I use EclipseLink JPA and for my work. And use GenerationType.TABLE.
When I create a new object using persist, how do I retrieve the id field of the created object.
Example:
em.getTransaction().begin();
Student student = new Student();
student.setName("Joe");
em.persist(student);
em.flush();
em.getTransaction().commit();
Query query = em.createQuery("SELECT e FROM Student e");
List<Student> list = (List<Student>) query.getResultList();
System.out.println(list);
em.close();
emf.close();
So I see all the students, but how do you know which one is the one that I created in an environment where there is competition.
Thanks in advance
I assume question is about generated id, because otherwise you of course already have id in your hands.
Generated id can be found after flush operation with following:
calling student.nameOfTheGetterForID
via PersistenceUnitUtil.getIdentifier:
//cast result to the type of id
em.getEntityManagerFactory().getPersistenceUnitUtil().getIdentifier(student);
Related
I have a User entity generated in Netbeans from an existing database table. The table has a column lastUpdatedByUser that is a User entity. Most of the tables in this database have a lastUpdatedByUser column and queries against those entities correctly return a user object as part of the result.
Ex. Retrieve FROM ProductionTable WHERE date = 'someDate' has a lastUpdatedByUser object that shows who last updated the table row and the rest of their user attributes.
If the productionTable data is edited in the web-app and submitted I need to update the lastUpdatedByUser column.
Users userUpdating = usersService.selectUserEntityByUserId(userId);
Users userEntity = usersFacade.findSingleWithNamedQuery("Users.findByUserId", parameters);
SELECT u FROM Users u WHERE u.userId = :userId
returns a User object that contains a lastUpdatedByUser that is a User object that contains a lastUpdatedByUser that is a User object that contains a lastUpdatedByUser object.... (I have no clue how many there are, and twenty rows of these adds up)
After I persist this
productionEntity.setLastUpdatedByUser(userUpdating);
I get Json StackOverflowError in the next request for the updated entity
gson.toJson(updatedProductionEntity)
The Users entity definition:
#OneToMany(mappedBy = "lastUpdatedByUser")
private Collection<Users> usersCollection;
#JoinColumn(name = "LastUpdatedByUser", referencedColumnName = "UserId")
#ManyToOne
private Users lastUpdatedByUser;
#OneToMany(mappedBy = "lastUpdatedByUser")
private Collection<Production> productionCollection;
How can edit that such that I continue to get a user object as part of other entities like Production, but only a single lastUpdatedByUser object for a User entity?
Thanks for any insight.
I'm guessing this is my issue:
#JoinColumn(name = "LastUpdatedByUser", referencedColumnName = "UserId")
as I found a FK in the Users table to its own UserId
Love refactoring
================================
Drop that FK from the Users table and regenerate the entity in Netbeans and I get
private Integer lastUpdatedByUser;
like it should be
instead of
private Users lastUpdatedByUser;
Now I get to edit all the entities that have valid FKs into the Users table and code and...
Thanks for listening.
I realize this must be a relatively simple thing to do, but I'm not getting what I'm looking for with Google.
I need to get the record ID of the record I just saved using the Entity Framework. With SQL queries we used "Select ##IDENTITY as 'Identity';"
If anyone can help it would be greatly appreciated.
The default behavior of Entity Framework is it sets identity fields on entities from the database right after SaveChanges is called.
In the following sample code, before SaveChanges is called, my employee has a default ID of 0. After SaveChanges my employee has a generated ID of 1.
using (TestDbEntities context = new TestDbEntities())
{
Employee e = new Employee ();
e.FirstName = "John";
e.LastName = "Doe";
context.Employee.Add(e);
context.SaveChanges();
Console.WriteLine("Generated ID: {0}", e.ID);
Console.ReadKey();
}
I have a REST interface for a datamodel that has several one-to-many and many-to-many relationships between entities. While many-to-many relationships seem easy to manage statelessly, I'm having trouble with one-to-many. Consider the following one-to-many relationship:
Employee:
#ManyToOne
#JoinColumn(name = "Company_id")
private Company company;
Company:
#OneToMany(mappedBy = "company", cascade = CascadeType.ALL, orphanRemoval=true)
public Set<Employee> employees = new HashSet<Employee>();
When a company is updated, its employee collection may have been updated as well (employees removed or added) but since the REST interface only allows updating the company as a whole, I cannot explicitly delete or add employees.
Simply replacing the collection does not work, but I found that this seems to work:
public void setEmployees(Set<Employee> employee) {
this.employees.clear(); // magic happens here?
this.employees.addAll(employees);
for (Iterator<Employee> iterator = employees.iterator(); iterator.hasNext();) {
Employee employee = (Employee) iterator.next();
employee.setCompany(this);
}
}
Is this the way it should be done, or is there a better way?
EDIT: In fact the above does not work! It appears to work at first, but then it will break with:
Exception in thread "main" java.lang.IllegalStateException: An entity copy was already assigned to a different entity.
I assume this happens because the db already contains a set of employees and if any of the "old" employees are also part of the replacement set, they collide with the ones in the database.
So what is the right way to replace the set?
First make sure equals is implemented properly. As per hibernate spec: http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html/ch04.html#persistent-classes-equalshashcode
I had a similar problem doing a merge. Essentially I had to fetch the existing employees associated with the company. I had to merge any changes to existing employees, and then add any new employees.
Query query = em.createQuery("select e from Employee e where e.company = '" + company.getId() + "'");
Collection<Employee> existingEmployees = new LinkedList<Employee>();
try{
Iterables.addAll(existingEmployees, (Collection<Employee>) query.getResultList());
}
catch(NoResultException nre){
//No results
}
for(Employee existingEmployee : existingEmployees){
for(Employee employee : company.getEmployees()){
if(existingEmployee.name().equals(employee.name())){
employee.setId(existingEmployee.getId());
}
employee.setCompany(company);
}
}
i think you have no better choice then to replace the existing collection and simply set the new one provided by the REST response.
I have two entities: parent Customer and child Order.
Each Customer has 1,000,000 Orders for example, so it is not needed in any given time to load a Customer with all Orders but I want to have this ability to make join query on these two entities in JPA.
So because of this, I must create #OneToMany relationship for making join queries.
My question is: how to get query without making joinColumn because even in Lazy mode it is possible to load 1,000,000 objects!
I just want to get query on these object with where restrictions like native join.
If you don't want the #OneToMany relationship implicitly set in your Customer class than you don't have to. You can execute JPQL queries (in very precise manner) without the marked relationship.
Assume you have:
#Entity
public class Customer {
// all Customer-related fields WITHOUT #OneToMany relationship with Order
}
#Entity
public class Order {
#ManyToOne
private Customer owner;
}
Then if you want to get all Orders for particular Customer you can execute a simple JPQL query like that:
// Customer customer = ...
// EntityManager em = ...
String jpql = "SELECT o FROM Order o WHERE o.owner = :customer";
TypedQuery<Order> query = em.createQuery(jpql, Order.class);
query.setParameter("customer", customer);
List<Order> orders = query.getResultList();
In this way you can execute the code only when you're really sure you want to fetch Customer's orders.
I hope I've understood your problem correctly.
EclipseLink has support for QueryKeys, that allow you to define fields or relationships for querying that are not mapped. Currently there in no annotation support for query keys, but you can define them using the API and a DescriptorCustomizer.
Also you do not need the OneToMany to query on it, just use the inverse ManyToOne to query,
i.e.
Select distinct c from Customer c, Order o where o.customer = c and o.item = :item
Or,
Select distinct o.customer from Order o join o.customer c where o.customer = c and o.item = :item
I am using DB first method, EF 4.1 with DbContext POCO code gen.
My database has a many-to-many relationship as shown below:
Employee
EmployeeId
EmployeeName
Account
AccountId
AccountName
EmployeeAccount
EmployeeId
AccountId
The problem occurs when I am trying to insert a new Employee, and assign them a pre existing account, so I am basically doing this as below:
Employee emp = new Employee();
emp.EmployeeName = "Test";
emp.Accounts.Add(MethodThatLooksUpAccountByName("SomeAccountName"));
context.Employees.Add(emp);
context.SaveChanges();
The SQL this is executing (incorrectly), is attempting to INSERT a new [Account] record, and this is failing on a constraint violation. Of course, it should not INSERT a new [Account] record, it should only insert a new [EmployeeAccount] record, after inserting the [Employee].
Any advice? Thanks.
MethodThatLooksUpAccountByName does this method return an attached or detached object? In any case, you may try to attach the object it returns to the context.
Employee emp = new Employee();
emp.EmployeeName = "Test";
var acc = MethodThatLooksUpAccountByName("SomeAccountName");
context.Attach(acc); //I don't remember if it's attach or attachobject, but intellisense should help you there.
emp.Accounts.Add(acc);
context.Employees.Add(emp);
context.SaveChanges();