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Manual
19

Retrieving JPA Entity Objects

The Java Persistence API (JPA) provides various ways to retrieve objects from the database ... with data that is retrieved from the database (or from the L2 cache - if enabled). The new entity object ... as is. Otherwise, the object data is retrieved from the database and a new managed entity object
Manual
18

SELECT clause (JPQL / Criteria API)

query = em.createQuery("SELECT c FROM Country c", Country.class); ListFROM Country AS c Using path expressions, such as c.name, in query results is referred to as projection. The field values are extracted from (or projected out of) entity objects to form the query
Manual
18

Paths and Types in JPQL and Criteria API

classes) are represented in JPQL by the following types of expressions: Variables - FROM ... as arguments. Path expressions that navigate from one object to another. Instances of user defined ... .capital.name is a nested path expression that continues from the Capital entity object to its name
Manual
16

ORDER BY clause (JPQL / Criteria API)

is at least one million people, ordered by the country name: SELECT c.name FROM Country c WHERE c.population > 1000000 ORDER BY c.name When an ORDER BY clause exists it is the last to be executed. First the FROM ... directly from expressions in the SELECT clause are allowed in the ORDER BY clause. The following query
Forum
16

Delete object from collection versus delete from JPQL

Delete object from collection versus delete from JPQL
Manual
16

DELETE Queries in JPA/JPQL

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 within an active ... an alternative way for deleting entity objects. Unlike SELECT queries, which are used to retrieve data from
Manual
16

WHERE clause (JPQL / Criteria API)

The WHERE clause adds filtering capabilities to the FROM-SELECT structure. It is essential in any JPQL query that retrieves selective objects from the database. Out of the four optional clauses ... , which is represented by the parameter p: SELECT c FROM Country c WHERE c.population > :p The FROM clause
Manual
15

GROUP BY and HAVING clauses

clause in the query execution order is after the FROM and WHERE clauses, but before the SELECT ... ) that are generated by the FROM clause iteration and pass the WHERE clause filtering (if any) are sent ... .name, 1, 1) FROM Country c GROUP BY SUBSTRING(c.name, 1, 1); The FROM clause defines iteration
Manual
13

Database Schema Evolution

), a conversion is required. If the old type is inconvertible to the new type (for instance a change from ... with a default value (0, false or null). The following type conversions are supported: From any numeric type ... that are stored as numeric ordinal values (the default). From any type to Boolean or boolean (0, null
Manual
13

CRUD Database Operations with JPA

objects in the database by using a simple query: Query q1 = em.createQuery("SELECT COUNT(p) FROM Point ... COUNT(p) FROM Point p") instructs JPA to count all the Point objects in the database. If you have used ... of a query that returns a single result: Query q2 = em.createQuery("SELECT AVG(p.x) FROM Point p