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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


As explained in chapter 2, entity objects can be deleted from the database by: Retrieving ... an alternative way for deleting entity objects. Unlike SELECT queries, which are used to retrieve data from the database, DELETE queries do not retrieve data from the database, but when executed, delete specified

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

JPA Entity Fields

the database, but is still available after retrieval by a special automatic query. Note: Navigation ... . Instead, employees is automatically populated when a Department entity is retrieved from ... , the order of the retrieved owner entities can be set by the OrderBy annotation: @Entity public class

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

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

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

Step 3: Add a Main Class

to store Point objects in the database and then retrieve them from the database. Use copy and paste ... ()); // Retrieve all the Point objects from the database: TypedQuery<Point> query ... , and then run a few queries, including a query that retrieves all the 1000 Point objects from


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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