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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