Pagination Issue while join in Hibernate Criteria

Question

I want to have the pagination after the multiple table join in criteria.

The issue is:

The duplicate records generated when I join the tables. The pagination applied to the record set(With duplication).

I use this criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY); to remove the duplicated records.

For example: Normally I got 10 records after applying the removing duplication. When I set my start index as 1 and end index as 5 , I am supposed to get 5 records but it returns 2 or 3(approx). It depends on the joining.

Please help me out.

Answer 1

The problem here is in the two different techniques beeing applied.

• Firstly there is a pagination correctly applied on the DB Server. It will return the intended number of rows (e.g. 5).
• The second part is the Application part, where the Hibernate does select DISTINCT values from these 5 records.

So if there are in fact 2 rows doubled plus 1 other, the transformation will result in 3 objects.

The correct (and maybe the best) way, how to avoid that, is to not use fetching of the collections. If we need collection to be displayed, we should load it lazily (e.g. using batch-size to reduce number of selects)

If we need collection to be used as a filter, we should convert it into subquery, and again do the pagination on the root entity, with the IN (Subquery) clause in place

Imagine this, Parent table:

ParentId, Code
1       , 'P1' 
2       , 'P2'
3       , 'P3'

The child table:

ChildId , Code , ParentId
1       , 'C1' , 1
2       , 'C2' , 1
3       , 'C3' , 2
4       , 'C4' , 2
5       , 'C5' , 3

If we will ask for a Parent and also join the Child collection, we will

1. recieve 5 rows on the DB server,
2. which will be converted into only 3 Distinct Parent objects on the Application level

Answer 2

I answered this here: Pagination with Hibernate Criteria and DISTINCT_ROOT_ENTITY

You need to do 3 things, 1) get the total count, 2) get the ids of the rows you want, and then 3) get your data for the ids found in step 2. It is really not all that bad once you get the order correct, and you can even create a generic method and send it a detached criteria object to make it more abstract.