Introduction

Hibernate Criteria Extension (HCE) is a extension library for hibernate, HCE is not a substitution of hibernate.

HCE Architecture :

HCE can dynamically detect an association join through hibernate annotation configuration.

One of the powerful feature of HCE is association return value. e.g :

• Hibernate Criteria

Actually, when we select animal, it's country will be fetched automatically as the fetch type is EAGER. However, when we have a large of object and the projections declaration is needed for keeping performance. We must override the fetch type by using criteria, hql, or sql query. We will use criteria for the example.

Code :

DetachedCriteria detachedCriteria = DetachedCriteria.forClass(Animal.class, "animal");

detachedCriteria.createAlias("animal.country", "country");

detachedCriteria.setProjection(Projections.projectionList()

.add(Projections.property("animal.id"))

.add(Projections.property("animal.name"))

.add(Projections.property("country.name"))

);

Unfortunately, the code above throw an exception : java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to Animal.

Hibernate cannot return an association selected field when using projections. In this case, we select “country.name” and hibernate cannot set the value of name to country. We need to declare new property and give alias for “country.name”. This will happened to every associated projections.

• HCE Query

Code :

DetachedCriteria detachedCriteria = criteriaWithProjections(new String[] {"id", "name", "country.name"});

The sql query will be looked like :

select

this_.id as y0_,

this_.name as y1_,

country0x1_.name as y2_

from

Animal this_

inner join

country country0x1_

on this_.countryId=country0x1_.id

The example result will be looked like : Animal@40e99ce5[id=1,name=Panda,numberOfFeet=0,food=<null>,description=<null>,country=softtech.hong.hce.junit.model.Country@9706da8[id=<null>,code=<null>,name=China,description=<null>,shortname=<null>,active=false,cities=<null>]]

 

Hibernate Criteria Extension (HCE) is written to solve hibernate limitation. HCE can simplify your code. HCE API can let you to select part of columns that you need, we just give the field names that we want to select. HCE support for association and automatically detect join type from entity mapping. HCE is written based on hibernate criteria and projections.

HCE offer you a better way to generate query script without spend too much time. HCE give you a simple way to declare select, restriction, and order.

HCE’s goal is to relieve developer a better way to select columns without ignore the performance issue. HCE may not be the best solution for every conditions. However, HCE can certainly help you to simplify projections declaration, restrictions with association, and order.

Why Hibernate Criteria Extension (HCE) ?

HCE give us some reasons on why it should be used :

• I suggest that we should get the data only that we need. Although for this time there is not performance issue when selecting a table, we have never know for future if it still make sense for us to get all the column data at one time that we don't need all of them absolutely (not every field is used). In Hibernate, we can use projections. Using projections need more code to do.

• Let hibernate select all columns in a entity causing debug problem. We will be confused if we only want to track one column value. We need to substract the query generated before copy and paste to database browser.

• Using criteria and projections prevent n+1 select problem. By using HCE and give the projections, we will override the default configuration of hibernate, the columns to be selected is chosen well.

• The less code you write, the less time you need to build an application. By using HCE, I hope we reduce to write method. We can use one method for many solutions.
  
  
  
  HCE Repository :
  hce-hibernate3x => https://github.com/kismanhong/hce
  hce-hibernate4x => https://github.com/kismanhong/hce-hibernate4x
  
  
  HCE documentation can be seen from http://plihplih.com/hce/hce.pdf and You can see the API at http://plihplih.com/hce