List <>'

Question

我正在使用JPA並試圖選擇給定List父母（Category）的所有childentities（Product）。關係是Category OneToMany Product。我想將它保留在一個查詢中，而不是像product.get("category") == category.get(0) || product.get("category") == category.get(1) || ...那樣創建Predicate。

我已經嘗試了下面的代碼，但這似乎不起作用（如在底部的堆棧中所見）。有沒有人有如何完成這一建議？

代碼

public List<Product> findProductsBy(List<Category> categories) { 
    CriteriaBuilder cb = em.getCriteriaBuilder(); 
    CriteriaQuery<Product> query = cb.createQuery(Product.class); 
    Root product = query.from(Product.class); 
    Predicate predicateCategory = product.get("category").in(categories); 

    query.select(product).where(predicateCategory); 
    return em.createQuery(query).getResultList(); 
} 

堆棧

WARNING: Local Exception Stack: 
Exception [EclipseLink-6075] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.QueryException 
Exception Description: Object comparisons can only use the equal() or notEqual() operators. Other comparisons must be done through query keys or direct attribute level comparisons. 
Expression: [ 
Relation operator [ IN ] 
    Query Key category 
     Base (...).Product 

Answer 1

什麼，你可以使用類ID而不是類對象（如錯誤狀態做到：不支持對象比較）：

（假設y我們的類ID是Long，你可以做以下。）

public List<Product> findProductsBy(List<Category> categories) { 
    List<Long> categoryIds = new ArrayList<Long>(); 
    for(Category category:categories){ 
     categoryIds.add(category.getId()); 
    } 
    CriteriaBuilder cb = em.getCriteriaBuilder(); 
    CriteriaQuery<Product> query = cb.createQuery(Product.class); 
    Root product = query.from(Product.class); 
    Predicate predicateCategory = product.get("categoryId").in(categoryIds); 

    query.select(product).where(predicateCategory); 
    return em.createQuery(query).getResultList(); 

}