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From Michael Gentry <mgen...@masslight.net>
Subject Re: Primary Keys
Date Fri, 02 Nov 2012 23:02:07 GMT
Hi Garth,

If you have a legacy schema with meaningful PKs, it is fine to map
them.  In general, especially when creating a new schema, meaningful
PKs are to be discouraged, but sometimes you don't have a choice.

mrg


On Fri, Nov 2, 2012 at 3:51 PM, Garth Keesler <garthk@gdcjk.com> wrote:
> This issue remains a hot-button topic out there so here's my situation: I
> have a list of abbreviated Vendor Names that haven't changed in ten years
> altho it has been added to. That name is meaningful and is used in a variety
> of places as a foreign key. It would also make a very nice PK since it is
> permanent and guaranteed unique. One other advantage is that it is
> meaningful wherever it is used so joins are frequently avoided. I've read
> many Pro vs Con on meaningful PKs and FKs and one worry is how to recover
> from a software error that jumbles these values. How to best reconnect? One
> approach might be to unnormalize and copy the short name while still using a
> meaningless FK but that is disaster waiting to happen.
>
> I'm wide open to suggestion on this.
>
> Thanx,
> Garth
>
>
> On 11/01/2012 05:44 PM, Aristedes Maniatis wrote:
>>
>> On 2/11/12 6:35am, Garth Keesler wrote:
>>>
>>> Can the PK as specified in the DBEntity be different than the PK actually
>>> specified in the schema? I ask because I use DB-generated integer sequences
>>> as the primary keys which are never used in the software. The software uses
>>> an abbreviated form of the vendor name that is forced to be unique within
>>> the table. Would it make more sense to specify that the shortened name is
>>> the "real" PK in the definition of the DBEntity (which is hand-created, not
>>> extracted from the schema)? FYI, this column is also used in may foreign
>>> keys. Speaking of FKs, if I specify a relation in the DBEntity, should it
>>> share the name of the FK specified in the schema or are they unrelated?
>>
>>
>> I suggest that you map Cayenne's concept of the PK to the real PK since
>> that is what you'll want to use for FK joins from other tables. Then just
>> create a normal field for your vendor code and add validation to keep it
>> unique. Making the vendor code the PK in any way is likely to cause lots of
>> pain down the track when one of your vendors changes names and wants a new
>> code.
>>
>> One of the reasons Cayenne hides the PK from the Java entities by default
>> is that it is almost never a good idea to expose the PK to users of the
>> software.
>>
>>
>> Ari
>>
>>
>

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