Werner,
You must be correct. I thought that option model just has to know which question it
belongs to.
Can you explain what happens after the question.setAnswer(B) is invoked? On the option
model sides, A, B and C are all the same, but why only A is removed, B can be got from
both question.option and question.answer?
What will you do in my situation? How can I mark the correct answer of a question?
Thanks,
Sean
----- Original Message -----
From: "Werner Guttmann" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Thursday, June 17, 2004 6:28 PM
Subject: Re: [castor-user] [JDO] A collection and an object refer to the same type
>
> Sean,
>
> I guess your problems are a direct consequence of not modelling the relations
> correctly. In your example, you have two relations, a 1:1 (question -
> answer) and a 1:M relation (question - options). As far as the entity model.Question
> is concerned, you are fine as you have defined both relations,
> indeed.
>
> But on the model side of things, you've defined only one member named 'question'. Is
> this the return leg of the question - answer or questions - options
> relation ?
>
> I guess you see what I mean ...
>
> Werner
>
> On Thu, 17 Jun 2004 14:25:15 +0800, Sean Liang wrote:
>
> >Please take a look at the following snippet:
> >
> > <class identity="id" key-generator="HIGH-LOW" name="model.Question">
> > <map-to xml="question" table="question" />
> > <field name="id" type="integer">
> > <sql name="id" type="integer" />
> > </field>
> > <field name="subject" type="string">
> > <sql name="subject" type="varchar" />
> > </field>
> > <field name="option" type="model.Option" collection="collection">
> > <sql many-key="question" />
> > </field>
> > <field name="answer" type="model.Option">
> > <sql name="answer" />
> > </field>
> > </class>
> >
> > <class identity="id" key-generator="HIGH-LOW" name="model.Option">
> > <map-to xml="questionoption" table="questionoption" />
> > <field name="id" type="integer">
> > <sql name="id" type="integer" />
> > </field>
> > <field name="question" type="model.Question">
> > <sql name="question" />
> > </field>
> > <field name="value" type="string">
> > <sql name="value" type="varchar" />
> > </field>
> > </class>
> >
> >As what you can see, a Question contains several possible options, one of which is
> >the correct answer. That is, option and answer in the Question
> refer to the same type "model.Option".
> >
> >Let's say we have a question with 3 options A, B, C.
> >
> >The first time I call question.setAnswer(A), it is totally fine. But the next time
> >I call question.setAnswer(B), guess what? Option A is removed from
> question.option collection and in the database A.question is set to null.
> >
> >I tried this stupid code:
> >
> > Option a = question.getAnswer();
> > question.setAnswer(b);
> > a.setQuestion(question);
> >
> >but it still doesn't work. I don't have idea about how to solve this problem now.
> >
> >Could you provide me any suggestion for that? Thanks in advance.
> >
> >Sean
>
>
>
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