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From Michael Shea <m...@nitido.com>
Subject Re: Talking to multiple database types with Cayenne.
Date Tue, 21 Oct 2008 15:07:41 GMT
Does getting the primary keys via the Statement.getGeneratedKeys() 
require an extra round-trip to the database? If not, I would think it 
wouldn't generate very much overhead, since I'm already sending a 
statement to the database, and receiving a response. Otherwise, yes, I 
can definitely see how it would be more efficient to batch primary keys.

Questions about Cayenne's primary key batching: Is this done globally, 
across contexts? Or would each DataContext instance manage its own batch 
of keys to use?

Thanks,


Shea.

> Interestingly, using autoincrement in mysql is probably a /hit/ in 
> performance, compared to the default strategy. Cayenne has to ask 
> mysql what the id was after every insert.
> In the default PK generation scheme, cayenne manages the ids.  Hence, 
> cayenne can batch ids and not have to talk to the db about every pk 
> for every object.
>
> Robert
>
> On Oct 21, 2008, at 10/219:12 AM , Michael Shea wrote:
>
>> Hi Andrus,
>>
>> Thanks for your reply... Of course, this is almost exactly what 
>> Cayenne is for. I erred in the question I was asking, unfortunately, 
>> so I will ask it properly this time... =). I really just have a minor 
>> question to ask:
>>
>> My two database schemas are *almost* identical, but not quite. The 
>> MySQL database creates primary keys on certain tables by using an 
>> AUTOINCREMENT column. The Oracle database creates primary keys on the 
>> equivalent tables by using a custom sequence. Is there any way for me 
>> to change the primary key generation strategy depending on which DBMS 
>> is in use? Or will I have to choose a strategy that works equally on 
>> both Oracle and on MySQL (ie, switch to using the default strategy?).
>>
>> I would ideally like to continue using the auto-increment columns on 
>> MySQL, since that intuitively seems like the most efficient method to 
>> me. I have experimented with customizing the mapping.xml file at 
>> runtime based on which type of database I'll be using, before making 
>> any calls to cayenne, that seems to work. But it's also pretty hacky, 
>> and will make maintenance more painful.
>>
>> Thanks,
>>
>>
>> Mike Shea.
>>
>>
>>> Hi Michael,
>>>
>>> Cayenne will detect the database type automatically on startup and 
>>> use the right adapter. So yes, use JNDI to abstract connection 
>>> information, beyond that no need for any extra tricks. You generic 
>>> Cayenne mapping will just work regardless of the db type.
>>>
>>> Andrus
>>>
>>>
>>>
>>> On Oct 20, 2008, at 11:42 AM, Michael Shea wrote:
>>>
>>>> Hi guys,
>>>>
>>>> I am working on a project in which I have to support multiple 
>>>> database types. They do not have to be supported simultaneously - I 
>>>> need my program to be able to run whether I am using an Oracle 
>>>> database or a MySQL database (the databases will have the same 
>>>> schema), but the database type does not change at runtime.
>>>>
>>>> I am wondering if there are any best practices or recommendations 
>>>> for how to approach this problem. Currently, I am planning on 
>>>> simply creating two sets of cayenne configuration files in 
>>>> different directories (ie, a map.xml and a cayenne.xml file), and 
>>>> just adding one or the other of these directories to the classpath, 
>>>> depending on some initial configuration parameters that tell me 
>>>> what type of database I'm accessing. The datasource is defined via 
>>>> JNDI.
>>>>
>>>> Does anyone think that this is a good idea or a bad idea, or have a 
>>>> better way of doing this? =)  I am using Cayenne 2.0.4.
>>>>
>>>> Thanks!
>>>>
>>>>
>>>> Mike Shea.
>>>>
>>>
>>
>


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