Question

I have below SQL query:

SELECT * FROM (
  SELECT S.aCol, S.bCol, S.cCol, ROW_NUMBER() OVER (ORDER BY S.cCol ASC) AS R 
  FROM myTable S WHERE S.cCol LIKE 'abc%') AS TEMP 
WHERE R BETWEEN 0 AND 10 FOR FETCH ONLY

Basically this query serves pagination. The between clause will have different values for every fetch.

Now I want to implement the same query using JPA.

I found the below reference article from one SO question:

http://weblogs.java.net/blog/2007/05/31/pagination-data-sets-sample-application-using-jsf-catalog-facade-stateless-session-a

But in this article the resultant list is directly passed over to view. However, in my case I want to set the result columns in a transfer object (mySearchTO) as attributes.

Something like

mySearchTO.setBCol(resultSet.getString("B_COL"));
mySearchTO.setACol(resultSet.getString("A_COL")); 

in sql.

How to achieve this with JPA ?
Also, how can I write main query in JPA ?

I can not use Criteria Builder as I have to run my app on WSAD 6.1

The query which I am running is:

select s.aCol, s.bCol, s.cCol from MyEntity s  where s.cCol like 'abc' order by s.cCol asc

Above query is returning a List.

How to map it with my TO ?? I am trying

List<mySearchTO> myResult = new ArrayList<mySearchTO>();
myResult = myQuery.getResultList();

Where my TO class is a simple class with 3 properties (aCol, bCol and cCol) and getters and setters.

Error I am getting is

Exception thrown : java.lang.ClassCastException: [Ljava.lang.Object; incompatible with com.SummaryTO

But this is giving

Answer 1

JPA has pagination support with the Query.setFirstResult and Query.setMaxResults methods. I don’t know how it translates in SQL with DB2, though, but it’s done in database (using rownum with Oracle, limit with MySQL, etc.)

Just write your JPA query as you would do without pagination, and call these two methods, and Hibernate will generate the appropriate SQL query:

select s.aCol, s.bCol, s.cCol from MyEntity s 
where s.cCol like :pattern 
order by s.cCol asc