Help needed on converting legacy code to Hibernate

greenbee · **Joined:** Mon Mar 17, 2008 2:50 pm **Posts:** 24

I am converting an application that was written in good old JDK 1.3 days to use Hibernate and I need a helping hand on two issues:
1. My object contains a HashMap of various properties. These properties are stored in the separate table with the following structure:

Code:

create table DOC_PROPS (
   DOC_ID               integer                        not null,
   PROP_NAME            varchar(32)                    not null,
   PROP_TYPE            char(1)                        default 'A' not null
         constraint CKC_PROP_TYPE check (PROP_TYPE in ('A','I','D','F')),
   PROP_VALUE           varchar(60)                    null,
   constraint PK_DOC_PROPS primary key (DOC_ID, PROP_NAME)
)

Where PROP_TYPE value defines the type of the property:

A - alphanumeric (String);

I - Integer;

D - Date;

F - Float;Now in my hibernate mapping I am writing:

Code:

<class name="Document" ... >
    <property .../>
    ...
    <map name="documentProps" table="DOC_PROPS">
        <key column="DOC_ID"/>
        <map-key column="PROP_NAME" type="string"/>
        <element ??????? - here I stuck />
    </map>
</class>

Can someone suggest how to tell hibernate to convert varchar into proper object type based on PROP_TYPE value?

2. The second problem is that legacy Java code for the Document class does not have numeric surrogate key that exists in the database.
Do I have to specify <id> construct in the mapping file? I did put there <composit-id> for the natural key corresponding to the unique DB constraint. All references in the database, however are done via surrogate key.

gonzao_diaz · **Joined:** Mon Nov 26, 2007 2:29 pm **Posts:** 443

Create class containing prop_name, prop_type and prop_value, and map it as a component, using the composite-element tag.

There is an example in the documentation, 8.2. Collections of dependent objects

greenbee · **Joined:** Mon Mar 17, 2008 2:50 pm **Posts:** 24

gonzao_diaz wrote:

Create class containing prop_name, prop_type and prop_value, and map it as a component, using the composite-element tag.

There is an example in the documentation, 8.2. Collections of dependent objects

Unfortunately, it is not what I need, unless I want to rewrite the business logic, which I do not.
I don't need a composite-element with a special class for it.
My element must be an object of java.lang.String, java.lang.Integer, java.lang.Float or java.util.Date and nothing else.

Somehow I have to make Hibernate dynamically change the 'type' of the element based on prop_type value. I need a special case of mapping a database row to the Map.Entry instance.
I was thinking in the lines of utilizing the <meta> but not sure how to do it.

opearce · **Joined:** Fri Jul 14, 2006 12:05 pm **Posts:** 19

I'd create a UserType. The sqlTypes() method would return an array containing 2 copies of Types.VARCHAR. The returnedClass() method would just return Object.class. The nullSafeSet() and nullSafeGet() methods would need to deal with the prop_type and prop_value columns and handle them appropriately.

Hope this helps,
Oscar

greenbee · **Joined:** Mon Mar 17, 2008 2:50 pm **Posts:** 24

opearce wrote:

I'd create a UserType. The sqlTypes() method would return an array containing 2 copies of Types.VARCHAR. The returnedClass() method would just return Object.class. The nullSafeSet() and nullSafeGet() methods would need to deal with the prop_type and prop_value columns and handle them appropriately.

Hope this helps,
Oscar

I'll try that approach, although, it does look quite complicated - 11 methods to implement for the UserType class. Never done it before. Methods you mentioned are easy. I am more concerned with assemble/disassemble methods.

opearce · **Joined:** Fri Jul 14, 2006 12:05 pm **Posts:** 19

Actually, they can just delegate to deepCopy, something like this:

Code:

public Object deepCopy(Object value) {
  if (value instanceof Date) {
    // Date is mutable, so return a new Date
    return new Date(((Date) value).getTime());
  } else {
    // the other types are not mutable, so just return them
    return value;
  }
}

public Serializable disassemble(Object value) throws HibernateException {
  return (Serializable) deepCopy(value);
}

public Object assemble(Serializable cached, Object owner) throws HibernateException {
  return deepCopy(cached);
}

greenbee · **Joined:** Mon Mar 17, 2008 2:50 pm **Posts:** 24

Thank yo.