Question

Please advise that what is DTO pattern as I came from my analysis is that it is data transfer object pattern , Can you please advise any example of it in Hibernate specially or in any other java example, Thanks

Answer 1

A DTO is one of the work-arounds for the terrible persistence found in EJB 2.1 (collectively known as the Sun Blueprint Catalog). It is used for extracting data from a entity bean and passing it to the data layer. Data from that layer is placed in a DTO and put into the entity bean. This is only for bean managed persistence.

This is what was officially the meaning of a DTO. Today you also find this in transferring data from the back-end to the front-end (in client-server architecture).

If you want to use this in Hibernate, create a query/criteria for selecting the columns you need and then use the AliasToBeanResultTransformer for setting these columns in a DTO. An example in the Hibernate documentation:

List resultWithAliasedBean = 
    s.createCriteria(Enrolment.class)
        .createAlias("student", "st")
        .createAlias("course", "co")
        .setProjection(
            Projections.projectionList()
                add( Projections.property("co.description"), "courseDescription" )
        )
        .setResultTransformer( new AliasToBeanResultTransformer(StudentDTO.class) )
    .list();

StudentDTO dto = (StudentDTO)resultWithAliasedBean.get(0);