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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The following annotations are used to define static named JPA queries: The JPA Named Queries section of the ObjectDB Manual explains and demonstrates how to use these annotations to define named JPQL queries.
The following interfaces are in use in representing general expressions in criteria queries: See the Query Expressions section for more details and examples.
The following JPA annotations are designated for SQL queries on relational databases: ObjectDB supports only the preferred JPA query language, JPQL, and silently ignores all the above annotations.
The FROM clause declares query identification variables that represent iteration over objects in the database. A query identification variable is similar to a variable of a Java enhanced for loop in a program, since both are used for iteration over objects. Range Variables Range variables are query
, the following query returns Country objects that become managed by the EntityManager em: TypedQuery<Country> query = em.createQuery("SELECT c FROM Country c", Country.class); List<Country> results = query.getResultList(); Because the results are managed entity objects they have all the support
javax.persistence Interface Query Subinterfaces: TypedQuery Interface used to control query execution. Since: JPA 1.0 See Also: TypedQuery Parameter Learn how to define and use JPA/JPQL queries in ... : IllegalStateException - if called for a Java Persistence query language SELECT statement or for a criteria
The GROUP BY clause enables grouping of query results. A JPQL query with a GROUP BY clause returns ... clause in the query execution order is after the FROM and WHERE clauses, but before the SELECT clause. When a GROUP BY clause exists in a JPQL query, database objects (or tuples of database objects
persisting objects in the database in more detail. JPA Queries with JPQL We can get the number of Point objects in the database by using a simple query: Query q1 = em.createQuery("SELECT COUNT(p) FROM Point p"); System.out.println("Total Points: " + q1.getSingleResult()); The query string ("SELECT
javax.jdo Interface Query Superinterfaces: Serializable The Query interface allows applications ... is the factory for Query instances. There may be many Query instances associated with a PersistenceManager. Multiple queries might be executed simultaneously by different threads
javax.jdo.annotations Annotation Query Target: Classes Annotation for a named query. Corresponds to the xml element "query". Since: JDO 2.1 Extension extensions Vendor extensions. Vendor extensions ... of the fetch plan used by this query The name of the fetch plan used by this query Returns: the fetch plan