Currently a new instance of EntityManagerFactory will be created each
time this method is called. A fair amount of the work related to
creating an EntityManagerFactory, however, only needs to occur the first
time an EntityManagerFactory is created for a persistence unit.
-Tom
Marina Vatkina wrote:
>Tom,
>
>Calling Persistence.createEntityManagerFactory(pu) is accessing PU outside
>a container. Will this call create a new EMF every time?
>
>thanks,
>-marina
>
>Tom Ware wrote:
>
>
>>Hi Marcel,
>>
>> I'll handle question #2. I'll let the folks that work on the container
>>answer the other ones.
>>
>>#2 The javaagent is used to allow us to do dynamic weaving of domain
>>classes that use fetch=LAZY for OneToOne and ManyToOne mappings. Those
>>classes are weaved to contain som TopLink-specific data structures that
>>allow us to provide LAZY loading of those relationships. If you do not
>>want to (or cannot use the agent), a flag can be provided in the
>>properties of your persitence unit to avoid the weaving. The property
>>"toplink.weaving" can be set to "false". This will disable the
>>weaving. The consequences of setting this property is that the LAZY
>>hint will not be observed for OneToOne and ManyToOne relationships and
>>they will be loaded EAGERly.
>>
>>-Tom
>>
>>Marcel Overdijk wrote:
>>
>>
>>
>>>Hi,
>>>
>>>I'm adding JPA support to a framework and have some questions.
>>>Currently I'm using the Toplink Essentials and javaee.jar from
>>>GlassFish M6.
>>>
>>>1. The javaee.jar contains more then only the persistence related
>>>classes and therefor is 1mb big. Is there a official Sun jar
>>>downloadable containing only persistence classes. In Spring 2.0
>>>distribution a persistence.jar (58kb) is included. I can use this but
>>>I don't know the origin of it.
>>>
>>>2. In the persistence example on the GlassFish page the
>>>toplinks-essentials-agent.jar is used in combination with -javaagent
>>>(SE example). What does the toplink-essentials-agent do? If I just put
>>>toplink-essentials and javaee.jar on the classpath everything seems to
>>>work fine. Is there any drawback?
>>>
>>>3. When I want to get an EntityManager based on an persistence unit
>>>Name I don't know at compile time. The only option (I believe) is to
>>>create an emf first:
>>>String pu = "some dynamic pu name";
>>>Persistence.createEntityManagerFactory(pu);
>>>However to create a emf each time is expensive. I could keep a
>>>reference to a pu once created.
>>>But what I'm wondering is how JEE 5 containers handle this. Do they
>>>create subsequent emf's or are they smart that they know it was
>>>already created in a previous call?
>>>
>>>Hope you can hekp me on this.
>>>
>>>Regards,
>>>Marcel Overdijk
>>>
>>>
>>>
>>>
>>>