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Existing entity objects can be updated, as explained in chapter 2, by: Retrieving the entity ... an alternative way of updating entity objects. Unlike SELECT queries, which are used to retrieve data from the database, UPDATE queries do not retrieve data from the database, but when executed, update

JPA Primary Key

the database is uniquely identified (and can be retrieved from the database) by the combination of its type ... is required if entity objects have to be retrieved by their primary key as shown in the Retrieving ... that queries that retrieve all the events of a specified sensor in a specified period are common

SELECT clause (JPQL / Criteria API)

The ability to retrieve managed entity objects is a major advantage of JPQL. For example ... are also supported. For example, the following query retrieves the name of the capital city ... with the containing entities. Therefore, embedded objects that are retrieved directly by a result path expression

FROM clause (JPQL / Criteria API)

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

Logical Operators in JPQL and Criteria API

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 FROM ... retrieves all the countries whose population does not exceed a specified limit: SELECT c FROM

JPA Query Structure (JPQL / Criteria)

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 ... JPQL Query The following query retrieves all the Country objects in the database: SELECT c FROM

WHERE clause (JPQL / Criteria API)

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: SELECT c ... them to the SELECT clause. For example, the following query retrieves all the countries with population size

Step 3: Add a Main Class

In this step we will add a main class to the project to store and retrieve Point objects from ... "); System.out.println("Average X: " + q2.getSingleResult()); // Retrieve all the Point objects from ... 1000 Point objects in the database, and then runs a few queries, including a query that retrieves


JDO JavaDoc Reference Documentation -


retrieve(Object pc) Retrieve field values of an instance from the store. Retrieve field values ... 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 void

Getting Started

ObjectDB is very easy to use. Follow the Getting Started Tutorial and the Quick Tour manual chapter and in minutes you may be able to write and run first Java programs against ObjectDB.

Prior knowledge or experience in database programming (SQL, JDBC, ORM, JPA, etc.) is not required, but some background in using the Java language is essential.

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