Re: Getting relation with itself(same Object)

From: Dhruti Ramani (dhrutiraman..ahoo.com)
Date: Tue Jun 21 2005 - 12:05:58 EDT

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    Thanks so much. Now its clear.
     
    Thanks again,
    Denna

    Mike Kienenberger <mkienen..laska.net> wrote:
    Dhruti Ramani wrote:
    > ya. I had that toDepPk checked in TypeToken. So I just created both
    relations from scratch so there is no "toDepPk" checked and it seems to be
    working now.
    > Thanks a lot for pointing out this.
    >
    > Does any body have any documentation to read about this "toDepPk"? I think
    this is really important issue and I saw so many questions posted here about
    it.

    Here's my understanding of it:

    If you have a master table and a dependent detail table (like EMPLOYEE and
    EMPLOYEE_ADDRESS), and you want them to be linked with the same primary key,
    then you mark the relationship from EMPLOYEE to EMPLOYEE_ADDRESS as
    "toDepPk".

    This means that EMPLOYEE can exist without EMPLOYEE_ADDRESS, but
    EMPLOYEE_ADDRESS cannot exist without EMPLOYEE.
    Furthermore, the primary key for EMPLOYEE_ADDRESS will be copied from
    EMPLOYEE. It will not be auto-pk-generated, nor will you need to set it
    manually when a new EMPLOYEE_ADDRESS is created.

    I think that toDepPk needs to be marked any time you have a primary key in
    one table that's the same as a primary key in another table. For instance,
    if you have a two-field join table where both fields are a compound key,
    then both keys are dependent primary keys. However, if you have a
    three-field join table where one field is a meaningless primary key, and the
    other two fields are foreign keys (but not primary keys), then you do NOT
    mark them as dependent primary keys.

    If you reverse-engineer your schema, the modeler seems to figure all this
    out for you.

    To make it easier to remember, there's a reverse-relationship called
    "toMasterPK" defined for DbAttributes. In some ways, I think it's
    unfortunate that toMasterPK wasn't the dominant relationship as I think most
    people think in terms of toMasterPk rather than toDepPk (I know that's what
    caused me a lot of problems -- I thought toDepPk actually meant toMasterPk).

    Hope this helps.

    -Mike

                    
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