Is there a way to find out the
java.lang.Class
that is the one having
#Entity(name = "X")?
In other words use the Entity Name to get the classname of the Entity, of course at runtime :)
All registered #Entitys are available by MetaModel#getEntities(). It returns a List<EntityType<?>> whereby the EntityType has a getName() method representing the #Entity(name) and a getJavaType() representing the associated #Entity class. The MetaModel instance is in turn available by EntityManager#getMetaModel().
In other words, here's the approach in flavor of an utility method:
public static Class<?> getEntityClass(EntityManager entityManager, String entityName) {
for (EntityType<?> entity : entityManager.getMetamodel().getEntities()) {
if (entityName.equals(entity.getName())) {
return entity.getJavaType();
}
}
return null;
}
I've raised an issue in the JPA spec to be able to load entity by entity name 4 years ago and still no development on the matter:
https://github.com/javaee/jpa-spec/issues/85
Related
How can I know if a class is annotated with javax.persistence.Entity?
Person (Entity)
#Entity
#Table(name = "t_person")
public class Person {
...
}
PersonManager
#Stateless
public class PersonManager {
#PersistenceContext
protected EntityManager em;
public Person findById(int id) {
Person person = this.em.find(Person.class, id);
return person;
}
I try to do it with instance of as the following
#Inject
PersonManager manager;
Object o = manager.findById(1);
o instanceof Entity // false
however the result is false, shouldn't it be true?
While the existing answers provide a (somehow) working solution, some things should be noted:
Using an approach based on Reflection implies (a) Performance Overhead and (b) Security Restrictions (see Drawbacks of Reflection).
Using an ORM-specific (here: Hibernate) approach risks portability of the code towards other execution environments, i.e., application containers or other customer-related settings.
Luckily, there is a third JPA-only way of detecting whether a certain Java class (type) is a (managed) #Entity. This approach makes use of standardized access to the javax.persistence.metamodel.MetaModel. With it you get the method
Set < EntityType > getEntities();
It only lists types annotated with #Entity AND which are detected by the current instance of EntityManager you use. With every object of EntityType it is possible to call
Class< ? > getJavaType();
For demonstration purposes, I quickly wrote a method which requires an instance of EntityManager (here: em), either injected or created ad-hoc:
private boolean isEntity(Class<?> clazz) {
boolean foundEntity = false;
Set<EntityType<?>> entities = em.getMetamodel().getEntities();
for(EntityType<?> entityType :entities) {
Class<?> entityClass = entityType.getJavaType();
if(entityClass.equals(clazz)) {
foundEntity = true;
}
}
return foundEntity;
}
You can provide such a method (either public or protected) in a central place (such as a Service class) for easy re-use by your application components. The above example shall just give a direction of what to look for aiming at a pure JPA approach.
For reference see sections 5.1.1 (page 218) and 5.1.2 (page 219f) of the JPA 2.1 specification.
Hope it helps.
If the statement
sessionFactory.getClassMetadata( HibernateProxyHelper.getClassWithoutInitializingProxy( Person.class ) ) != null;
is true, than it is an entity.
#NiVer's answer is valid. But, if you don't have a session or sessionFactory at that point you could use Reflection. Something like:
o.getClass().getAnnotation(Entity.class) != null;
I have a JPA entity, with its attibutes and several NamedQueries.
I'm trying to log some information "any time the entity is used for something", i.e.:
any time any of its NamedQueries is invoked
any time the entity is used in a Query q = em.createQuery("SELECT....FROM thisEntity a, otherEntity b WHERE.....");
any time any of its attributes is accessed
The information i want to log must include the invoker class name and invoker method, among other.
I guess this must be achieved through interceptors, but i'm not sure for example if interceptors allow me to intercept the accesses to the class throw its NamedQueries.
You could achieve that using callback methods like #PrePersist, #PostPersist, #PostLoad, #PreUpdate, #PostUpdate, #PreRemove, #PostRemove inside the entity classes.
For example
public class EntityA {
...
#PrePersist
public void beforePersist(){
//Log information
}
}
Additionally you could use that callback methods in listener classes.
public class EntityListenerA{
#PrePersist
public void beforePersist(EntityA ob) {
//Log information
}
}
#EntityListeners(EntityListenerA.class)
public class EntityA {
...
}
In your case I supose you must use the callback #PostLoad depending on the query.
Hope this help
Is it possible to add summary properties(no database column) according LINQ from another property(column) in EF generated class from database and this property don't update(delete or remove from class) when update model from database(because this property(cloumn) is not on database)
Yes, it is. Classed generated by Entity Framework as an Entitied are always marked partial. It lets you extend the functionality with your own properties or method.
Let say your entity class is named Post. You can extend it with code like that:
public partial class Post
{
public int Average
{
get
{
return this.Items.Average();
}
}
}
Because it's not a part of designer-generated file it won't be overwritten when it's regenerated. However, there is one requirement to make it work: your custom part of Post class has to be in exactly the same namespace as code generated by EF.
Try using the [NotMapped] attribute on a property in a partial class. This will be ignored by Entity Framework.
public partial class EntityName
{
[NotMapped]
public int CalculatedProperty
{
get
{
return Numbers.Sum();
}
}
}
I'd like to know how to create a method that will allow me to generically do this...
public class Repo<T> : IGenericRepo<T> where T : class
{
protected PteDotNetEntities db;
public T Get(int id)
{
//how do I dynamically get to the correct entity object and select it by
//id?
}
}
Yes you can. If you know that all your entities will have simple primary key property of type int and name Id you can do simply this:
public interface IEntity
{
int Id { get; }
}
All your entities must implement this interface. Next you can simply do:
public class Repo<T> : IGenericRepo<T> where T : class, IEntity
{
protected PteDotNetEntities db;
public T Get(int id)
{
return db.CreateObjectSet<T>().FirstOrDefault(e => e.Id == id);
}
}
This is the simplest possible solution. There are better solutions using GetObjectByKey but they are more complex. The difference between FirstOrDefault and GetObjectByKey is repeatable execution. FirstOrDefault always executes DB query whereas GetObjectByKey first checks if the entity with the same key was already loaded / attached to the context and returns it without querying the database. As reference for version using GetObjectByKey you can check similar questions:
Entity Framework Simple Generic GetByID but has differents PK Name
Generic GetById for complex PK
You can simplify those examples if you know the name of the key property upfront (forced by the interface).
In case of using code first / DbContext API you can also check this question:
Generic repository EF4 CTP5 getById
Error: The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.
I am trying to create a WCF service with Entity Framework (VS 2010, .NET 4). When I run it, I get the above error.
I read something about editing the T4 template, but it appears that it already has
[DataContractAttribute(IsReference=true)]
public partial class Person : EntityObject
and
[DataMemberAttribute()]
public global::System.Int32 ID
{
get
{
return _ID;
}
I am not sure what the difference is between
[DataMemberAttribute()] and [DataMember]
or
[DataContractAttribute(IsReference=true)] and [DataContract]
either.
public Person GetPersonByID(int id)
{
using (var ctx = new MyEntities())
{
return (from p in ctx.Person
where p.ID == id
select p).FirstOrDefault();
}
}
How does WCF and EF work together, properly?
Do you have navigation properties in your Person class? Did you disable lazy loading? Otherwise it will probably try to load content for navigation properties during serialization and it fails because of closed context.
To your other questions:
[DataMemberAttribute()] and [DataMember] are same. It is just shorter name.
[DataContractAttribute(IsReference=true)] and [DataContract] are not same. IsRefrence allows tracking circular references in navigation properties. Without this parameter circular reference causes never ending recursion.