We are migrating a legacy application to Hibernate that can dynamically alter tables at runtime to handle custom fields. Can anyone suggest how to extend Hibernate to support persisting these fields? Do we need to extend Hibernate classes (and is there a way to register these extensions?) or would custom EventListeners work somehow?

For example, the CustomPerson table looks like this when no custom fields are defined:



At runtime, additional columns might be added to store the custom fields



The (simplified) entity class looks like:



where the customFieldValues map will hold column names and there values for cf1, cf2, etc.

In addition, we need to support multiple databases with different custom tables via a single SessionFactory, so modifying the Configuration with new mappings at runtime (a la Support of Custom Fields with Hibernate) will not work.

Thanks in advance!
Noah

Hibernate version:
3.3.1

Name and version of the database you are using:
MySQL 5.0, SQL Server 2005

What does your database structure look like?

The table in question look like this before any custom fields have been added:



And like this after a couple fields have been defined:


Is that what you meant? Its the dynamic cf* columns that I need to dynamically map to a HashMap<columnName, columnValue>.

Thanks,
Noah

I actually use a similar type of mapping. It's easier if you stop looking at the custom fields as part of your first table because it's really not.

Just create 2 classes one for your Person Table and one for your Person Custom Field Tables. And you would use a one to many join.

@Entity
@Table(name = "customperson")
public class CustomPerson
{
@Id @GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer recNum;

@Version @Temporal(TemporalType.TIMESTAMP)
private Date lastUpdateTime;

@OneToOne @JoinColumn(name = "PersonId", unique = true)
private Person person;

@OneToMany(mappedBy="personId", fetch=FetchType.EAGER, targetEntity=PersonCustomFields.class)
private Set<PersonCustomField> People = new HashSet<PersonCustomField>();
}


I think that's what your looking for. You can use a map also, I just copied and pasted but the map would be a similar but you would use the @MapKey(name="personId") annotation.



@OneToMany(mappedBy="personId", fetch=FetchType.EAGER, targetEntity=PersonCustomFields.class)
@MapKey(name="personId")
private Map<Integer,PersonCustomField> People = new HashMap<Integer,PersonCustomField>();

Sorry, I think I wasn't clear about my table structure. The problem isn't joining the customperson table with the person table with a one-to-one relationship, but rather simply loading the data from the customperson table into the CustomPerson entity.

The problem I have with creating a Hibernate mapping for the "customperson" table is that I don't know at design-time what columns it will have. At runtime, any number of columns may get added to the table (through ALTER TABLE statements). It's these columns that I want to store in a HashMap that holds column names and column values, but Hibernate cannot by default handle that situation.

Any other ideas about how to load and save a dynamic (i.e. unmapped) set of columns?

Thanks,
Noah

You could use the same types of mappings I described above but in your Person Class just add the getters and setters to access or find the value in the one to many list/map/set(whatever you decide on)

Then mark those getters and setters as @Transient

For instance

@Transient
public String getCustomField01(){
//put code to get customField01 from the PersonCustomFields collection here
}