I agree with you, on that. With current specification, if I am not wrong,
there is no way to achieve what you have suggested in a portable way.
There has to be generic collection (name value pair) class supplied by the EJB
specification which should be returned as a result of retrieving
multiple attributes, or some other alternatives.
Dominic Savio
www.objectfrontier.com
On Fri, 3 Aug 2001 17:17:21 +0100, Ian McCallion <[EMAIL PROTECTED]> wrote:
>Dominic Savio wrote:
>>
>> I suppose you have mapped the Imagedata field to BLOB database type.
>> If I understand correctly, even if the container retrieves all attributes
>> of the bean (result of ejb-ql), the Imagedata field will be just a handle
>> to the stream object. Unless we invoke any method on that, i think the
>> handle will not retrive the actual data from the data source.
>
>> On Fri, 3 Aug 2001 12:14:34 +0100, Ian McCallion <[EMAIL PROTECTED]>
>wrote:
>>
>> >Suppose I have an entity called Image with four CMP fields:
>> >
>> >- Primary Key
>> >- Description (100 bytes)
>> >- Date (8 bytes)
>> >- Imagedata (1 meg)
>> >
>> >I'd like to implement an ejbSelectByDate(Date) method that selects (PK,
>> >Description) and use this method in a ejbHomeGetDescriptionsOn(Date) method
>> >that simply returns the data to the client so that I can display the
>> >descriptions to the user who can then select images to view based on the
>> >descriptions.
>> >
>> >As far as I can see, this is straightforward with SQL, but impossible with EJB
>> >QL. Have I missed something?
>
>Dominic, that's a good point for the particular case of mapping a large field to
>a BLOB. It is not getting to the heart of the problem though, as I'll still have
>to instantiate each Entity Bean, involving a minimum of n+1 SQL calls to get
>what I can get in a single SQL call. According to the spec:
>
> SELECT l.product FROM Order AS o, IN(o.lineItems) l
>
>returns a list of products specified in a particular Order. On this basis:
>
> SELECT l.quantity FROM Order AS o, IN(o.lineItems) l
>
>would presumably return a list of quantities of the products ordered. But there
>is no way of correlating the two lists, and no way of getting a combined list.
>What we'd like to be able to do is have:
>
> SELECT (l.product, l.quantity) FROM Order AS o, IN(o.lineItems) l
>
>return a simple serializable collection of value objects containing product and
>quantity. Perhaps this is one complication too far for the spec writers at this
>stage, but it seems to limit the usefulness of EJB QL quite severely.
>
>========================================
>Ian McCallion
>Alexis Systems Limited
>Romsey, UK
>Tel: +44 1794 514883
>Fax: +44 1794 501692
>========================================
>
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