Thanks a lot Hemant, I get to understand why. Glad to know that pramati server
supports this scenario.
Chandra
On Thu, 31 Jan 2002 11:24:52 +0530, Hemant Khandelwal <[EMAIL PROTECTED]> wrote:
>The identity of an entity is established by the container when the call to
>ejbCreate is over. This includes associating the primary key value with the
>entity.
>
>Now suppose that setting cmr-value in the ejbCreate method is allowed. The
>container then, cannot enforce setting the primary key cmp-field value
>before setting a cmr-field. With the presence of database constraints like
>primary key-foreign key, while creating/updating the record for the child
>table, primary key value of the parent table is required.
>
>For example, consider one-to-one relationship between CustomerBean and
>AddressBean and the corresponding table.
>
>CustomerTable
>----------------
>customerId (primary key)
>name
>
>AddressTable
>-----------------
>addressId
>zip
>customerId (foreign key)
>
>Without the restriction of setting cmr-field in the ejbPostCreate, ejbCreate
>of CustomerBean can be written like:
>
>CustomerBean:
> ejbCreate(...){
> AddressLocal address = createAddress(...);
> setAddress(address);
> //Setting pk after setting cmr-field
> setCustomerId("cust-101");
> ...
> }
>
>In this case, a container is forced to defer setting the value of
>AddressTable.customerId in the database after the record is created in the
>CustomerTable. Moreover, the problem is compouneded by the fact that
>container cannot differentiate the ejbCreate written in this manner with the
>following ejbCreate.
>
>CustomerBean:
> ejbCreate(...){
> //Setting pk before setting any cmr-field
> setCustomerId("cust-101");
> AddressLocal address = createAddress(...);
> setAddress(address);
> ...
> }
>
>In either way, container has to do deferred insertion/update.
>
>However, when the relationships are set in the ejbPostCreate, container may
>or may not defer the inserts based upon the strategy it uses.
>
><vendor>
>Pramati Application Server identifies the type of constraint existing
>between the two related tables, so that the database insertion and cmr-field
>value can be set while honouring the database constarints specified by the
>user.
></vendor>
>
>Regards,
>Hemant
>Server Team,
>www.pramati.com
>
>----- Original Message -----
>From: "Evan Ireland" <[EMAIL PROTECTED]>
>To: <[EMAIL PROTECTED]>
>Sent: Thursday, January 31, 2002 6:14 AM
>Subject: Re: use of ejbPostCreate()
>
>
>Chandra kumar wrote:
>
>> ...
>
> >
>
>> Back to my question again, Let's say we set the relationship value in
>ejbPostCreate() as specified in the spec. What if the
>relationship(forignkey) field is set as not null in child table and DB
>insert happening after ejbCreate(), insert will fail. I think I'm missing
>something here, because I still don't seem to understand significance of the
>statement in the spec that says "do not set the cmr-fields in ejbCreate()"
>
>
>Two issues here:
>
>(1) The spec is taking a 'logical' view that before ejbCreate returns, the
> entity does not exist so you cannot enter it into relationships at that
> time.
>
>(2) Having foreign key references that are defined as "not null" will
> generally be prone to causing constraint violations in some
> situations. Whether inserts are deferred (or for that matter, ordered)
> in such a way as to prevent foreign key constraint violations is not
> covered by the spec, but it is a quality of implementation issue.
>
> The spec does not guarantee that any EJB 2.0 CMP implementation will
> be able to work with arbitrary database-level constraints that you
> might have defined. The spec doesn't even require support for foreign
> keys at all!
>
>
>> I humbly seek help on this to understand better.
>>
>> Thanks,
>> Chandra
>>
>> On Thu, 31 Jan 2002 10:09:51 +1300, Evan Ireland <[EMAIL PROTECTED]>
>wrote:
>>
>>
>>>Chandra kumar wrote:
>>>
>>>
>>>>Section 10.5.2 of EJB 2.0 spec states the following:-
>>>>
>>>>"....... The entity Bean Provider must not attempt to modify the values
>of cmr-fields in an ejbCreate<METHOD(...) method; this should be done in the
>ejbPostCreate<METHOD(...) method instead. ......"
>>>>
>>>>I've tried my best to understand the above. But I could not succeed.
>>>>Here are my questions (note: when we have strict DB constraints in
>place):
>>>>
>>>>1. How the above statement holds good, if we want set the relationship
>value in child's ejbPostCreate(), If DB insert is issued after ejbCreate().
>>>>
>>>
>>>That's up to the CMP implementation. Sybase EAServer (by default) will do
>>>an 'insert' after ejbCreate and will do an 'update' after ejbPostCreate
>>>(of course if no fields have changed, the 'update' can be skipped).
>>>
>>>
>>>
>>>>2. Let's say if DB insert is deferred to end of ejbPostCreate(), then we
>cannot create child object(s) in ejbPostCreate() of Parent.
>>>>
>>>
>>>That depends on whether your database schema has foreign key constraints
>that
>>>will break if the insert is deferred.
>>>
>>>
>>>
>>>>If this is something very obvious, it'd probably irritate some to see a
>long mail with examples. So I defer that to you.
>>>>
>>>>Any help would be greatly appreciated.
>>>>
>>>>Thanks for time and consideration,
>>>>Chandra
>>>>
>>>>=========================================================================
>==
>>>>To unsubscribe, send email to [EMAIL PROTECTED] and include in the
>body
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>>>>[EMAIL PROTECTED] and include in the body of the message "help".
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>--
>>>__________________________________________________________________________
>_____
>>>
>>>Evan Ireland Sybase EAServer Engineering
>[EMAIL PROTECTED]
>>> Wellington, New Zealand +64 4
>934-5856
>>>
>>>==========================================================================
>>>To unsubscribe, send email to [EMAIL PROTECTED] and include in the
>body
>>>of the message "signoff EJB-INTEREST". For general help, send email to
>>>[EMAIL PROTECTED] and include in the body of the message "help".
>>>
>>>
>>
>>
>
>
>--
>____________________________________________________________________________
>___
>
>Evan Ireland Sybase EAServer Engineering
>[EMAIL PROTECTED]
> Wellington, New Zealand +64 4
>934-5856
>
> ==========================================================================
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