JPA Cascading removal of parent and Child - jpa-2.0

Question

I'm trying to learn and understand JPA, and just have a couple of questions regarding deleting a parent and its children in one go. I'm using OpenJPA and EJB3. I have two entities, a Category and a Product. A Category contains many products and a product has a reference to its parent category. The category's list of products is set to cascade.
//Category
#Entity #NamedQueries({#NamedQuery(name = "Category.getCategoryByName", query = "SELECT c FROM Category c WHERE c.name = :name"),#NamedQuery(name = "Category.getCategoryByCategoryId", query = "SELECT c FROM Category c WHERE c.categoryid = :categoryid"), #NamedQuery(name = "Category.getAllCategories", query = "SELECT c FROM Category c left join fetch c.products")})
public class Category implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy=IDENTITY)
private Integer categoryid;
private String name;
//bi-directional many-to-one association to Product
#OneToMany(cascade={CascadeType.ALL}, orphanRemoval = true,
fetch = EAGER, mappedBy="category")
private List<Product> products;
}
//Product
#Entity
#NamedQueries({#NamedQuery(name = "Product.getProductsByCategory",
query = "SELECT p.code, p.description, p.name, p.productid, p.weight FROM Product p WHERE p.category.categoryid = :category_categoryid"),
#NamedQuery(name = "Product.getProductByName", query = "SELECT p FROM Product p WHERE p.name = :name"),
#NamedQuery(name = "Product.getProductByCode", query = "SELECT p FROM Product p WHERE p.code = :code"),
#NamedQuery(name = "Product.getProductByProductId", query = "SELECT p FROM Product p WHERE p.productid = :productid"),
#NamedQuery(name = "Product.getAllProducts", query = "SELECT p FROM Product p")})
public class Product implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy=IDENTITY)
private Integer productid;
private String code;
private String description;
private String name;
private Double weight;
//bi-directional many-to-one association to Category
#ManyToOne(optional = false)
#JoinColumn(name="CATEGORYID")
private Category category;
}
}
// The EJB
#Stateless
#LocalBean
public class ShopManagerBean implements Serializable {
#PersistenceContext(unitName = "TestEJBProject2", type = PersistenceContextType.TRANSACTION)
private EntityManager entityManager;
#TransactionAttribute(TransactionAttributeType.REQUIRED)
public void deleteCategory(Category category)
throws TestApplicationException {
try {
Category actualCat = entityManager.find(Category.class,
category.getCategoryid());
List<Product> products = actualCat.getProducts();
if (products != null) {
Iterator<Product> it = products.iterator();
while (it.hasNext()) {
Product p = it.next();
it.remove();
entityManager.remove(p);
}
}
entityManager.refresh(actualCat);
entityManager.remove(actualCat);
} catch (Exception e) {
e.printStackTrace();
throw new TestApplicationException("Error creating new Product", e);
}
}
}
If I use the following code in the deleteCategory method the EJB then I cannot delete the parent and children as I get an Optimistic Locking exception (An optimistic lock violation was detected when flushing object instance "entity.Product-101" to the data store. This indicates that the object was concurrently modified in another transaction.) - complaining about flushing the product child to the data store
Category actualCat = entityManager.find(Category.class, category.getCategoryid());
if (products != null) {
actualCat.getProducts().clear();
}
entityManager.remove(actualCat);
However, if I use the following code in the deleteCategory method then I can delete the parent and children...but only if I call entityManager.refresh(actualCat) after removing the children and before removing the parent (otherwise I get an optimistic locking exception). Could somebody please explain to me why this is the case and also what the correct/best way of doing a cascading delete with OpenJPA V2 would be?
Category actualCat = entityManager.find(Category.class, category.getCategoryid());
List<Product> products = actualCat.getProducts();
if (products != null) {
Iterator<Product> it = products.iterator();
while (it.hasNext()) {
Product p = it.next();
it.remove();
entityManager.remove(p);
}
}
entityManager.refresh(actualCat);
entityManager.remove(actualCat);
Thanks in advance for your help
Fais
Addition
Here is the db creation script:
--
CREATE SCHEMA "DB2ADMIN";
CREATE TABLE "DB2ADMIN"."CATEGORY" (
"CATEGORYID" INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY ( START WITH 1 INCREMENT BY 1 MINVALUE 1 MAXVALUE 2147483647 NO CYCLE CACHE 20),
"NAME" VARCHAR(50) NOT NULL
)
DATA CAPTURE NONE;
CREATE TABLE "DB2ADMIN"."PRODUCT" (
"PRODUCTID" INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY ( START WITH 1 INCREMENT BY 1 MINVALUE 1 MAXVALUE 2147483647 NO CYCLE CACHE 20),
"CODE" CHAR(15) NOT NULL,
"NAME" VARCHAR(50) NOT NULL,
"DESCRIPTION" VARCHAR(200) NOT NULL,
"WEIGHT" FLOAT(53) NOT NULL,
"CATEGORYID" INTEGER NOT NULL
)
DATA CAPTURE NONE;
ALTER TABLE "DB2ADMIN"."CATEGORY" ADD CONSTRAINT "CATEGORY_PK" PRIMARY KEY
("CATEGORYID");
ALTER TABLE "DB2ADMIN"."PRODUCT" ADD CONSTRAINT "PRODUCT_PK" PRIMARY KEY
("PRODUCTID");
ALTER TABLE "DB2ADMIN"."PRODUCT" ADD CONSTRAINT "PRODUCT_CATEGORY_FK" FOREIGN KEY
("CATEGORYID")
REFERENCES "DB2ADMIN"."CATEGORY"
("CATEGORYID")
ON DELETE CASCADE;