Spring and DAO w/ Annotation

Although EJB is moving forward to 3.0, and everyone seems to enjoy the POJO ORM stuff. I do miss some EJB 2.0 features. Particularly, being able to use the ejbSelect and finder methods! With xdoclet, one could easily annotate a method with its corresponding query.

/**
  * @ejb.select query="...."
  */
public abstract Collection ejbSelectWithKey(String key)
  throws FinderException;

Although it seems like named queries are to replace the use of this kind of methods. I still enjoyed the fact that the method is, afterall, a Java method. The Java language can provide name, parameter, and type checkings to this method, where named queries can't.

I could imaging something similar w/ Spring and DAO, and some simple AOP/proxy to achieve the following:

public abstract class PersonDAOHibernate implements PersonDAO
{
  @HQL("from Person p where p.id = :id");
  @InitializeProperties({"accounts", "projects"});
  public abstract Person getById(Long id)
    throws DataAccessException;
  @HQL("from Person p where p.age > 20");
  @Paged(pageSize = 10);
  public abstract Pager selectQualifiedAdults()
    throws DataAccessException;
  @HQL("from Person p where p.name like '%:name%'")
  @Paged(pageSize = 15);
  public abstract Pager selectByNameLike(String name)
    throws DataAccessException;
  @HQL(namedQuery="person.ageGreaterThan")
  @Paged
  public abstract Pager selectByAgeGreaterThanPaged(
    Integer age, int pageSize)
    throws DataAccessException;
  @HQL(namedQuery="person.ageGreaterThan")
  @PagedList
  public abstract List selectByAgeGreaterThanList(
    Integer age, int pageSize, int page)
    throws DataAccessException;
  @HQL(namedQuery="person.ageGreaterThan")
  @PagedList
  public abstract PagedList selectByAgeGreaterThanList(
    Integer age, int pageSize, int page)
    throws DataAccessException;
}

Different implementations can use different annotation for the queries e.g. @SQL, @EQL, etc. Not only can it embed a query, it can also link to named queries.

Without the Open Session In View pattern, it is necessary to load all the data that is required in upper tiers callers. There is a feature in XDoclet for EJB 2.0 to generate value objects that does this pretty well. However, in the recent development of ORM, it seems there is a need to manually initialize the lazily-loaded fields for each DAO methods (if not using Open Session In View). In this example, fields initialization can be explicitly specified using @InitializeProperties.

Lastly, when the query string and parameters are known, it can auto-magically create a Pager object, which can dynamically load a page of items when called.

Updated May 13, 2006 – See here