JPA mapping entities with hql column names

Question

I am trying to use a feature like RowMapper which provides me with ResultSet, so that I can set the attributes of my pojo by taking resultSet.getString("column_name") in JPA.

But JPA doesn't seems to provide such a feature.

StringBuffer rcmApprovalSqlString = new StringBuffer(QueryConstants.APPROVAL_DETAILS_SQL);
List<ApprovalDTO> finalApprovalList = null;

Query rcmApprovalTrailQuery = getEntityManager().createQuery(rcmApprovalSqlString.toString());
rcmApprovalTrailQuery.setParameter(1,formInstanceId);

List<?> approvalList = rcmApprovalTrailQuery.getResultList();
finalApprovalList = new ArrayList<ApprovalDTO>();
for(Object approvalObj : approvalList){
    Object[] obj = (Object[]) approvalObj;

    ApprovalDTO approvalDTO = new ApprovalDTO();
    approvalDTO.setDeptName(obj[0]!=null? obj[0].toString() : NAPSConstants.BLANK_STRING);
    approvalDTO.setUserId(obj[1]!=null? obj[1].toString()+" "+obj[2].toString() : NAPSConstants.BLANK_STRING);

    approvalDTO.setComment(obj[6]!=null? obj[6].toString() : NAPSConstants.BLANK_STRING);

    finalApprovalList.add(approvalDTO);
}

So instead of doing approvalDTO.setComment(obj[6]) which is the 6th element of array, can I do something like approvalDTO.setComment(rs.getString("comments")); ?

So if in future my column position change in the query, I will not have to change my DAO code to match the column number.

My hql query = select   ad.departmentid.departmentname, ad.userid.userfirstname, ad.userid.userlastname, ad.napsroleid.napsrolename, 
        ad.approvalstatus, ad.approvaltimestamp, ad.approvalcomments 
from    ApprovaldetailsTbl ad 
where   ad.forminstanceid.forminstanceid = ?1 
order by approvallevelid asc

Answer 1

With JPA 2.1 you have a great possibility to use SqlResultSetMapping . You can find out more for example here:

http://www.thoughts-on-java.org/2015/04/result-set-mapping-constructor.html

http://www.thoughts-on-java.org/2015/04/result-set-mapping-basics.html

http://www.thoughts-on-java.org/2015/04/result-set-mapping-complex.html

The idea is that instead of doing it as you used to do:

List<Object[]> results = this.em.createNativeQuery("SELECT a.id, a.firstName, a.lastName, a.version FROM Author a").getResultList();

    results.stream().forEach((record) -> {
            Long id = ((BigInteger) record[0]).longValue();
            String firstName = (String) record[1];
            String lastName = (String) record[2];
            Integer version = (Integer) record[3];
    });

you can introduce an annotation:

@SqlResultSetMapping(
        name = "AuthorMapping",
        entities = @EntityResult(
                entityClass = Author.class,
                fields = {
                    @FieldResult(name = "id", column = "authorId"),
                    @FieldResult(name = "firstName", column = "firstName"),
                    @FieldResult(name = "lastName", column = "lastName"),
                    @FieldResult(name = "version", column = "version")}))

and afterwards use the mapping (by specifying mapping name) in your query:

List<Author> results = this.em.createNativeQuery("SELECT a.id as authorId, a.firstName, a.lastName, a.version FROM Author a", "AuthorMapping").getResultList();

Answer 2

I am able to fetch the desired result only with Native query and not with NamedNativeQuery -

Query rcmApprovalTrailQuery = getEntityManager().createNativeQuery(rcmApprovalSqlString.toString(),"ApprovalMapping");
            rcmApprovalTrailQuery.setParameter(1,formInstanceId);

            List<ApprovaldetailsTbl> approvalList = rcmApprovalTrailQuery.getResultList();

My native query -

String RCM_APPROVAL_DETAILS_SQL = "select * "+
                " from  ApprovalDetails_TBL ad " +
                " where ad.ApprovalDetailsId = ? ";

SqlResultSetMapping -

@SqlResultSetMapping(name="ApprovalMapping",
        entities=@EntityResult(entityClass=ApprovaldetailsTbl.class
            ))

Note that you need to map all the column names to the entity field names if you are not using * in select query eg -

fields = {
                        @FieldResult(name = "col1", column = "alais1"),
                        @FieldResult(name = "col2", column = "alais2")})