ObjectDB Database Search

The JPA Criteria API provides an alternative way for defining JPA queries , which is mainly useful for building dynamic queries whose exact structure is only known at runtime. JPA Criteria API vs JPQL JPQL queries are defined as strings, similarly to SQL. JPA criteria queries , on the other hand

The  Query and  TypedQuery interfaces define various setting and tuning methods that may affect query execution if invoked before a query is run using getResultList or getSingleResult ... defining a result window that exposes a portion of a large query result list (hiding

Query parameters enable the definition of reusable queries . Such queries can be executed with different parameter values to retrieve different results. Running the same query multiple times with different parameter values (arguments) is more efficient than using a new query string for every query

The Query interface defines two methods for running SELECT queries : Query .getSingleResult - for use when exactly one result object is expected. Query .getResultList - for general use in any ... - for general use in any other case. In addition, the Query interface defines a method for running

A named query is a statically defined query with a predefined unchangeable query string. Using named queries instead of dynamic queries may improve code organization by separating the JPQL query strings from the Java code. It also enforces the use of query   parameters

Queries are represented in JPA 2 by two interfaces - the old Query interface, which was the only interface available for representing queries in JPA 1, and the new TypedQuery interface that was introduced in JPA 2. The TypedQuery interface extends the Query interface. In JPA 2 the Query interface

Queries are represented in JPA by the Query and TypedQuery interfaces: The JPA Query API ... these interfaces to build and run JPQL queries . The TypedQuery interface (or alternatively the older Query interface) is the only neccessary interface for defining and running string based JPQL queries  

The syntax of the Java Persistence Query Language (JPQL) is very similar to the syntax of SQL. Having an SQL-like syntax in JPA queries is an important advantage because SQL is a very powerful query ... classes and objects. For example, a JPQL query can retrieve and return entity objects

DELETE queries provide 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 ... from the database using a DELETE query may be slightly more efficient than retrieving entity objects

;within an active transaction. Applying changes to the database by calling the commit method. JPQL UPDATE queries provide 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

Query expressions are the foundations on which JPQL and criteria queries are built. Every query ... of JPQL / Criteria query expressions. Atomic Expressions The atomic query expressions are: JPQL / Criteria Variables JPQL / Criteria Parameters JPQL / Criteria Literals Every query expression consists

The JPA Query Language (JPQL) can be considered as an object oriented version of SQL. Users ... well as how to use the JPA Criteria API, which provides an alternative way for building queries in JPA ... (named) queries . It explains how to use the relevant interfaces, annotations, enums and methods

and for representing query results as tuples. SELECT Clause Elements The content of the SELECT clause in a criteria query is represented by Selection : Because Selection  is a super interface ... of Selection : See the SELECT in Criteria Queries section for more details and examples. ORDER BY

The interfaces in this group are in use for setting a criteria query FROM clause. Criteria Query Variables The FROM clause  in JPA queries (as in SQL) defines the query variables. Query variables are represented in criteria queries by descendant interfaces of the From interface: Range

Date and time expressions may appear in JPQL queries : as date and time literals - e.g. {d '2011-12 ... that are evaluated to the date and time on the database server when the query is executed: CURRENT_DATE ... to 0 . Date and Time in Criteria Queries The CriteriaBuilder interface provides three factory methods

Collections may appear in JPQL queries : as parameters - when collections are assigned as arguments ... that is passed to the query as a parameter. For example: 'English' IN :languages is TRUE if the argument ... are treated as synonyms. Criteria Query Collection Expressions JPQL collection operators and functions

). JPQL literals should be used sparingly as queries that use parameters instead of literals ... parameter values. Literals should only be embedded in JPQL queries when a single constant value ... '} Enum Literals JPA 2 adds support for enum literals. Enum literals in JPQL queries use

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 .

String values may appear in JPQL queries in various forms: as  string literals - e.g. 'abc ... expressions (which are more powerful than the LIKE operator). Criteria Query String Expressions JPQL string operators and functions (which are described above) are available also as JPA criteria query

Numeric values may appear in JPQL queries in many forms: as  numeric literals - e.g. 123 ... . Criteria Query Arithmetic Expressions JPQL arithmetic operators and functions (which are described above) are available also as JPA criteria query expressions. The CriteriaBuilder interface provides

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 following query returns Country objects that become managed by the EntityManager em : TypedQuery query = em. createQuery ("SELECT c FROM Country c", Country.class); List results = query . getResultList ... detection , support for delete , etc. Query results are not limited to entity objects. JPA 2 adds

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 ... are query identification variables that iterate over all the database objects of a specific entity

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

, derived attributes, grouping queries and aggregate queries ) which are usually missing from Object Oriented ... . Query program cache (for repeating queries with different arguments). Query result cache (for repeating queries with the same arguments). Many other internal caches. Indexing Single field and multi field

to view data in ObjectDB databases, execute JPQL and JDOQL queries and edit the content of databases ... and embeddable classes) in the database and their persistent fields and indexes. The [ Query ] window enables running JPQL and JDOQL queries , as discussed below. Closing a Database Connection Use the File Close

JPQL query that retrieves selective objects from the database. Out of the four optional clauses of JPQL queries , the WHERE clause is definitely the most frequently used. How a WHERE Clause Works The following query retrieves only countries with a population size above a population size p

The ORDER BY clause specifies a required order for the query results. Any JPQL query that does not ... Expressions The following query returns names of countries whose population size ... expressions in the SELECT clause are allowed in the ORDER BY clause. The following query , for example

(which modify the database) have to be recorded. For debugging of query failure ... to accelerate the execution of relevant queries . The element The element specifies settings of the two cache mechanisms that ObjectDB manages for queries : The results attribute specifies the size

, string, date). Simple type values are more useful in queries . They have special operators ... ). Navigation through a NULL value The following query retrieves country names with their capital city names ... the equivalent JOIN query . Entity Type Expressions The TYPE operator (which is new in JPA 2) returns the type

JPA Interface Query Interface used to control query execution. See Also: TypedQuery StoredProcedureQuery Parameter Since: JPA 1.0 Chapter 4 - JPA Queries (JPQL / Criteria) explains how to use Query ... of entities updated or deleted Throws: IllegalStateException - if called for a Java Persistence query

. When a more selective retrieval is needed, JDOQL (JDO Query Language) is used. JDOQL for JDO is like ... a specified order. 7.1  Introduction to JDOQL A basic JDOQL query has the following ... (usually a persistent class) A filter, which is a boolean expression in a Java like syntax The query

after retrieval by a special automatic query . Note : Navigation through inverse fields is much less efficient than navigation through ordinary persistent fields, since it requires running queries . Inverse ... the following query (where :d represents the Department entity): SELECT e FROM Employee e WHERE e

Querying without indexes requires iteration over entity objects in the database one by ... indexes the iteration can be avoided and complex queries over millions of objects can be executed quickly ... firstName; String lastName; Address address; : } Indexes in Queries ObjectDB manages a BTree

. Starting Online Backup The online backup can be started by executing a special query on an EntityManager ... ; em.createQuery("objectdb backup").getSingleResult(); The backup query string is always exactly ... directory can be specified by setting the target parameter before executing the backup query :  

Logical operators in JPQL and in JPA criteria queries enable composition of complex JPQL boolean ... , the JDO Query Language). ObjectDB supports both forms. Binary AND (&&) Operator The following query retrieves countries whose population and area (both) exceed specified limits: SELECT c FROM

;name,     Query   query ) Define the query , typed query , or stored procedure query as a named query such that future query objects can be created from it using the createNamedQuery or createNamedStoredProcedureQuery method. Any configuration of the query object (except for actual

JPA Method in javax.persistence. Query Query setLockMode (    LockModeType  lockMode ) Set the lock mode type to be used for the query execution. Parameters: lockMode - lock mode Return: the same query instance Throws: IllegalStateException - if the query is found not to be a Java

JPA Method in javax.persistence. Query Stream getResultStream () Execute a SELECT query and return the query results as an untyped java.util.stream.Stream . By default this method delegates ... for a Java Persistence query language UPDATE or DELETE statement QueryTimeoutException - if the query

JPA Method in javax.persistence. Query List getResultList () Execute a SELECT query and return the query results as an untyped List. Return: a list of the results Throws: IllegalStateException - if called for a Java Persistence query language UPDATE or DELETE statement QueryTimeoutException

and the other for checking a persistent field of an entity object. Retrieval by Query The most flexible method for retrieving objects from the database is to use queries . The official query language of JPA is JPQL (Java Persistence Query Language). It enables retrieval of objects from the database by

of NoSQL technology, which are weak query capabilities and lack of ACID (atomicity, consistency, isolation, durability). Unlike other NoSQL solutions, ObjectDB provides full support of rich complex queries , using two standard Java query languages: JPQL (Java Persistence Query Language) and JDOQL (JDO

to browse databases, execute JDOQL queries , create new databases and edit the content of existing ... to explore database objects visually, navigate among them and execute queries is very valuable ... that the database contains (root objects are discussed in chapter 6 ). The " Query " window enables a user

JDO Interface Query Super Interfaces: 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, but the implementation

classes are not included in the extents of their classes, so they cannot be iterated or queried directly ... one. If more selective retrieval is needed, a Query can be used to retrieve only objects that satisfy some ... (the commented line in the code above). Retrieval by Query The most advanced method for retrieving objects from

of queries against the class instances. However, maintaining an extent for a class has some overhead ... are not included in the extents of their classes, so they cannot be queried directly. When the embedded ... ;Index Definition Querying a large extent without indexes may take a significant amount of time

JDO Method in javax.jdo. Query void addSubquery (    Query  sub,     ... ;   String... parameters ) Add a subquery to this query . A subquery is composed as a Query and subsequently attached to a different query (the outer query ) by calling this method. The query

JDO Annotation Query Target: ElementType.TYPE Implemented Interfaces: Annotation Annotation for a named query . Corresponds to the xml element " query ". Since: JDO 2.1 Public Annotation Attributes ... "" The name of the fetch plan used by this query Since: JDO 2.1 String language default "JDOQL" The query

JDO Method in javax.jdo. Query void addSubquery (    Query  sub,     ... ;   Map parameters ) Add a subquery to this query . The Map version of the method treats ... ":", and the value as the name of the expression in the outer query . If the trimmed expression