Creating Mappings with Hibernate XML Files - Beginning Hibernate: From Novice to Professional - page 145

Attribute Values Default Description

optimistic-lock none , version version

Specifies the optimistic locking dirty ,
all strategy to use. The strategy applies
at a class level, but in Hibernate 3 can
also be specified (or overridden) at an
attribute level. Optimistic locking is dis-
cussed in Appendix A.

persister

Allows a custom ClassPersister object
to be used when persisting the entity.

polymorphism implicit , explicit implicit

Determines how polymorphism is to be
used. The default implicit behavior will
return instances of the class if super-
classes or implemented interfaces are
named in the query, and will return
subclasses if the class itself is named in
the query.

proxy Specifies a class or an interface to use as

the proxy for lazy initialization. Hiber-
nate uses runtime-generated proxies by
default, but you can specify your own
implementation of org.hibernate.
HibernateProxy in their place.

rowid

Flags that row IDs should be used (a
database-implementation detail allow-
ing Hibernate to optimize updates).

schema

Optionally overrides the schema speci-
fied by the <hibernate-mapping> element.

select-before- true , false false

Flags that Hibernate should carry out

update extra work to avoid issuing unnecessary

UPDATE statements. If set to true , Hiber-
nate issues a SELECT statement before
attempting to issue an UPDATE statement
in order to ensure that the UPDATE state-
ment is actually required (i.e., that col-
umns have been modified). While this is
likely to be less efficient, it can prevent
database triggers from being invoked
unnecessarily.

subselect A subselection of the contents of the

underlying table. A class can only use
a subselect if it is immutable and read-
only (because the SQL defined here can-
not be reversed). Generally, the use of a
database view is preferable.

table The table name associated with the class

(if unspecified, the unqualified class
name will be used).

where

An arbitrary SQL where condition to be
used when retrieving objects of this class
from the table.

Many of these attributes in the <class> element are designed to support preexisting data-
base schemas. In practice, the name attribute is very often the only one set.