Probably the exact details of em.flush() are implementation-dependent. In general anyway, JPA providers like Hibernate can cache the SQL instructions they are supposed to send to the database, often until you actually commit the transaction. For example, you call em.persist(), Hibernate remembers it has to make a database INSERT, but does not actually execute the … Read more
A persistence context handles a set of entities which hold data to be persisted in some persistence store (e.g. a database). In particular, the context is aware of the different states an entity can have (e.g. managed, detached) in relation to both the context and the underlying persistence store. Although Hibernate-related (a JPA provider), I … Read more
Sometimes changes made to the model or to the ORM may not reflect accurately on the database even after an execution of SchemaUpdate. If the error actually seems to lack a sensible explanation, try recreating the database (or at least creating a new one) and scaffolding it with SchemaExport.
Put the “hibernate-entitymanager.jar” in the classpath of application. For newer versions, you should use “hibernate-core.jar” instead of the deprecated hibernate-entitymanager If you are running through some IDE, like Eclipse: Project Properties -> Java Build Path -> Libraries. Otherwise put it in the /lib of your application.
Answers are directly available on documentation I realize it can help make my DAOs work with a plain JDO PersistenceManagerFactory. Yes. TransactionAwarePersistenceManagerFactoryProxy proxy allows DAOs to work with a plain JDO PersistenceManagerFactory reference, while still participating in Spring’s (or a J2EE server’s) resource and transaction management. You can surely use it in your app. But … Read more
Here’s my understanding of the methods. Mainly these are based on the API though as I don’t use all of these in practice. saveOrUpdate Calls either save or update depending on some checks. E.g. if no identifier exists, save is called. Otherwise update is called. save Persists an entity. Will assign an identifier if one … Read more
@NotNull is a JSR 303 Bean Validation annotation. It has nothing to do with database constraints itself. As Hibernate is the reference implementation of JSR 303, however, it intelligently picks up on these constraints and translates them into database constraints for you, so you get two for the price of one. @Column(nullable = false) is … Read more
You could use the pickle module in the standard library. Here’s an elementary application of it to your example: import pickle class Company(object): def __init__(self, name, value): self.name = name self.value = value with open(‘company_data.pkl’, ‘wb’) as outp: company1 = Company(‘banana’, 40) pickle.dump(company1, outp, pickle.HIGHEST_PROTOCOL) company2 = Company(‘spam’, 42) pickle.dump(company2, outp, pickle.HIGHEST_PROTOCOL) del company1 del … Read more