Seimos

Hibernate Criteria Encapsulation

Seimos is not a Hibernate substitute but an extension. It encapsulates repetitives issues when programming through Criteria. Here you are some examples:

1. Full list

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1.1. Criteria

Criteria criteria = session.createCriteria(Cat.class);    
List cats = criteria.list();

1.2. Seimos

List cats = dao.list();

2. Adding restrictions

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2.1. Criteria

Criteria criteria = session.createCriteria(Cat.class);
criteria.add(Restrictions.eq(“id”, 10000));
List cats = criteria.list();

2.2. Seimos

Filters filters = new Filters();
filters.add(new Filter(“id”, 10000));
List cats = dao.find(filters);

Of course both Criteria and Seimos have a lot of restrictions type. For Seimos each new Filter added to filters could use a specific condition for filtering. For example, new Filter's could be used as follows:

filters.add(new Filter("description", "Pap"));
filters.add(new Filter("birth", new Date()));
filters.add(new Filter("serial", 10000, Condition.GREATER);  // Serial for cats? It's just an example :)

And Condition could be any of

• EQUALS
• NOT_EQUALS
• STARTS_WITH
• NOT_STARTS_WITH
• ENDS_WITH
• NOT_ENDS_WITH
• EQUALS_CASE_INSENSITIVE
• STARTS_WITH_CASE_SENSITIVE
• NOT_STARTS_WITH_CASE_SENSITIVE
• ENDS_WITH_CASE_SENSITIVE
• NOT_ENDS_WITH_CASE_SENSITIVE
• GREATER
• GREATER_OR_EQUALS
• LESS
• LESS_OR_EQUALS
• NULL
• NOT_NULL
• BETWEEN
• OR
• AND
• IN
• NOT_IN
• EQ_PROPERTY
• LESS_THAN_PROPERTY
• LESS_OR_EQUALS_THAN_PROPERTY
• GREATER_THAN_PROPERTY
• GREATER_OR_EQUALS_THAN_PROPERTY

For default, any search for an attribute of String type use MatchMode.START and 'like' clausule when Condition is supressed, i.e., new Filter("description", "Pap") it's the same of new Filter("description", "Pap", Condition.STARTS_WITH). For any other type, default condition is EQUALS, that means, new Filter("id", 10000) it's the same of new Filter("id", 10000, Condition.EQUALS).

Filter's can be nested when Condition allows. Condition.AND and Condition.OR use constructor

new Filter(Condition.AND, filter01, filter02)
new Filter(Condition.OR, filter01, filter02)

filter01 and filter02 are new Filter(...) of any type, including with Condition.AND or Condition.OR

3. Sorting

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3.1. Criteria

Criteria criteria = session.createCriteria(Cat.class);
criteria.add(Restrictions.like(“description”, “Pap”)
  .addOrder(Order.asc(“description”);
List cats = criteria.list();

3.2. Seimos

Filters filters = new Filters();
filters.add(new Filters(“description”, “Pap”)
  .add(new Filter(“description”, Order.ASC));
List cats = dao.find(filters);

More Filter's with Order.ASC or Order.DESC can be added to filters.

4. Pagination

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4.1. Criteria

Criteria criteria = session.createCriteria(Cat.class);
criteria.add(Restrictions.like(“description”, “Pap”)
  .addOrder(Order.asc(“description”)
  .setFirstResult(101)
  .setMaxResult(10);
List cats = criteria.list();

4.2. Seimos

Filters filters = new Filters();
filters.add(new Filters(“description”, “Pap”)
  .add(new Filter(“description”, Order.ASC));
List cats = dao.find(filters, 101, 10);

5. Associations

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Till now there's not great difference between Criteria and Seimos. But when using associations Seimos can help avoid a lot of code lines.

5.1. Criteria

Criteria criteria = session.createCriteria(Cat.class);
criteria.add(Restrictions.like(“description”, “Pap”)
  .addOrder(Order.asc(“description”)
  .setFirstResult(101)
  .setMaxResult(10);
  
Criteria subCriteria = criteria.createCriteria("kind", "kind");
subCriteria.add(Restrictions.eq("description", "description"));

List cats = criteria.list();  

For deep association in more than one level another subCriteria is needed.

Criteria criteria = session.createCriteria(Cat.class);
criteria.add(Restrictions.like(“description”, “Pap”)
  .addOrder(Order.asc(“description”)
  .setFirstResult(101)
  .setMaxResult(10);
  
Criteria subCriteria = criteria.createCriteria("kind", "kind");
subCriteria.add(Restrictions.eq("description", "persa"));

Criteria anotherSubCriteria = subCriteria.createCriteria("anAssociation", "anAssociation");
anotherSubCriteria.add(Restrictions.eq("attribute", "anything"));

/* ... and so on */

List cats = criteria.list();  

5.2. Seimos

Filters filters = new Filters();
filters.add(new Filters(“description”, “Pap”)
  .add(new Filter(“description”, Order.ASC))
  .add(new Filter("kind.description", "persa"))
  .add(new Filter("kind.anAssociation.attribute", "anything"));
List cats = dao.find(filters, 101, 10);

Seimos can either define JoinType when adding a Filter with association.

  .add(new Filter("kind.description", "persa", JoinType.LEFT_OUTER_JOIN))

6. Transforming results

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Criteria results naturally fetchs a list of Objects but can also being transformed. Of course, in most cases, is necessary use a particular domain, DTO, VO, table mapping, bean or whatever. Criteria has an appropriate transformer for this cases.

6.1. Criteria

Criteria criteria = session.createCriteria(Cat.class);
criteria.add(Restrictions.like(“description”, “Pap”)
  .addOrder(Order.asc(“description”)
  .setFirstResult(101)
  .setMaxResult(10);
  
Criteria subCriteria = criteria.createCriteria("kind", "kind");
subCriteria.add(Restrictions.eq("description", "persa"));

Criteria anotherSubCriteria = subCriteria.createCriteria("anAssociation", "anAssociation");
anotherSubCriteria.add(Restrictions.eq("attribute", "anything"));

/* ... and so on */

criteria.setResultTransformer(new AliasToBeanResultTransformer(Cat.class));

List cats = criteria.list();  

Hibernate has some transformers in its package. AliasToBeanResultTransformer above helps Criteria to fetch results within a list of Cat's. But when Cat have an association with another bean, AliasToBeanResultTransformer is not able to transform.

6.2. Seimos

The same code in 5.2 already embed a transformer for fetching a list of Cat's. Thus, List can be strongly typed.

Filters filters = new Filters();
filters.add(new Filters(“description”, “Pap”)
  .add(new Filter(“description”, Order.ASC))
  .add(new Filter("kind.description", "persa"))
  .add(new Filter("kind.anAssociation.attribute", "anything"));
List<Cat> cats = dao.find(filters, 101, 10);

7. Projections

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Even narrowing results with Restrictions, Criteria.list() fetchs a greedy collection with all model attributes. Hibernate provides Projections to define which attributes are finally projected or selected.

7.1. Criteria

Criteria criteria = session.createCriteria(Cat.class);
criteria.add(Restrictions.like(“description”, “Pap”)
  .addOrder(Order.asc(“description”)
  .setFirstResult(101)
  .setMaxResult(10);
  
Criteria subCriteria = criteria.createCriteria("kind", "kind");
subCriteria.add(Restrictions.eq("description", "persa"));

Criteria anotherSubCriteria = subCriteria.createCriteria("anAssociation", "anAssociation");
anotherSubCriteria.add(Restrictions.eq("attribute", "anything"));

criteria.setResultTransformer(new AliasToBeanResultTransformer(Cat.class));

/* is something missing here? */

criteria.setProjections(Projections.projectionList()
  .add(Projections.alias(Projections.property(“id”), “id”))
  .add(Projections.alias(Projections.property(“kind.id”, “kind.id”))
  .add(Projections.alias(Projections.property(“kind.anAssocation.description”, “kind.anAssociation.description”))

List cats = criteria.list();  

Running this code, criteria.list() would throw an exception indicating that 'anAssociation.description' is not an attrbute of 'kind'. It's lacking some aliases before. The real code should be:

Criteria criteria = session.createCriteria(Cat.class);
criteria.add(Restrictions.like(“description”, “Pap”)
  .addOrder(Order.asc(“description”)
  .setFirstResult(101)
  .setMaxResult(10);
  
Criteria subCriteria = criteria.createCriteria("kind", "kind");
subCriteria.add(Restrictions.eq("description", "persa"));

Criteria anotherSubCriteria = subCriteria.createCriteria("anAssociation", "anAssociation");
anotherSubCriteria.add(Restrictions.eq("attribute", "anything"));

criteria.setResultTransformer(new AliasToBeanResultTransformer(Cat.class));

criteria.crateAlias(“kind.anAssociation”, “kind_anAssociation”);

criteria.setProjections(Projections.projectionList()
  .add(Projections.alias(Projections.property(“id”), “id”))
  .add(Projections.alias(Projections.property(“kind.id”, “kind.id”))
  .add(Projections.alias(Projections.property(“kind.anAssocation.attribute”, “kind.anAssociation.attribute”))

List cats = criteria.list();  

7.2. Seimos

Just as it was at 6.2. All aliases needed are created.

Filters filters = new Filters();
filters.add(new Filters(“description”, “Pap”)
  .add(new Filter(“description”, Order.ASC))
  .add(new Filter("kind.description", "persa"))
  .add(new Filter("kind.anAssociation.attribute", "anything"));
List<Cat> cats = dao.find(filters, 101, 10);

Filter allows programmer to choose if she needs a projection or just a clausule for filtering. Below, an example if 'id' is used as 'where' clausule but it's not projected.

Filters filters = new Filters();
filters.add(new Filters(“description”, “Pap”)
  .add(new Filter("id", 10000, Projection.NO))
  .add(new Filter(“description”, Order.ASC))
  .add(new Filter("kind.description", "persa"))
  .add(new Filter("kind.anAssociation.attribute", "anything"));
List<Cat> cats = dao.find(filters, 101, 10);

Another feature for help adding many attributes is using wildcards and regex in Filter.

Filters filters = new Filters();
filters.add(new Filters(“description”, “Pap”)
  .add(new Filter("id", 10000, Projection.NO))
  .add(new Filter("at*", WildCard.YES))   // adds all attributes that matches with 'at*' regex
  .add(new Filter(“description”, Order.ASC))
  .add(new Filter("kind.description", "persa"))
  .add(new Filter("kind.anAssociation.attribute", "anything"));
List<Cat> cats = dao.find(filters, 101, 10);

This last features is really good for adding all attributes of a model. For this, a special WildCard was created.

Filters filters = new Filters();
filters.add(new Filters(“description”, “Pap”)
  .add(new Filter("id", 10000, Projection.NO))
  .add(new Filter("*", WildCard.YES))   // adds all attributes of Cat. Same of new Filter(".*", WildCard.YES)
  .add(new Filter(“description”, Order.ASC))
  .add(new Filter("kind.description", "persa"))
  .add(new Filter("kind.anAssociation.attribute", "anything"));
List<Cat> cats = dao.find(filters, 101, 10);

8. Grouping

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Grouping a query is necessary when some agregation is used.

// TODO

9. Setings

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If you read until here perharps have notices that in Seimos 'dao' is never initialized. Seimos provides some generics classes to help use of Filter and embeds most used CRUD operations.

For use it for Cat.class filtering, a CatDao interface and CatDaoImpl must be used in associations with that generics classes.

public interface CatDao extends GenericDao<Cat> { /* ... */ }

@Repository
public class CatDaoImpl extends GenericDaoImpl<Cat> implements CatDao { /* ... */ }

Most cases need also of a service or manager layer, and Seimos helps it either.

public interface CatService extends GenericService<Cat> { /* ... */ }

@Service
public class CatServiceImpl extends GenericServiceImpl<Cat, CatDao> implements CatService {

  @Autowired
  public CatDao catDao;
  
  @Override
  public CatDao getDao() {
    return catDao;
  }

  /* ... */
}

For each implementation, methods create, find, update and remove are provided. Only if its behaviour is not default, they are overrided.