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Spring JPA - Best way to update multiple fields

I'm new to using JPA and trying to transition my code from JdbcTemplate to JPA. Originally I updated a subset of my columns by taking in a map of the columns with their values and created the SQL Update string myself and executed it using a DAO. I was wondering what would be the best way to do something similar using JPA?
EDIT:
How would I transform this code from my DAO to something equivalent in JPA?
public void updateFields(String userId, Map<String, String> fields) {
StringBuilder sb = new StringBuilder();
for (Entry<String, String> entry : fields.entrySet()) {
sb.append(entry.getKey());
sb.append("='");
sb.append(StringEscapeUtils.escapeEcmaScript(entry.getValue()));
sb.append("', ");
}
String str = sb.toString();
if (str.length() > 2) {
str = str.substring(0, str.length() - 2); // remove ", "
String sql = "UPDATE users_table SET " + str + " WHERE user_id=?";
jdbcTemplate.update(sql, new Object[] { userId },
new int[] { Types.VARCHAR });
}
}

You have to read more about JPA for sure :)
Once entity is in Persistence Context it is tracked by JPA provider till the end of persistence context life or until EntityManager#detach() method is called. When transaction finishes (commit) - the state of managed entities in persistence context is synchronized with database and all changes are made.
If your entity is new, you can simply put it in the persistece context by invoking EntityManager#persist() method.
In your case (update of existing entity), you have to get a row from database and somehow change it to entity. It can be done in many ways, but the simpliest is to call EntityManager#find() method which will return managed entity. Returned object will be also put to current persistence context, so if there is an active transaction, you can change whatever property you like (not the primary key) and just finish transaction by invoking commit (or if this is container managed transaction just finish method).
update
After your comment I can see your point. I think you should redesign your app to fit JPA standards and capabilities. Anyway - if you already have a map of pairs <Attribute_name, Attrbute_value>, you can make use of something called Metamodel. Simple usage is shown below. This is naive implementation and works good only with basic attributes, you should take care of relationships etc. (access to more informations about attributes can be done via methods attr.getJavaType() or attr.getPersistentAttributeType())
Metamodel meta = entityManager.getMetamodel();
EntityType<User> user_ = meta.entity(User.class);
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaUpdate<User> update = cb.createCriteriaUpdate(User.class);
Root e = update.from(User.class);
for( Attribute<? super User, ?> attr : user_.getAttributes() ) {
if (map.containsKey(attr.getName())) {
update.set(attr, map.get(attr));
}
}
update.where(cb.equal(e.get("id"), idOfUser));
entityManager.createQuery(update).executeUpdate();
Please note that Update Criteria Queries are available in JPA since 2.1 version.
Here you can find more informations about metamodel generation.
Alternatively to metamodel you can just use java reflection mechanisms.

JPA handles the update. Retrieve a dataset as entity using the entitymanager, change the value and call persist. This will store the changed data in your db.

In case you are using Hibernate(as JPA provider), here's an example
Entity
#Entity
#Table(name="PERSON")
public class Person {
#Id #GeneratedValue(strategy=GenerationType.IDENTITY)
private int id;
#Column(name="NAME", nullable=false)
private String name;
other fields....
}
DAO
public interface PersonDao {
Person findById(int id);
void persist(Person person);
...
}
DaoImpl
#Repository("personDao")
public class PersonDaoImpl extends AnAbstractClassWithSessionFactory implements PersonDao {
public Person findById(int id) {
return (Person) getSession().get(Person.class, id);
}
public void persist(Person person){
getSession().persist(person);
}
}
Service
#Service("personService")
#Transactional
public class PersonServiceImpl implements PersonService {
#Autowired
PersonDao personDao;
#Override
public void createAndPersist(SomeSourceObject object) {
//create Person object and populates with the source object
Person person = new Person();
person.name = object.name;
...
personDao.persist(person);
}
#Override
public Person findById(int id) {
return personDao.findById(id);
}
public void doSomethingWithPerson(Person person) {
person.setName(person.getName()+" HELLO ");
//here since we are in transaction, no need to explicitly call update/merge
//it will be updated in db as soon as the methods completed successfully
//OR
//changes will be undone if transaction failed/rolledback
}
}
JPA documentation are indeed good resource for details.
From design point of view, if you have web interfacing, i tends to say include one more service delegate layer(PersonDelegateService e.g.) which maps the actual data received from UI to person entity (and viceversa, for display, to populate the view object from person entity) and delegate to service for actual person entity processing.

JPA - #PreRemove method behaviour

I have 2 entities with many-to-many relationship. The Movie Entity is the owner of this relation, so when I want to delete an Actor Entity I use a method annotated #PreRemove to delete any occurrences of Actor ID in Movie cast to avoid "Foreign key violation exception".
Movie class
#Entity
public class Movie extends AbstractBusinessObject{
#ManyToMany
private Map<String, Actor> cast;
// setters and getters
public void removeCastMember(Actor actor){
for (Entry<String, Actor> e : cast.entrySet()) {
if(e.getValue().id.equals(actor.id)){
cast.remove(e.getKey());
}
}
} // removeCastMember()
}
Actor class
#Entity
public class Actor extends AbstractBusinessObject{
#ManyToMany(mappedBy = "cast")
private Set<Movie> movies;
// setters and getters
#PreRemove
private void removeActorFromMovies() {
for (Movie m : movies) {
m.removeCastMember(this);
}
}
}
To be clear, from my testing, it works - movie objects are correctly updated in the database. However, I cannot understand how is it possible when there are no calls to saveOrUpdate() or persist/merge those objects.

That's a fundamental feature of JPA/Hibernate. All the changes made to attached entities are automatically made persistent: Hibernate manages them, so it compares their current state with their initial state, and automatically makes all the changes persistent.
This is extremely useful, because you don't have to track all the entities that have been modified in a complex business method modifying lots of entities. And it's also efficient because Hibernate won't execute unnecessary SQL: if an entity hasn't changed during the transaction, no SQL update query will be executed for this entity. And if you modify entities and then throw an exception rollbacking the transaction, Hibernate will skip the updates.
So, typical JPA code would look like this:
void transfer(Long fromAccountId, Long toAccountId, BigDecimal amount) {
Account from = em.find(Account.class, fromAccountId); // from is managed by JPA
Account to = em.find(Account.class, ftoAccountId); // to is managed by JPA
from.remove(amount);
to.add(amount);
// now the transaction ends, Hibernate sees that the state of from and to
// has changed, and it saves the entities automatically before the commit
}
persist() is used to make a new entity persistent, i.e. to make it managed by Hibernate.
merge() is used to take a detached entity (i.e. an entity which is not managed by Hibernate, but already has an ID and a state) and to copy its state to the attached entity having the same ID.

ManyToMany NOT NULL check constraint when using Named query

I have an Entity (Layer) that maps a list of other Entities (Member). This List may have no entries / be null. Yet, when I query for the Entity I get a NOT NULL check constraint error from the database.
It seems to be connected to the NamedQueries as I can read the Entity from DB if I query by id.
#Entity
#NamedQueries({
#NamedQuery(name="getChildLayers",-
query = "SELECT la
FROM Layer la
WHERE la.parent = :parent AND la.deletedDate IS NULL")})
public class Layer extends CommonModel {
/*... other field */
#ManyToOne(fetch = FetchType.LAZY, targetEntity = Layer.class, optional = true)
private Layer parent;
#ManyToMany(fetch = FetchType.LAZY, targetEntity = MyUser.class)
private List<MyUser> members;
public List<MyUser> getMembers() {
return members;
}
public void setMembers(List<MyUser> members) {
this.members = members;
}
/*... other getters and setters */
}
I get this error: integrity constraint violation: NOT NULL check constraint; SYS_CT_10298 table: LAYER_MYUSER column: MEMBERS_ID
I am able to create the entry, though.
When I run my tests then all tests fail that read the Entity (but creation works). If I add the following line in the creation method:
layer.setMembers(new ArrayList<MyUser>());
then the methods that test the alternation of the members work (meaning, I can create a Layer and alter its members by adding and removing elements from the list).
It seems to me that reading the Entity from Database fails whenever there are no Member to the Layer.
I did try adding #JoinColumn(nullable=true) to the field, but it changed nothing.
I import javax.persistence classes.
Example as to how I access the variable (in LayerService)
// this method works as expected
public Layer getById(Long id) {
Session s = sessionFactory.getCurrentSession();
return (Layer)s.get(Layer.class, id);
}
// this does not.
public List<Layer> getChildren(Layer layer) {
Query childrenQuery = sessionFactory.getCurrentSession().getNamedQuery("getChildLayers");
childrenQuery.setParameter("parent", layer);
return (List<Layer>) childrenQuery.list();
}
Code changed after Jason Cs answer:
Layer
...
private final List<OCWUser> members = new ArrayList<>();
...
public void setMembers(List<OCWUser> members) {
this.members.clear();
this.members.addAll(members);
}
Problem still exists.

It can be so simple. I forgot to add #JoinTable
#JoinTable(name = "LAYER_USER", joinColumns = #JoinColumn(nullable = true))

One important thing to be aware of is you shouldn't replace this.members with another list in setMembers unless you know you are doing it before you call persist(). Instead you need to clear this.members then add all the specified elements to it. The reason is that Hibernate can and will use its own proxied / instrumented collections classes when [de]serializing an entity, and you blow that away when overwriting the collection class. You should declare members as final and always initialize it to a non-null empty List.
See for example (3.6 but still relevant): http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html/collections.html#collections-persistent, In particular:
Notice how in Example 7.2, “Collection mapping using #OneToMany and
#JoinColumn” the instance variable parts was initialized with an
instance of HashSet. This is the best way to initialize collection
valued properties of newly instantiated (non-persistent) instances.
When you make the instance persistent, by calling persist(), Hibernate
will actually replace the HashSet with an instance of Hibernate's own
implementation of Set.
As long as you are messing with collection fields in this way, any number of strange things can happen.
Also, in general, you want to be careful about stating your invariants and such when accessing collections in this way, as it's easily possible to, e.g., create two Layers that reference the same collection internally, so that actions on one affect the other, or external actions on the passed-in collection affect the layer, e.g. the following code probably doesn't behave like you want it to:
List<MyUser> u = new ArrayList<MyUser>();
Layer a = new Layer();
Layer b = new Layer();
u.add(...);
a.setMembers(u);
b.setMembers(u);
u.clear();
Further, when you persist() one of the layers there, and Hibernate overwrites the field with its own collection class, the behavior then changes as the objects are no longer referencing the same collection:
// not only did u.clear() [possibly undesirably] affect a and b above, but:
session.persist(a);
u.add(...); // ... now it only affects b.

One-to-many relationship: Update removed children with JPA 2.0

I have a bidirectional one-to-many relationship.
0 or 1 client <-> List of 0 or more product orders.
That relationship should be set or unset on both entities:
On the client side, I want to set the List of product orders assigned to the client; the client should then be set / unset to the orders chosen automatically.
On the product order side, I want to set the client to which the oder is assigned; that product order should then be removed from its previously assiged client's list and added to the new assigned client's list.
I want to use pure JPA 2.0 annotations and one "merge" call to the entity manager only (with cascade options). I've tried with the following code pieces, but it doesn't work (I use EclipseLink 2.2.0 as persistence provider)
#Entity
public class Client implements Serializable {
#OneToMany(mappedBy = "client", cascade= CascadeType.ALL)
private List<ProductOrder> orders = new ArrayList<>();
public void setOrders(List<ProductOrder> orders) {
for (ProductOrder order : this.orders) {
order.unsetClient();
// don't use order.setClient(null);
// (ConcurrentModificationEx on array)
// TODO doesn't work!
}
for (ProductOrder order : orders) {
order.setClient(this);
}
this.orders = orders;
}
// other fields / getters / setters
}
#Entity
public class ProductOrder implements Serializable {
#ManyToOne(cascade= CascadeType.ALL)
private Client client;
public void setClient(Client client) {
// remove from previous client
if (this.client != null) {
this.client.getOrders().remove(this);
}
this.client = client;
// add to new client
if (client != null && !client.getOrders().contains(this)) {
client.getOrders().add(this);
}
}
public void unsetClient() {
client = null;
}
// other fields / getters / setters
}
Facade code for persisting client:
// call setters on entity by JSF frontend...
getEntityManager().merge(client)
Facade code for persisting product order:
// call setters on entity by JSF frontend...
getEntityManager().merge(productOrder)
When changing the client assignment on the order side, it works well: On the client side, the order gets removed from the previous client's list and is added to the new client's list (if re-assigned).
BUT when changing on the client side, I can only add orders (on the order side, assignment to the new client is performed), but it just ignores when I remove orders from the client's list (after saving and refreshing, they are still in the list on the client side, and on the order side, they are also still assigned to the previous client.
Just to clarify, I DO NOT want to use a "delete orphan" option: When removing an order from the list, it should not be deleted from the database, but its client assignment should be updated (that is, to null), as defined in the Client#setOrders method. How can this be archieved?
EDIT: Thanks to the help I received here, I was able to fix this problem. See my solution below:
The client ("One" / "owned" side) stores the orders that have been modified in a temporary field.
#Entity
public class Client implements Serializable, EntityContainer {
#OneToMany(mappedBy = "client", cascade= CascadeType.ALL)
private List<ProductOrder> orders = new ArrayList<>();
#Transient
private List<ProductOrder> modifiedOrders = new ArrayList<>();
public void setOrders(List<ProductOrder> orders) {
if (orders == null) {
orders = new ArrayList<>();
}
modifiedOrders = new ArrayList<>();
for (ProductOrder order : this.orders) {
order.unsetClient();
modifiedOrders.add(order);
// don't use order.setClient(null);
// (ConcurrentModificationEx on array)
}
for (ProductOrder order : orders) {
order.setClient(this);
modifiedOrders.add(order);
}
this.orders = orders;
}
#Override // defined by my EntityContainer interface
public List getContainedEntities() {
return modifiedOrders;
}
On the facade, when persisting, it checks if there are any entities that must be persisted, too. Note that I used an interface to encapsulate this logic as my facade is actually generic.
// call setters on entity by JSF frontend...
getEntityManager().merge(entity);
if (entity instanceof EntityContainer) {
EntityContainer entityContainer = (EntityContainer) entity;
for (Object childEntity : entityContainer.getContainedEntities()) {
getEntityManager().merge(childEntity);
}
}

JPA does not do this and as far as I know there is no JPA implementation that does this either. JPA requires you to manage both sides of the relationship. When only one side of the relationship is updated this is sometimes referred to as "object corruption"
JPA does define an "owning" side in a two-way relationship (for a OneToMany this is the side that does NOT have the mappedBy annotation) which it uses to resolve a conflict when persisting to the database (there is only one representation of this relationship in the database compared to the two in memory so a resolution must be made). This is why changes to the ProductOrder class are realized but not changes to the Client class.
Even with the "owning" relationship you should always update both sides. This often leads people to relying on only updating one side and they get in trouble when they turn on the second-level cache. In JPA the conflicts mentioned above are only resolved when an object is persisted and reloaded from the database. Once the 2nd level cache is turned on that may be several transactions down the road and in the meantime you'll be dealing with a corrupted object.

You have to also merge the Orders that you removed, just merging the Client is not enough.
The issue is that although you are changing the Orders that were removed, you are never sending these orders to the server, and never calling merge on them, so there is no way for you changes to be reflected.
You need to call merge on each Order that you remove. Or process your changes locally, so you don't need to serialize or merge any objects.
EclipseLink does have a bidirectional relationship maintenance feature which may work for you in this case, but it is not part of JPA.

Another possible solution is to add the new property on your ProductOrder, I named it detached in the following examples.
When you want to detach the order from the client you can use a callback on the order itself:
#Entity public class ProductOrder implements Serializable {
/*...*/
//in your case this could probably be #Transient
private boolean detached;
#PreUpdate
public void detachFromClient() {
if(this.detached){
client.getOrders().remove(this);
client=null;
}
}
}
Instead of deleting the orders you want to delete you set detached to true. When you will merge & flush the client, the entity manager will detect the modified order and execute the #PreUpdate callback effectively detaching the order from the client.

Hibernate updating one to many collection when object removed from collection

I have run into a nasty bug with jpa and hibernate. I have a billing class with the following annotation:
#OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER)
#JoinColumn(name="ch1_id", referencedColumnName="id")
private List<BillingItem>billingItems = new ArrayList<BillingItem>();
Now I need to filter deleted items from the collection but cannot use anything but jpa. No hibernate specific annotations allowed. So I wrote a post load function:
#PostLoad
public void postLoad() {
ArrayList<BillingItem>tempItems = new ArrayList<BillingItem>();
Iterator<BillingItem> i = this.billingItems.iterator();
BillingItem item;
while(i.hasNext()) {
item = i.next();
if( item.getStatus().equals("D")) {
tempItems.add(item);
}
}
this.billingItems.removeAll(tempItems);
}
However when there are deleted items to filter I'm seeing
Hibernate: update billing_on_item set ch1_id=null where ch1_id=? and id=?
which produces an exception because ch1_id is a foreign key and cannot be null. However hibernate is binding the parameters to correct values. Why is this update occurring in the first place? How do I correct the error?
Thanks in advance,
Randy

By removing the items from the collection, you're telling Hibernate that the association between the two entities doesn't exist anymore, so obviously, Hibernate removes what materializes this association in the database: it sets the foreign key to null.
What you probably want is just a getter in your entity that returns only the non-deleted items:
public List<BillingItem> getNonDeletedItems() {
List<BillingItem> result = new ArrayList<BillingItem>();
for (BillingItem item : this.billingItems) {
if (!"D".equals(item.getStatus()) {
result.add(item);
}
}
return result;
}

The #OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER) line says that it will cascade ALL updates. Look into CascadeType.