If you configure a polymorphic association to use proxies, this is what happens.
If you need to do a typecast, either:
(1) use outer-join="true" on the association OR (2) call session.load(Subtype.class, proxy.getId() ) to narrow the proxy type.
we can't possibly know a subtype w/o hitting the db.
jiesheng zhang wrote:
My problem is that I know one object is type A, but when I try to cast to A, I got a ClassCastException.
I have four classes in my cases: ContentDB,
ServerFileSysNode, InnerNode, and SharedFileSysNode. ServerFileSysNode(abstract)
InnerNode (concrete subclass of ServerFileSysNode,
may have an asscoaited SharedFileSysNode).
...(other subclass of ServerFileSysNode is omitted
here ).
ShareFileSysNode always associated with a ServerFileSysNode
ContentDB( a list of ServerFileSysNode, a list of
SharedFileSysNode).
Their mapping are shown at the bottom.
In my application initialization, I loaded all the
ServerFileSysNode and ShareFileSysNode in the ContentDB. However I found that if an InnerNode does
not have an associated SharedFileSysNode, the InnerNode will have a type of "InnerNode", that is
correct. Otherwise, it will have a type of "ServerFileSysNode$$EnhancedByCGLIB$$00", and the
"ServerFileSysNode$$EnhancedByCGLIB$$00" can not cast back to "InnerNode". I just wonder how the
hibernate decides that the object should be "ServerFileSysNode$$EnhancedByCGLIB$$00". Since
ServerFileSysNode is an abstract clas. In my database, there is no instance which is object of
"ServerFileSysNode"
Also I did not use the Session.load(Class, id) method to load the object explicitly. All the objects are loaded by association with the ContentDB.
Help is appreciated.
<?xml version="1.0" encoding="UTF-8"?> <hibernate-mapping>
<!-- map for ContentDB -->
<class name="ContentDB" table="deviceDB" proxy="contentDB">
<id name="id" column="dbID" type="long"
unsaved-value="0">
<generator class="sequence">
<param name="sequence">seq_resourceID</param>
</generator>
</id>
<set name="items" table="node" lazy="true"
inverse="true">
<key column="dbID"/>
<one-to-many class="ServerFileSysNode"/>
</set>
<set name="sharedFiles" table="sharedFiles"
lazy="true" inverse="true" cascade="save-update">
<key column="dbID"/>
<one-to-many class="SharedFileSysNode"/>
</set>
</class>
<!-- map for ServerFileSysNode -->
<class name="ServerFileSysNode" table="node"
discriminator-value='s' proxy="ServerFileSysNode">
<id name="id" column="fileID" type="long"
unsaved-value="0">
<generator class="sequence">
<param
name="sequence">seq_resourceID</param>
</generator>
</id>
<discriminator column="class" length="1"/>
<many-to-one name="database" column="dbId"
class="ContentDB" cascade="none"/>
<one-to-one name="persistShareProperty"
class="SharedFileSysNode"/>
<subclass name="InnerNode"
discriminator-value="i" proxy="InnerNode">
<!-- map goes here -->
</subclass>
</class>
<!-- map for the ShareFileSysNode -->
<class name="SharedFileSysNode" table="sharedFiles"
proxy="SharedFileSysNode" >
<id name="id" column="fileID" type="long"
unsaved-value="0">
<generator class="foreign">
<param name="property">hardNode</param>
</generator>
</id>
<one-to-one name="hardNode"
class="ServerFileSysNode" cascade="none"
constrained="true"/>
<many-to-one name="database" column="dbId"
class="ContentDB" cascade="none"/>
</class>
</hibernate-mapping>
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