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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

Entity objects are in-memory instances of entity classes (persistable user defined classes), which can represent physical objects in the database. Managing an ObjectDB Object Database using JPA requires using entity objects for many operations, including storing, retrieving, updating and deleting

Detached entity objects are objects in a special state in which they are not managed by any EntityManager but still represent objects in the database. Compared to managed entity objects , detached objects are limited in functionality: Many JPA methods do not accept detached objects (e.g. lock

New entity objects can be stored in the database either explicitly by invoking the persist method ... (). commit (); The Employee instance is constructed as an ordinary Java object and its initial state is New. An explicit call to persist associates the object with an owner EntityManager em and changes

Existing entity objects can be deleted from the database either explicitly by invoking the remove ... an object from the database it has to first be retrieved (no matter which way) and then in an active ... object is physically deleted from the database when the transaction is committed. Embedded objects

, derived attributes, grouping queries and aggregate queries) which are usually missing from Object Oriented Databases are also supported by ObjectDB. The combination of Object Database features ... . Up to 9,223,372,036,854,775,808 entity objects per database file. Unlimited database connections

Modifying 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

solution. Using a relational database management system (RDBMS) to store and retrieve Java objects requires slow conversions between graphs of Java objects and flat database table rows. Object Relational ... , and even add their own overhead. ObjectDB supports direct storage of graphs of objects

. However, you should consider the following points when doing your own objective comparison of object databases: ObjectDB is unique in supporting the standard APIs. It is the only object database with built in ... of the Java Data Objects (JDO) API than competing object databases. By using a standard API such as JPA

All about Is ObjectDB better than Object Relational Mapping (ORM)? in Java/JPA database - explanations, examples, references, links and related information.

of bookmarked entity objects . The [Schema] window shows the user defined persistable types (entity ... a single object , every column represents a persistent field, and the content of a cell is the value of a single field in a single database object . This type of viewer is useful for viewing data of a simple

The ability to retrieve managed entity objects is a major advantage of JPQL. For example, the following query returns Country objects that become managed by the EntityManager em : TypedQuery query ... (); Because the results are managed entity objects they have all the support that JPA provides

This chapter describes how to use ObjectDB to manage database objects . 6.1  Making Objects Persistent In JDO applications, every object in memory is either a persistent object , i.e. represents some database content, or a transient object , i.e. not related to any database. Storing Objects

Every entity object that is stored in the database has a primary key. Once assigned, the primary key cannot be modified. It represents the entity object as long as it exists in the database. As an object database, ObjectDB supports implicit object IDs, so an explicitly defined primary key is not

in ObjectDB (and in JPA) is always at the database object level, i.e. each database object is locked separately. Optimistic locking is applied on transaction commit. Any database object ... is being performed on an old version of a database object , for which another update has already been committed

The FROM clause declares query identification variables that represent iteration over objects in ... a program, since both are used for iteration over objects . Range Variables Range variables are query identification variables that iterate over all the database objects of a specific entity

The Java Data Objects (JDO) is another standard for accessing persistent data in databases, using plain old Java objects (POJO) to represent the object model. Unlike Java Persistence API (JPA ... with both relational and object databases. JDO is supported by many object databases, including ObjectDB

properties of generated groups instead of individual objects and fields. The position of a GROUP BY ... clause. When a GROUP BY clause exists in a JPQL query, database objects (or tuples of database objects ... over all the Country objects in the database. The GROUP BY clause groups these Country objects by

- for use when exactly one result object is expected. Query.getResultList - for general use in any ... - for use when exactly one result object is expected. TypedQuery.getResultList - for general use in any ... (with getResultList) The following query retrieves all the Country objects in the database. The query

Every EntityManager owns a persistence context , which is a collection of all the entity objects ... an entity object that is already managed by the  EntityManager returns the existing instance from the persistence context, rather than a newly instantiated entity object . The scope of the persistence

are assigned as arguments. Path expressions that navigate from one object to another. Instances of user ... expression) and uses the dot ( . ) operator to navigate through persistent fields to other objects and values. For example - c.capital , where c represents a Country entity object uses the capital

the @Transient annotation). Storing an entity object in the database does not store methods or code. Only the persistent state of the entity object , as reflected by its persistent fields (including persistent fields that are inherited from ancestor classes), is stored. When an entity object is stored in

As explained in chapter 2 , entity objects can be deleted from the database by: Retrieving the entity objects into an EntityManager . Removing these objects from the EntityManager   ... DELETE queries provide an alternative way for deleting entity objects . Unlike SELECT queries

To be able to store Point objects in the database using JPA we need to define an entity class . A JPA entity class is a POJO (Plain Old Java Object ) class, i.e. an ordinary Java class that is marked (annotated) as having the ability to represent objects in the database. Conceptually

of an entity class are detected by ObjectDB. New entity objects have to be stored in the new class schema, and old entity objects , which were stored previously in the old class schema ... that enables transparent use of old entity objects after schema change. When an entity object

objects of the subclasses unless that callback method is overridden by the subclass. Implementation ... methods and should not access any other entity objects . If a callback method throws an exception ... onPrePersist( Object o) {} @PostPersist void onPostPersist( Object o) {} @PostLoad void onPostLoad( Object o

Existing entity objects can be updated, as explained in chapter 2 , by: Retrieving the entity objects into an EntityManager . Updating the relevant entity object fields  ... provide an alternative way of updating entity objects . Unlike SELECT queries, which are used

classes and objects . For example, a JPQL query can retrieve and return entity objects rather than just field values from database tables, as with SQL. That makes JPQL more object oriented friendly ... 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 ... over all the Country objects in the database using the c range variable. Before passing these Country objects to the SELECT clause for collecting as query results, the WHERE clause gets an opportunity

to software source code, documentation source, and configuration files. " Object " form shall mean any form ... to compiled object code, generated documentation, and conversions to other media types. "Work" shall mean the work of authorship, whether in Source or Object form, made available under the License, as

in Query and TypedQuery support method chaining (by returning the query object ... automatic optimistic locking to prevent concurrent changes to entity objects by multiple users. JPA 2 ... on all the result objects that the query retrieves. For example, the following query execution sets

Querying without indexes requires iteration over entity objects in the database one by one. This may take a significant amount of time if many entity objects have to be examined. Using proper indexes the iteration can be avoided and complex queries over millions of objects can be executed quickly

ObjectDB is an Object Oriented Database Management System (ODBMS). It provides all the standard ... , etc.), but it uses an object oriented model to store and manage data. You can easily store ordinary objects (and graphs of objects ) in an ObjectDB database directly. There's no need to define tables

) The following method retrieves a Country object from the database by its name: public Country ... ). getSingleResult (); } The WHERE clause reduces the query results to Country objects whose name field value ... that is built by using the JPA Criteria API - parameters (as other query elements) are represented by objects

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

JPA exceptions are represented by a hierarchy of unchecked exceptions: java.lang. Object java.lang ... because of an attempt to store a new entity object with a primary key that is already in use by another existing entity object , the nested exception is: Other common causes for RollbackException are lock failures

class can only be stored in the database as embedded objects , i.e. as part of a containing entity object . A class is declared as embeddable by marking it with the Embeddable annotation: @Embeddable ... of embeddable classes are always embedded in other entity objects and do not require separate space

number generator for every database. This number generator is used to generate automatic object IDs for entity objects with no primary key fields defined (as explained in the previous section ). The same ... for every new entity object . These generated values are unique at the database level and are never recycled

results and the lowest known common denominator of all the result objects is Object ... which retrieves all the Country objects in the database is represented by both q1 and q2 . When building ... objects ), a TypedQuery is preferred. There is another advantage of using  TypedQuery  in

) is that in JPA data is represented by classes and objects rather than by tables and records as in JDBC. Using plain old Java objects (POJO) to represent persistent data can significantly simplify ... . These implementations are Object Relational Mapping (ORM) tools. The mapping bridges between the data

. The ability to store ordinary objects in the database directly can simplify the code significantly ... ObjectDB is especially designed to store and manage graphs of objects efficiently. That can accelerate the execution time of object oriented applications significantly. For instance, collection and map

objects visually, navigate among them and execute queries is very valuable during development ... information about the database and the bottom sub window displays a list of root objects that the database contains (root objects are discussed in chapter 6 ). The "Query" window enables a user to execute

, which are defined in the JDO specification, are ignored by ObjectDB if specified (as a pure object database, ObjectDB always uses datastore identity with its own object -id class). 4.3   ... and persistent in JDO), or a field whose declared type is java.lang. Object or some interface, but holds

There are various ways to retrieve objects from an ObjectDB database, as shown in section 6.3 ... SQL for RDBMS. It provides object retrieval from the database according to a specified selectioPlan ... three components: A candidate collection containing persistent objects (usually an Extent ) A candidate class

. Instances of these classes that represent objects in the database are called persistent objects or persistent instances . Objects that do not represent anything in the database (including instances of persistent classes that live only in memory) are called transient objects or transient instances

storing, retrieving, updating and deleting database objects , are provided in the next chapter ... , but to make your application JDO portable these objects are accessed through the standard JDO interfaces ... on any PersistenceManager instance, in any context, to return its associate Transaction object

object database, can simply store a memory data structure in the database as is. If the database is not ... ). An object bound to the database during an active transaction, is expected to be stored physically in the database when the transaction is committed (line 37). Note: Memory objects that represent database

ObjectDB for Java/JDO is a powerful Object Database Management System (ODBMS) written entirely in ... of them. ObjectDB is an Object Database Developing object oriented applications with ObjectDB is easier and much more effective because the content of the database is application objects

You can use ObjectDB with either the Java Persistence API (JPA) or the Java Data Objects (JDO) API ... , tutorials and sample 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

An object ID is a combination of a persistence capable class and a primary key. It provides a unique representation of a persistent object . The following classes serve as predefined ID classes for persistence capable classes with a simple single field primary key: Object IDs are used in many