Re: [Jaxor-devel] Re: Associating Lists

[Carl F. <car...@gm...>]

I think I see why you have avoided this for so long... it is hard to
know exactly what the user is going to want without resorting to the
verbose hibernate style dtd. I am trying to avoid changing the DTD at
all costs and trying to use the api as it exists to achieve the
results we are looking for. The main problem I continue to run into is
that of id generation and other things of that nature (filling in
details of a linking table that don't neccessarily have anything to do
with the links).

Forgetting about the linking table details I would like to throw a
theory out there.  Please tell me if this holds water.



If there are entity ref's to multiple tables, the host table can be
thought of as a many to many linking table of some kind.

IE groupmembers has two entity ref's, one to groups, one to users.
This means jaxor should generate a newInstances(group, userList) and a
newInstances(user, groupList) method in the Finder. This is the easy
case.

Now, lets look at adding a third entity ref.  I couldn't figure out a
sensible way to model this with users and groups so I am gonna go with
the structure of XML.  Say we wanted to create a generic way to store
XML in an RDBMS. We would have tables for documents, elements and
attributes. If this was normalized we would only want one instance for
each element and attribute. So if we go all the way down to the
instance of an attribute we would have something like this:

<jaxor package="net.sourceforge.jaxor.example.xml.jaxor">
    <entity name="attribute_instance" alias="AttributeInstance" >
        <primary-key>
            <column name="attribute_instance_id" type="Long"/>
        </primary-key>
        <column name="element_instance_id" type="Long"/>
        <column name="attribute_id" type="Long"/>
        <column name="document_id" type="Long"/>

        <entity-ref table="element_instance">
            <key source="element_instance_id" target="element_instance_id"/>
        </entity-ref>
        <entity-ref table="attribute">
            <key source="attribute_id" target="attribute_id"/>
        </entity-ref>
        <entity-ref table="document">
            <key source="document_id" target="document_id"/>
        </entity-ref>

    </entity>
</jaxor>

The attribute instance points to a singular element instance, which in
turns points to a concrete element. The attribute instance also points
to a concrete attribute and document.

In this case, we would want jaxor to generate a bunch of
newInstances() methods....  We are only going to want three:

newInstances(document, attribute, elementInstanceList)
newInstances(document, attributeList, elementInstance)
newInstances(documentList, attribute, elementInstance)

I don't think it really makes sense to pass in more than one List.

Of course it is completely plausible to have a List of groups and a
List of users and you want to put all of the users into all of the
groups, but does that hold true when you have more than two
references?

newInstances(documentList, attribute, elementInstance)
newInstances(document, attributeList, elementInstance)
newInstances(document, attribute, elementInstanceList)

newInstances(document, attributeList, elementInstanceList)
newInstances(documentList, attribute, elementInstanceList)

newInstances(documentList, attributeList, elementInstance)

newInstances(documentList, attributeList, elementInstanceList)

The matrix only grows if we add another entity ref. Not to mention we
still don't have a way to fill in the id's of all of the rows that
will be created...

Does this make sense, and should I move forward with this strategy?