10 | JPA Query Structure (JPQL / Criteria) is that SQL works with relational database tables, records and fields, whereas JPQL works with Java ... rather than just field values from database tables, as with SQL. That makes JPQL more object oriented friendly ... JPQL Query The following query retrieves all the Country objects in the database: SELECT c FROM |
10 | Updating JPA Entity ObjectsModifying existing entity objects that are stored in the database is based on transparent ... Once an entity object is retrieved from the database (no matter which way) it can simply be modified in memory ... (); The entity object is physically updated in the database when the transaction is committed |
9 | Is ObjectDB scalable? What are its limitations?ObjectDB is highly scalable and can manage efficiently databases in a wide range of sizes, from ... supports: Database file size up to 128 TB (= 131,072 GB = 134,217,728 MB). Up to 2,147,483,648 entity classes per database file. Up to 2,147,483,648 indexes per database file |
9 | What is the Java Persistence API (JPA)?The Java Persistence API (JPA) is a standard API for accessing databases from within Java applications. The main advantage of JPA over JDBC (the older Java API for interacting with databases ... . Using plain old Java objects (POJO) to represent persistent data can significantly simplify database |
9 | Deleting JPA Entity ObjectsExisting entity objects can be deleted from the database either explicitly by invoking the remove ... from the database it has to first be retrieved (no matter which way) and then in an active ... (); The entity object is physically deleted from the database when the transaction is committed. Embedded |
8 | JPA Lifecycle Events (added to the EntityManager). @PostPersist - after storing a new entity in the database (during commit or flush). @PostLoad - after an entity has been retrieved from the database. @PreUpdate ... the database (during commit or flush). @PreRemove - when an entity is marked for removal in |
1 | Step 4: Add a Servlet Class response) throws ServletException, IOException { // Obtain a database connection ... , response); } finally { // Close the database connection: if (em ... (representing a database connection) is constructed. If a new guest has registered (using a JSP form |
1 | Step 4: Add a Servlet Class, IOException { // Obtain a database connection: EntityManagerFactory emf ... { // Close the database connection: if (em.getTransaction().isActive ... the application scope attribute, and then an EntityManager (representing a database connection |
1 | Step 3: Define an EJB Session BeanOperations on the database will be performed by an instance of a session bean (EJB) class ... class GuestDao { // Injected database connection: @PersistenceContext private EntityManager ... two methods: persist - for storing a new Guest entity object in the database. getAllGuests |
0 | Which API should I use - JPA or JDO? code. When to prefer JDO JDO might be preferred when portability to other object databases is more important than general portability to both object and relational databases. JPA is designated to be used mainly with relational databases. ObjectDB is the only object database that supports JPA |
