Difference between revisions of "EclipseLink/Examples/JPA/Pagination"

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There are a variety of solution options for paging results in an EclipseLink JPA application. This how-to highlights various approaches with code samples of how they can be used.  
 
There are a variety of solution options for paging results in an EclipseLink JPA application. This how-to highlights various approaches with code samples of how they can be used.  
  
 
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== FirstResult/MaxRows ==
 
== FirstResult/MaxRows ==

Revision as of 12:16, 29 March 2008

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How to use EclipseLink Pagination

There are a variety of solution options for paging results in an EclipseLink JPA application. This how-to highlights various approaches with code samples of how they can be used.

Contents


FirstResult/MaxRows

Database Specific SQL

EclipseLink's target database platform enables the generation of native SQL that can more optimally retrieve a set of rows.

Oracle ROWNUM

When the target platform is Oracle then ROWNUM is used in the generated SQL in addition to a hint to retrieve a page of results.

		Query query = em
				.createQuery("SELECT e FROM Employee e ORDER BY e.lastName ASC, e.firstName ASC");
		query.setFirstResult(5);
		query.setMaxResults(5);
		List<Employee> emps = query.getResultList();

Generates the SQL like:

SELECT * FROM (SELECT /*+ FIRST_ROWS */ a.*, ROWNUM rnum  FROM (
	SELECT  t0.EMP_ID AS EMP_ID1, t1.EMP_ID AS EMP_ID2, t0.F_NAME AS F_NAME3, t0.L_NAME AS L_NAME4, t0.START_TIME AS START_TIME5, 
		t0.END_TIME AS END_TIME6, t0.GENDER AS GENDER7, t1.SALARY AS SALARY8, t0.VERSION AS VERSION9, t0.START_DATE AS START_DATE10, 
		t0.END_DATE AS END_DATE11, t0.MANAGER_ID AS MANAGER_ID12, t0.ADDR_ID AS ADDR_ID13 
	   FROM EMPLOYEE t0, SALARY t1 
	   WHERE (t1.EMP_ID = t0.EMP_ID) ORDER BY t0.L_NAME ASC, t0.F_NAME ASC) a WHERE ROWNUM <= ?) WHERE rnum > ?

	bind => [10, 5]

Chunking using PKs with IN

This involve performing a query on the database for all of the primary key values that match the criteria and then using these values to retieve specific sets.

		Query query = em
				.createQuery("SELECT e.id FROM Employee e ORDER BY e.lastName ASC, e.firstName ASC");
		List<Integer> empIds = query.getResultList();
		
		ReadAllQuery raq =  new ReadAllQuery(Employee.class);
		ExpressionBuilder eb = raq.getExpressionBuilder();
		raq.setSelectionCriteria(eb.get("id").in(empIds.subList(5, 10)));
		List<Employee> emps = JpaHelper.createQuery(raq, em).getResultList();

The SQL generated for this query looks like:

SELECT t0.EMP_ID FROM EMPLOYEE t0, SALARY t1 WHERE (t1.EMP_ID = t0.EMP_ID) ORDER BY t0.L_NAME ASC, t0.F_NAME ASC


SELECT t0.EMP_ID, t1.EMP_ID, t0.F_NAME, t0.L_NAME, t0.START_TIME, t0.END_TIME, t0.GENDER, t1.SALARY, t0.VERSION, 
       t0.START_DATE, t0.END_DATE, t0.MANAGER_ID, t0.ADDR_ID FROM EMPLOYEE t0, SALARY t1 
    WHERE ((t0.EMP_ID IN (?, ?, ?, ?, ?)) AND (t1.EMP_ID = t0.EMP_ID))
	
    bind => [8, 1, 12, 3, 10]