Hi all,
I'm currently working on a legacy system. The DB has a lot of columns where
null should actually be allowed, but instead those fields are non-nullable and
get other values (empty string, "0", "-1" etc) written to them to indicate the
absence of a value. Yay.
Unfortunately I can't just do the right thing; make the fields nullable and
start writing nulls, since that would make other (non Cayenne) parts of the
system explode, so I have to create a temporary workaround while I work through
each column and make it nullable and fix (or kill) the legacy apps.
What I'd like to do is write my application logic as if the column was
nullable, setting nulls when I want to, but when the object goes to the DB,
"legacy nulls" are written to the DB instead (empty string or "-1" or whatever).
I have a working solution, I just wanted to check if you guys would have a
better or more performant solution or see anything potentially wrong with what
I'm doing.
What I'm doing is creating an interface (HasFictionalNullValues) which can be
implemented by entity classes that require it. It defines a single method that
can be implemented like…
public class SomeEntityClass extends _SomeEntityClass implements
HasFictionalNullValues {
@Override
Map<Property,Object> fictionalNullValues) {
Map<Property,Object map = new HashMap<>();
map.put( NAME, "" );
map.put( AGE, -1 );
return map;
}
[...rest of class body...]
}
…then I add a listener to my DataDomain to catch new and updated objects
public class FictionalNullValuesListener {
@PrePersist( { BaseDataObject.class } )
@PreUpdate( { BaseDataObject.class } )
public void onPrePersist( BaseDataObject object ) {
if( object instanceof HasFictionalNullValues ) {
((HasFictionalNullValues)object).fictionalNullValues().forEach( ( property,
replacementNullValue ) -> {
if( property.getFrom( object ) == null ) {
property.setIn( object,
replacementNullValue );
}
} );
}
}
}
Any comments on this practice or something I'm missing?
Cheers,
- hugi
