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From Robert Zeigler <robert.zeig...@roxanemy.com>
Subject Re: Elementary Question
Date Tue, 20 Apr 2010 21:01:11 GMT
I can understand Joe's confusion: not only does cayenne generate the  
AUTO_PK_SUPPORT table, but it also inserts a row for each table,  
regardless of whether that table is using cayenne vs. db-generated ids.
I'm actually curious to know the rationale behind that one, myself. :)  
I mean, I know cayenne will fall back to using cayenne-generated ids  
if the db connected to (or corresponding driver) doesn't support auto- 
pk generation. But you should be able to detect that at schema  
generation time, and you have the mapping in hand to determine which  
entities will use db-generated pks... so... at the very least,  
shouldn't you only insert a row for those entities which need it?

The flip side, though, is that having an unused row in the db will  
have virtually no performance impact, and it keeps the generation code  
much simpler. *shrug* Just thinking out loud, I guess... I'd love to  
hear the original rationale for including all entities in the table,  
regardless of what their pk-generation strategy is. :)

Robert

On Apr 20, 2010, at 4/203:43 PM , Michael Gentry wrote:

> Hi Joe,
>
> On Tue, Apr 20, 2010 at 1:12 PM, Joe Baldwin  
> <jfbaldwin@earthlink.net> wrote:
>> Michael,
>>
>>> However, I would suggest not doing both strategies on the same  
>>> table as it will probably bite you in the long run somehow.
>>
>> That is not my intention (but I agree with you).  I am verifying  
>> all of my entities right now.  However, the Cayenne Modeler  
>> configuration was not clear.  You said that if I set the "PK  
>> Generation Strategy" to "Database Generated" but then I  
>> unintentionally had the "Create Primary Key Support" checked in the  
>> "Generate DB Schema" Options dialog, then it would create the  
>> AUTO_PK_SUPPORT table.
>>
>> It is not clear to me why you have this in two separate config  
>> parameters.  Base on your explanation (in the previous email), that  
>> if you select the "PK Generation Strategy" type for the individual  
>> entities, then the "Create Primary Key Support" option should be  
>> automatically configured at that time.
>>
>> Said a different way: why would the Cayenne Modeler create Cayenne- 
>> Managed Primary Key Support for tables with the "PK Generation  
>> Strategy" to "Database Generated"?
>
>
> I think you are confusing Cayenne Modeler's schema generation feature
> with Cayenne's runtime primary key support feature.  More below.
>
>
>> I may be wrong, but base on what you had described, it seems like  
>> Cayenne Modeler is creating a conflicting configuration in this  
>> scenario.
>
>
> There is no conflict.  Perhaps if you don't use "Database Generated"
> on any DbEntities then it would be safe in Cayenne Modeler to not have
> the checkbox when generating the SQL to create the AUTO_PK_SUPPORT
> table, but I'm not even sure I agree with that idea.  Keep in mind
> that each table can have different PK generation options (even though
> it would potentially be confusing).  Cayenne doesn't stop you from
> using the AUTO_PK_SUPPORT on some entities even when you are using
> MySQL's auto-generated PK on other entities (for example, you may need
> higher performance on some tables for bulk inserts).  Cayenne will use
> whichever strategy you specify for the entity, but allows you to
> create the AUTO_PK_SUPPORT if it is needed (your call) when you
> generate the SQL.
>
>
>>> If you have Cayenne generating the keys, it'll push them to MySQL.
>>
>> I agree, but I have clearly set "PK Generation Strategy" to  
>> "Database Generated".  So my question remains: given that the CM  
>> allows conflicting parameters, which one takes precedence here?  I  
>> have set "PK Generation Strategy" to "Database Generated", are you  
>> saying that Cayenne then ignores this configuration?
>>
>>
>>> However, I would suggest not doing both strategies on the same  
>>> table as it will probably bite you in the long run somehow.
>>
>>
>> I agree.  That is *definitely* not my intention, (But as I  
>> described above, it appears that this is very easy to do with  
>> CayenneModeler.)
>>
>> Michael, what you have described concerning CM is not intuitive.  I  
>> could easily see a designer configuring one table with Cayenne- 
>> Managed auto-generation, and another with database-auto-generation  
>> (because Cayenne Modeler allows it).  If what you are saying is  
>> true, then selecting the "Create Primary Key Support" checkbox,  
>> will override they "database-auto-generation" parameter.
>
>
> That's actually not at all what I am saying.  Selecting the "Create
> Primary Key Support" checkbox in Cayenne Modeler's schema generation
> tool just creates it in the schema.  It doesn't override what you set
> for each individual entity.  Whomever is doing the design needs to
> decide how the PKs are generated on each table.  In a lot of
> applications it is the same method for all entities, but it doesn't
> have to be that way.
>
>
>> If this is as bad as you suggest, then Cayenne Modeler should  
>> either prevent this from happening or display an explicit warning.
>
>
> I don't think it is bad at all and never suggested it was.  It is a
> very important and useful feature.
>
> mrg


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