How to persist an entity from an non-entity subclass in Hibernate

Question

I am trying to extend an entity into a non-entity which is used to fill the superclass's fields. The problem is that when I try to save it Hibernate throws a MappingException. This is because even though I cast ReportParser to Report, the runtime instance is still a ReportParser so Hibernate complains that it is an unknown entity.

@Entity
@Table(name = "TB_Reports")
public class Report
{
   Long id;
   String name;
   String value;

   @Id
   @GeneratedValue
   @Column(name = "cReportID")
   public Long getId()
   {
      return this.id;
   }

   public void setId(Long id)
   {
      this.id = id;
   }

   @Column(name = "cCompanyName")
   public String getname()
   {
      return this.name;
   }

   public void setName(String name)
   {
      this.name = name;
   }

   @Column(name = "cCompanyValue")
   public String getValue()
   {
      return this.name;
   }

   public void setValue(String value)
   {
      this.value = value;
   }
}

ReportParser is only used to fill in fields.

public class ReportParser extends report
{
   public void setName(String htmlstring)
   {
      ...
   }

   public void setValue(String htmlstring)
   {
      ...
   }
}

Attempt to cast it to a Report and save it

...
ReportParser rp = new ReportParser();
rp.setName(unparsed_string);
rp.setValue(unparsed_string);
Report r = (Report)rp;
this.dao.saveReport(r);

I've used this pattern before I moved to an ORM, but I can't figure out how to do this with Hibernate. Is it possible?

Answer 1

Is it absolutely necessary to subclass the entity? You could use the builder pattern:

public class ReportBuilder {
    private Report report;
    public ReportBuilder() {
        this.report = new Report();
    }
    public ReportBuilder setName(String unparsedString) {
        // do the parsing
        report.setName(parsedString);
        return this;
    }
    public ReportBuilder setValue(String unparsedString) {
        // do the parsing
        report.setValue(parsedString);
        return this;
    }
    public Report build() {
        return report;
    }
}

Report report = new ReportBuilder()
                   .setName(unparsedString)
                   .setValue(unparsedString)
                   .build();
dao.saveReport(report);