Return Objects Here are the rules for defining return types for the select method:. Entity Beans. Paul Anilprem. The EJB specification details how an application server provides the following responsibilities:. The container performs the database manipulations—insertion, deletion, and updating the data records—because it is aware of the relationship of the database fields and the corresponding Entity bean data objects. That is, no explicit configuration is needed. If you would like a reply to your comment, please submit your email address: Note: We may not respond to all submitted comments.
JDO 2. In addition, many vendors will likely implement JDO 2.
The two main objectives of the JDO architecture, which is shown in Figure 1, are to provide Java application developers a transparent Java technology-centric view of persistent information and to enable pluggable implementations of data stores into application servers. It is important to note that JDO does not define the type of data store: You can use the same interface to persist your Java technology objects to a relational database, an object database, XML, or any data store.
They are complementary approaches with unique strengths, and developers with different skill sets and different development objectives can use either. For example, JDBC offers developers greater flexibility by giving them direct control over database access and cache management. JDBC is a more mature technology with wide industry acceptance. This frees Java platform developers to focus on the DOM without necessarily knowing or having to learn SQL, while JDO takes care of the details of the field-by-field storage of objects in a persistent store.
In response, Sun Microsystems is leading a community effort to create a single POJO persistence model for the Java technology community.
Members of the JDO 2. The EJB 3. The language has been updated to work better with EJB 3. JDO manages the life cycle of an object from creation to deletion.
The transition between states is achieved using methods of the PersistenceManager class including the TransactionManager -- such as makePersistent , makeTransient , deletePersistent -- and committing or rolling back changes that such operations make. Table 1 shows the 10 states defined by the JDO specification. The first seven states are required, and the last three are optional. If an implementation does not support certain operations, then the three optional states are not reachable.
Special Edition Using Enterprise JavaBeans [Chuck Cavaness, Brian Keeton] on cydyqywyty.cf *FREE* shipping on qualifying offers. Special Edition Using. From the Publisher: Special Edition Using EJB starts with a description of how EJB fits into the big picture of J2EE development, then covers such topics as.
No JDO identity is associated with a transient instance. Persistent-new Any object that has been requested by the application component to become persistent using the makePersistent method of the PersistenceManager class. Such an object will have an assigned JDO identity. Persistent-dirty Any persistent object that was changed in the current transaction. Hollow Any persistent object that represents specific data in the data store but whose values are not in the instance. Persistent-clean Any persistent object that represents specific transactional data in the data store and whose values have not been changed in the current transaction.
Persistent-deleted Any persistent object that represents specific data in the data store and that has been deleted in the current transaction. Persistent-new-deleted Any persistent object that has been made newly persistent and deleted in the same transaction. Persistent-nontransactional Any persistent object that represents data in the data store, whose values are currently loaded but not transactionally consistent Transient-client Any persistent object that represents a transient transactional instance whose values have not been changed in the current transaction.
Transient-dirty Any persistent object that represents a transient transaction instance whose values have been changed in the current transaction. The snippets of code later in this article demonstrate how to perform some of the operations we have just discussed.
The JDO reference implementation , which is available from Sun Microsystems, comes with a file-based storage mechanism called fstore. JDO 1. But due to timing constraints, the JDO 2. Several commercial implementations are available.
Once a PersistenceManager is obtained, an application can perform tasks such as making an object persistent, retrieving an object from persistence, deleting an object from persistence, updating an object, and so on. The following snippet of code shows how to make an object persistent. It updates the state of the object from Transient to Hollow :. Retrieving an object from persistence is equally simple: You can use Extent a holder for information or Query which provides more accurate filtering.
Here is an example using Extent :.
Finally, deleting an object from persistence can be done simply by first retrieving the object from persistence as shown earlier and then invoking the deletePersistent obj method. The JDO specification requires that vendors provide a query capability using JDOQL, which is a query language oriented around the objects that are persisted. The PersistenceManager class defines methods for constructing instances of Query -instance implementation classes. Description Table of Contents Product Details Click on the cover image above to read some pages of this book!
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