Pagination not working for a Lazy Loaded Data Table on First Loading - jpa

Question

I am using JPA named queries for Loading a Lazy Loaded DataTable. and setting first and Max results as shown below.
Query query = entityManager.createNamedQuery("StudyplanCategory.findByStatusAndLimit");
int end=(start*pageNumber);
query.setParameter("status", status);
query.setParameter("start", start);
query.setParameter("end", end);
query.setMaxResults(end - start);
The load method is given below:
public List<StudyplanCategory> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String,String> filters) {
List<StudyplanCategory> data = new ArrayList<StudyplanCategory>();
//System.out.println("Page First Value:"+first+"PageSize Value:"+pageSize);
datasource=categoryService.findDynaEditStudyPlan("NOT_USER_SPECIFIC",first,pageSize);
//filter
for(StudyplanCategory studyplanCategory : datasource) {
boolean match = true;
for(Iterator<String> it = filters.keySet().iterator(); it.hasNext();) {
try {
String filterProperty = it.next();
String filterValue = filters.get(filterProperty).toLowerCase();
String fieldValue = String.valueOf(studyplanCategory.getClass().getDeclaredField(filterProperty).get(studyplanCategory)).toLowerCase();
//System.out.println("fieldValue............."+fieldValue);
if(filterValue == null || fieldValue.startsWith(filterValue)) {
match = true;
}
else {
match = false;
break;
}
} catch(Exception e) {
match = false;
System.out.println("The Exception occured at"+e);
}
}
if(match) {
data.add(studyplanCategory);
}
}
//sort
if(sortField != null) {
Collections.sort(data, new LazySorter(sortField, sortOrder));
}
//rowCount
int dataSize = data.size();
this.setRowCount(dataSize);
//paginate
if(dataSize > pageSize) {
try {
return data.subList(first, first + pageSize);
}
catch(IndexOutOfBoundsException e) {
return data.subList(first, first + (dataSize % pageSize));
}
}
else {
return data;
}
}
But when the table is loaded Next Buttons are not active because I am loading only those data required to load the first page. How can I Solve this.

Answer 1

You need to fire another query which sets the total rowcount. Basically, in LazyDataModel#load():
public List<StudyplanCategory> load(...) {
setRowCount(studyplanCategoryService.count());
return studyplanCategoryService.list(...);
}
Unrelated to the concrete problem, you should actually be using Query#setFirstResult() to set the first record index.