Re: Question about flatten relationship

From: xuzhou (xuzho..oftHome.net)
Date: Sun Nov 24 2002 - 21:04:18 EST

  • Next message: Craig Miskell: "Re: Question about flatten relationship"

    Hi Craig,

    Thanks for your reply.

    I built the relationship as you described. Please examine my attachement.

    Regards,
    Xuzhou

    ----- Original Message -----
    From: "Craig Miskell" <cmiskell@albatross.co.nz>
    To: "xuzhou" <xuzhou@SoftHome.net>
    Cc: <cayenne-devel@objectstyle.org>
    Sent: Saturday, November 23, 2002 10:23 AM
    Subject: Re: Question about flatten relationship


    > Hi,
    > In the case that the relationship is across a many-to-many link
    > table that consists solely of the foreign keys of the relationships, then
    > Cayenne will indeed take care of things, and the relationship is
    > writable. Cayenne only sets the relationship to readonly if it's
    > flattened and *not* as described above.
    >
    > In your example, I'm assuming that Student has a pk (say, student_id),
    > Course has a pk (say, course_id), and that there is a link table
    > StudentCourseLink which has student_id and course_id in it (and only those
    > attributes).
    >
    > In this case, addToCourses should "just work". If it's not, then there's
    > a bug that needs to be worked out. If it looks like a bug, send me your
    > Data map xml files and I'll see if there's anything in those that is out
    > of place. For example, any additional attributes in StudentCourseLink
    > will be enough for Cayenne to make the relationship "read-only".
    >
    > Craig
    >
    >
    > On Fri, 22 Nov 2002, xuzhou wrote:
    >
    > > Hi all,
    > >
    > > The following italic text is excerpted from Release Notes of Cayenne 1.0b1. I think this feature is very useful, but I hava a question about it. Why the flattened relationship is readonly?
    > >
    > > Suppose the many-to-many relationship between student and course. The DataObject, Student, would have method addToCourses(Course obj). But this mothod can not be called to avoid CayenneRuntimeException is thrown. I think if this method can be called, i.e.,the flatten relationship is writable, the DataObject could be operated more convenient.
    > >
    > >
    > > 8. Added support for flattened relationships. Modeller now suggests all available
    > > paths from the source entity to the destination entity for selection. For simple flattened
    > > relationships that span a many-many link table consisting solely of fk's to the linked rows,
    > > cayenne will automatically add/remove the link records. In that case, there is no need to
    > > have an ObjEntity for the link record, and this is in fact discouraged. All other flattened
    > > relationships are set "readOnly" and cannot be modified.
    > >
    > >
    > > Regards,
    > >

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