java ee - Can EntityManager be used only within transaction? -


It's obvious that as far as not mentioned, but I still feel the need to confirm it . code EntityManager always has to be in the transaction if it is used for continuous use?

The following application-managed EntityManager does not enter the code until I attach it to the getTransaction (). and getTransaction (). Commit () : 

  EntityManager em = entityManagerFactory .createEntityManager (); Event E = New Event ("One Name", New Date ()); em.persist (e);   
 but  find ()  orientation works fine.  
     
  1.  Does this mean that I can not use EM for writing / updating operations unless that is within the transaction? If that's the case why no exception was thrown when I tried to use it without the transaction? If EM is not within the transaction, can EM be set up to automatically start and transaction?  
  2.  In the case of Container Managed EM, in the context of the same EM example, the various components injected within a transaction are part of 1 transaction in transactions or in many EM examples?  
  3.  Can 1Em example be used in many transactions?