[hibernate-dev] HHH-8999/HHH-10413 and Comparable IDs

[Gail Badner]

Missed something. Please see below...

On Wed, Mar 2, 2016 at 11:49 PM, Gail Badner <gbadner at redhat.com> wrote:

> ExecutableList#add attempts to keep track of whether the Executable
> objects are sorted. [1]
>
> Except for entity insert actions (which use InsertActionSorter),
> ExecutableList#add uses the following to determine if adding the current
> Executable to the end invalidates the sort:
>
> if ( previousLast != null && previousLast.compareTo( executable ) > 0 ) {
>     sorted = false;
> }
>
> EntityAction#compareTo compares the IDs for the current and previous
> EntityAction if they have different entity names; similarly,
> CollectionAction compares the collection keys for the current and previous
> CollectionAction if they have different entity names.
>
> In most cases, the ID class implements Comparable, although I don't know
> of any requirement that says this needs to be true.
>
> This breaks down when a byte[] ID is used as described by HHH-8999. The
> reason is that AbstractTypeDescriptor#comparator is null because it is
> assigned like this:
>
> this.comparator = Comparable.class.isAssignableFrom( type )
>         ? (Comparator<T>) ComparableComparator.INSTANCE
>         : null;
>
> PrimitiveByteArrayTypeDescriptor does not override
> AbstractTypeDescriptor#getComparator, so null is returned ultimately
> causing a NullPointerException in AbstractStandardBasicType#compare:
>
> public final int compare(Object x, Object y) {
>     return javaTypeDescriptor.getComparator().compare( (T) x, (T) y );
> }
>
> The same happens for PrimitiveCharacterArrayTypeDescriptor,
> ByteArrayTypeDescriptor, and CharacterArrayTypeDescriptor. Are there others?
>
> According to HHH-10413, this also affects version attributes.
>
> Here are a couple of alternatives:
>
> A) create comparators for PrimitiveCharacterArrayTypeDescriptor,
> ByteArrayTypeDescriptor, and CharacterArrayTypeDescriptor.
>

PrimitiveByteArrayTypeDescript should also be in the list for A).


>
>
> B) Change AbstractTypeDescriptor#comparator to:
>
> this.comparator = Comparable.class.isAssignableFrom( type )
>         ? (Comparator<T>) ComparableComparator.INSTANCE
>         : IncomparableComparator.INSTANCE;
>
> IncomparableComparator#compare always returns 0, so that comparison would
> never invalidate the sort.
>
>
B) is not acceptable for PrimitiveByteArrayTypeDescripter because a version
attribute can be of type byte[]. We definitely do not want all byte[]
version values to compare as equal. A Comparator needs to be implemented at
least for PrimitiveByteArrayTypeDescripter.

The following question only applies to
PrimitiveCharacterArrayTypeDescriptor, ByteArrayTypeDescriptor, and
CharacterArrayTypeDescriptor.


> Does it make sense to sort Executable objects by an ID or collection key
> that is an array? In other words, would such IDs be generated in a natural
> order? If not, I think B) makes more sense.
>

> Thoughts?
>
> Thanks,
> Gail
>
> [1]
> https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src/main/java/org/hibernate/engine/spi/ExecutableList.java#L194
>