ObjectDB Database Search

The Java Persistence API (JPA) provides various ways to retrieve objects from the database. The retrieval of objects does not require an active transaction because it does not change the content of the database. The persistence context serves as a cache of retrieved entity objects. If a requested

that it manages. The persistence context serves as a first level cache. An attempt to retrieve ... : On retrieval - shared cache is used for entity objects that are not in the persistence context. If an entity object is not available also in the shared cache - it is retrieved from the database and added

requires using entity objects for many operations, including storing, retrieving , updating and deleting ... are provided in the Storing Entities section. Entity objects retrieved from the database by an EntityManager are also in the Managed state. Object retrieval is discussed in more detail in the Retrieving

require separate space allocation and separate store and retrieval operations. Therefore, using ... has several benefits: It saves space in the database. It is more efficient (storage and retrieval are faster ... map type is used, ObjectDB will switch to a similar supported type when the data is retrieved from

(using another EntityManager ) since it was retrieved by the current updater. Optimistic locking ... retrieval operation or query . Releasing a Pessimistic Lock Pessimistic locks are automatically ... _FORCE_INCREMENT) . Locking during Retrieval JPA 2 provides various methods for locking entity objects

The JPA Metamodel API provides the ability to examine the persistent object model and retrieve ... . Three methods can be used to retrieve sets of types: // Get all the managed classes: // (entity classes ... methods can be used to retrieve a specific type by its Class instance: // Get a managed type (entity

after retrieval by a special automatic query. Note : Navigation through inverse fields is much less efficient ... when a Department entity is retrieved from the database. ObjectDB accomplishes this by effectively running ... Map . For an inverse list field, the order of the retrieved owner entities can be set by the OrderBy

: Retrieving the entity objects into an EntityManager . Removing these objects from the EntityManager   ... , which are used to retrieve data from the database, DELETE queries do not retrieve data from ... from the database using a DELETE query may be slightly more efficient than retrieving entity objects

Existing entity objects can be updated, as explained in chapter 2 , by: Retrieving ... to retrieve data from the database, UPDATE queries do not retrieve data from the database ... the database using an UPDATE query may be slightly more efficient than retrieving entity objects

the database is uniquely identified (and can be retrieved from the database) by the combination of its type ... have to be retrieved by their primary key as shown in the Retrieving Entities section. Embedded Primary Key ... time, sensor ID and additional details. Suppose that queries that retrieve all the events

The ability to retrieve managed entity objects is a major advantage of JPQL. For example ... query retrieves the name of the capital city of a specified country: SELECT c.capital.name FROM ... that are retrieved directly by a result path expression are not associated with an EntityManager and changes

the following INNER JOIN query that retrieves pairs of (country name, capital name): SELECT c.name, p ... , since the referenced  Capital objects are retrieved one at a time, i.e. the number of round trips ... objects because it eliminates the need for retrieving the associated Capital objects separately

query retrieves countries whose population and area (both) exceed specified limits: SELECT c FROM ... The following query retrieves countries whose population or area exceeds a specified limit: SELECT c ... The following query retrieves all the countries whose population does not exceed a specified limit: SELECT

classes and objects. For example, a JPQL query can retrieve and return entity objects ... ...]] [ORDER BY ...] The first two clauses, SELECT and FROM are required in every retrieval query ... Query The following query retrieves all the Country objects in the database: SELECT c FROM Country

JPQL query that retrieves selective objects from the database. Out of the four optional clauses ... The following query retrieves only countries with a population size above a population size p ... them to the SELECT clause. For example, the following query retrieves all the countries with population size

Query Execution (with getResultList) The following query retrieves all the Country objects in ... the country names, a query using projection and retrieving country names directly instead of retrieving the entire Country instances would be more efficient. Single Result Query Execution

: Exceptions can also be thrown on an attempt to retrieve entity objects from the database. For example ... (above) may also be thrown during retrieval , if database lock has been requested for retrieved entity objects and it cannot be granted.

number ( 0 for the first page), the following expression retrieves the results for a specified page ... on all the result objects that the query retrieves . For example, the following query execution sets

Query parameters enable the definition of reusable queries. Such queries can be executed with different parameter values to retrieve different results. Running the same query multiple times ... ) The following method retrieves a Country object from the database by its name: public Country

Once an entity object is retrieved from the database (no matter which way) it can simply be modified in memory ... when it is retrieved from the database and to compare that snapshot to the actual managed object

ObjectDB databases and perform basic CRUD operations (Create/Store, Retrieve , Update and Delete ... storing, retrieving , updating and deleting Point objects. This chapter contains the following sections

- after an entity has been retrieved from the database. @PreUpdate - when an entity is identified as modified by

). Retrieval by navigation from detached objects is not supported, so only persistent fields

whose name is  "Country.findAll" that retrieves all the  Country objects in the database

to enable selective retrieval by type . In JPQL an entity type literal is written simply as the name

  Boost your application database performance. Database performance is critical as it is the bottleneck in most applications. ObjectDB is extremely fast and much faster than any other JPA solution. Using a relational database management system (RDBMS) to store and retrieve Java objects

class, and accordingly, provides the ability to store Point objects in the database and retrieve

ObjectDB is an Object Oriented Database Management System (ODBMS). It provides all the standard database management services (storage and retrieval , transactions, lock management, query processing, etc.), but it uses an object oriented model to store and manage data. You can easily store ordinary

which retrieves all the Country objects in the database is represented by both q1 and q2 . When building

Given an EntityManager , em , that represents a JPA connection to the object database, we can use it to store, retrieve , update and delete database objects. Storing New Entity Objects The following code fragment stores 1,000 Point  objects in the database: em. getTransaction (). begin

ObjectDB. hows how to use JPA to store, retrieve , update and delete database objects. Explains

JDO Method in javax.jdo.PersistenceManager void retrieve (   Object pc,    boolean useFetchPlan ) Retrieve field values of an instance from the store. This tells ... must be retrieved . If the useFetchPlan parameter is false, this method behaves exactly as the corresponding

JDO Method in javax.jdo.PersistenceManager void retrieve (   Object pc ) Retrieve ... intends to use the instance, and its field values must be retrieved . The PersistenceManager might use policy information about the class to retrieve associated instances. Parameters: pc - the instance Since: JDO 1.0

is retrieved from the application scope attribute, and then an EntityManager (representing a database ... entity objects are retrieved from the database and stored in the request's "guest" attribute

: public void persist(Guest guest) { em.persist(guest); } // Retrieves all the guests: public List ... - for retrieving all the existing  Guest objects from the database. EJB classes are only supported by Java EE

void persist(Guest guest) { em.persist(guest); } // Retrieves all the guests: public List getAllGuests ... - for storing a new  Guest entity object in the database. getAllGuests - for retrieving all the existing

void persist(Guest guest) { em.persist(guest); } // Retrieves all the guests: public List ... - for storing a new  Guest entity object in the database. getAllGuests - for retrieving

); } // Retrieves all the guests: public List getAllGuests() { TypedQuery query = em.createQuery( "SELECT g FROM ... . getAllGuests - for retrieving all the existing Guest objects from the database. EJB classes

on every http request: The EntityManagerFactory is retrieved from the application scope attribute ... is constructed and stored in the database. All the Guest entity objects are retrieved from the database

that have already signed (which are retrieved from the request's guestDao attribute that is set by

 a Main class that stores and retrieves instances of the Point entity class.

. The next step is adding a Main class that stores and retrieves instances of the Point entity class.

( contextInitialized ). Retrieves the EntityManagerFactory from the application scope attribute and closes

This is the Eclipse version of the Quick Start with JPA tutorial. It demonstrates how to create and run a simple JPA application in Eclipse. The demonstrated application uses JPA to store and retrieve simple Point entity objects, where each Point has two persistent fields: x and y

that have already signed (which are retrieved from the request's "guests" attribute that is set by the servlet in

In this step we will add a main class to the project to store and retrieve Point objects from the database: Right click the tutorial package in the [Package Explorer] window and select New Class . The package name should be tutorial . Enter Main as the class name (case sensitive). Click Finish

In this step we will add code to the Main class (that was generated with the project) in order to store Point objects in the database and then retrieve them from the database. Use copy and paste to replace the content of the Main class with the following content: package tutorial; import javax

This tutorial demonstrates how to create and run a simple JPA application. The demonstrated application uses JPA to store and retrieve simple  Point entity objects, where each  Point has two persistent fields -  x and  y . If you already know JPA - the source code will be straightforward

that have already signed (which are retrieved from the request's "guests" attribute that is set by the servlet in

the guestbook, followed by a list of all the guests that have already signed (which are retrieved