Hi Andy,
Thanks for your thoughtful insights here.
It appears we are in sync for supporting field types of Object as
FCO, and now we're discussing support for Object as SCO (embedded).
On Aug 17, 2005, at 11:26 PM, Andy Jefferson wrote:
Hi Craig,
Well we interpret all types as serialized="false", but in section
18.14 of the
spec "java.lang" types (which Object is) are to be
embedded="true" by
default. So we interpret this as serialising the Object into the
table of the
class, into a BLOB column.
I tried to be more explicit about this in the Proposed Final Draft,
to say that embedded="true" doesn't mean serialized but embedded
column by column. Just like embedded PC instances.
OK, but the issue here is whether "java.lang.Object" defaults to
embedded="true" or embedded="false". The wording at the start of
the section
18.14 Embedded can be interpreted 2 ways. That java.lang.Object is
embedded
by default, or it isn't.
I've enhanced the spec as follows:
The embedded attribute specifies whether the field should be stored
as part of the containing instance instead of as its own instance in
the datastore. It must be specified or default to "true" for fields
of primitive types, wrappers, java.lang, java.math, java.util,
collection, map, and array types specified above; and “false” for
other types including persistence-capable types, interface types and
the Object type.
Looking at some of the JDO1 books, Object is *not* embedded by
default, so
I've updated JPOX to reflect this (in last nights build -
18/08/2005). This
gets around the immediate issue that Michelle raised.
This is consistent with what the spec intended.
When we have an Object field that is marked as embedded="true" JPOX
will
currently serialise it into a single column - since we don't support
embedding it column by column into the owning table.
Embedded is different from serialized. I've proposed a spec change to
that effect. I think that people would be surprised to find embedded
objects were actually serialized in this case, as embedded PC types
like Address are handled very differently elsewhere in the spec
(using the <embedded> element).
I looked at the PFD and
couldn't decide if this is valid or not. You're saying that we
should embed
the Object column-by-column.
We have 2 situations
<field name="myObjectField" embedded="true"/>
This one we treat as serialised currently since no embedded
definition is
available
<field name="myObjectField">
<embedded>
...
</embedded>
</field>
This we do not support since the Object field could have multiple
"implementations" stored there, so the fields will vary. For the
same reason
we don't support the same situations with interface fields
The spec doesn't call out whether support for embedded Object or
embedded interfaces is required. I don't think it should be required,
but then we need a way to identify an implementation as supporting
this feature. Something like
javax.jdo.options.mapping.EmbeddedInterface and ...EmbeddedObject.
Craig
--
Andy
Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!
