1. Enterprise Java v041102EJB QL1 EJB Query Language Source: “Enterprise JavaBeans, 3rd Edition”, Richard Monson-Haefel

2. Enterprise Java v041102EJB QL2 Finder Methods Container can implement findByPrimaryKey public interface PersonLocalHome extends EJBLocalHome { PersonLocal create(String id) throws CreateException; PersonLocal create(String id, String firstName, String lastName, String address, String phoneNumber) throws CreateException; PersonLocal findByPrimaryKey(PersonPK pkey) throws FinderException; } public interface PersonRemoteHome extends EJBHome { PersonRemote create(String id) throws CreateException, RemoteException; PersonRemote create(Person values) throws CreateException, RemoteException; PersonRemote findByPrimaryKey(PersonPK pkey) throws FinderException, RemoteException; }

3. Enterprise Java v041102EJB QL3 Finder Methods Container cannot implement custom finders public interface PersonLocalHome extends EJBLocalHome {... PersonLocal findByName(String firstName, String lastName) throws FinderException; Collection findAll() throws FinderException; Collection findByAddress(String address) throws FinderException; } public interface PersonRemoteHome extends EJBHome {... PersonRemote findByName(String firstName, String lastName) throws FinderException, RemoteException; Collection findAll() throws FinderException, RemoteException; Collection findByAddress(String address) throws FinderException, RemoteException; }

4. Enterprise Java v041102EJB QL4 EJB Query Language There was no portable way to express query methods prior to EJB2.0 Used to express the behavior of query methods –custom finders declared in EJBHome/EJBLocalHome –Select methods (added in EJB2.0) as functional as custom finders, but adds more power –can return objects, object attributes, and objects not of the scoping class –usable only by the EJB class declared in EJB class as an abstract method

5. Enterprise Java v041102EJB QL5 EJB Query Language (cont.) Expressed in terms of the Java Abstract Schema and not the database schema Robust, while remaining portable across databases of different technologies –However, not without limitations Ordering (Addressed in EJB 2.1) Date compares Dynamic String likes (LIKE operation can not be used with input parameters) Queries are statically compiled. However, most vendors allow EJB-QL statements to be created dynamically.

6. Enterprise Java v041102EJB QL6 Defined in ejb-jar.xml Person … Person firstName lastName......

7. Enterprise Java v041102EJB QL7 Defined in ejb-jar.xml findByName java.lang.String SELECT OBJECT(p) FROM Person p WHERE p.firstName = ?1 AND p.lastName = ?2

8. Enterprise Java v041102EJB QL8 Find Methods Invoked by EJB Clients to obtain local or remote object references to specific objects Return object reference for single object finds public interface PersonLocalHome extends EJBLocalHome { PersonLocal findByName(String firstName, String lastName) throws FinderException; public interface PersonRemoteHome extends EJBHome { PersonRemote findByName(String firstName, String lastName) throws FinderException, RemoteException; –Throws FinderException on application error –Throws ObjectNotFoundException when object not found

9. Enterprise Java v041102EJB QL9 Find Methods (cont.) Return Collection type for multi-object finds public interface PersonLocalHome extends EJBLocalHome { Collection findByAddress(String address) throws FinderException; public interface PersonRemoteHome extends EJBHome { Collection findByAddress(String address) throws FinderException, RemoteException; –Collections may return duplicates (use DISTINCT in query expression to eliminate) Throws FinderException on application error Returns empty Collection when no objects found

10. Enterprise Java v041102EJB QL10 Select Methods Private query methods of the EJB class –not directly exposed in any of the bean’s interfaces Operate within the transaction that calls it –Finder methods execute within the transaction context individually defined for them Can return CMP fields as well as CMR objects – for single-object selects –java.util.Collection for multi-object selects –java.util.Set for distinct multi-object selects List and Map are being considered for future releases

11. Enterprise Java v041102EJB QL11 Select Methods (cont.) Returns either remote or local object –local by default –remote if is selected

12. Enterprise Java v041102EJB QL12 Select Method Example Declare abstract Select method in the EJB Class public abstract class PersonEJB implements PersonLBI, PersonBI, EntityBean { public abstract Set ejbSelectPhoneNumbers() throws FinderException; Define the Select Method in ejb-jar.xml ejbSelectPhoneNumbers SELECT DISTINCT p.phoneNumber FROM Person p

13. Enterprise Java v041102EJB QL13 Select Method Example Declare a home method that accesses the Select method public interface PersonRemoteHome extends EJBHome { Set getPhoneNumbers() throws FinderException, RemoteException; public interface PersonLocalHome extends EJBLocalHome { Set getPhoneNumbers() throws FinderException; Define the method in the EJB Class public Set ejbHomeGetPhoneNumbers() throws FinderException { return ejbSelectPhoneNumbers(); }

14. Enterprise Java v041102EJB QL14 EJB QL Basics SELECT OBJECT(p) from Person AS p –selects all person objects from the database –returns collection of either local/remote object references –OBJECT() required for non-Path expressions –Person comes from abstract-schema-name –AS is optional –p must not appear in abstract schema of class –p is not case-sensitive SELECT OBJECT(person) from Person person //illegal

15. Enterprise Java v041102EJB QL15 EJB QL with Paths SELECT p.phoneNumber FROM Person p –selects phone number attributes for all persons in the database –returns a collection of java.lang.Strings (based on abstract schema mapping for phoneNumber) SELECT b.identity FROM Borrower b –selects person objects for all borrowers in the database –returns a collection of PersonLocal (or PersonRemote) (based on context of call or return-type-mapping attribute) –OBJECT() not used here

16. Enterprise Java v041102EJB QL16 FROM IN Operator Illegal to navigate relationship from SELECT clause –SELECT b.checkouts FROM Borrower b //illegal –SELECT b.checkouts.outSQLDate FROM Borrower b //illegal and doesn’t make sense

17. Enterprise Java v041102EJB QL17 FROM IN Operator FROM IN(…) AS –SELECT OBJECT(co) FROM Borrower b, IN (b.checkouts) AS co –SELECT co.outSQLDate FROM Borrower b, IN(b.checkouts) AS co Assigns CMR fields to identifier

18. Enterprise Java v041102EJB QL18 DISTINCT SELECT DISTINCT p.phoneNumber FROM Person p –DISTICT keyword prevents the query from returning duplicate elements –redundant for Set return types

19. Enterprise Java v041102EJB QL19 Literal WHERE Clauses SELECT OBJECT(p) FROM Person p WHERE p.firstName = ‘cat’ –escape ‘ with `` to implement searching for O’cat WHERE p.firstName = ‘O’’cat’

20. Enterprise Java v041102EJB QL20 Parameterized Where Clauses findByName java.lang.String SELECT OBJECT(p) FROM Person p WHERE p.firstName = ?1 AND p.lastName = ?2

21. Enterprise Java v041102EJB QL21 CDATA Sections <![CDATA[ SELECT OBJECT(c) FROM Checkout c WHERE c.outSQLDate < ?1 ]]>

22. Enterprise Java v041102EJB QL22 WHERE Clauses Arithmetic Operators –SELECT OBJECT(s) FROM Seat s WHERE (s.price *.04) > 1.00 Logical Operators –SELECT OBJECT(p) FROM Person p WHERE p.firstName = ?1 AND p.lastName = ?2 Comparisons (must be of same type) –boolean and String: =, <>, NO relative comparisons –numeric: =, >, >=,

23. Enterprise Java v041102EJB QL23 WHERE Clauses (cont.) BETWEEN –SELECT OBJECT(s) FROM Seat s WHERE s.price BETWEEN 1.00 AND 10.00 IN –SELECT OBJECT(p) FROM Person p WHERE p.firstName IN (‘cat’, ‘thing’) –SELECT OBJECT(p) FROM Person p WHERE p.firstName NOT IN (‘cat’, ‘thing’) IS NULL –SELECT OBJECT(b) FROM Borrower b WHERE b.identity IS NULL

24. Enterprise Java v041102EJB QL24 WHERE Clauses (cont.) IS EMPTY –SELECT OBJECT(b) FROM Borrower b WHERE b.checkouts IS EMPTY MEMBER OF (p. 248 Monson-Haefel) SELECT OBJECT(crs) FROM Cruise crs, IN(crs.reservations) res, Customer cust WHERE cust=?1 AND cust MEMBER OF res.customers Finds whether a Customer (input parameter to finder) is a member of any reservation-customer relationships LIKE –SELECT Object(p) FROM Person p WHERE p.firstName like ‘c%’ //finds cat WHERE p.firstName like ‘c_t’ //finds cat WHERE p.firstName like ‘\%c%` //finds %c...

25. Enterprise Java v041102EJB QL25 EJB QL Shortfalls No Date compare –must implement as a long compare storing Date.getTime() No dynamic LIKE –identified solution LIKE (CONCAT('%foo', ?1)) Limited Functions –EJB 2.1 added aggregate functions like COUNT, MAX, AVG and SUM. Still missing functions like UPPER and LOWER are still not supported