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Date: Tue, 03 Jan 2006 11:02:05 +0100
From: Michael Bouschen <mbo.tech@spree.de>
Organization: Tech@Spree Engineering
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To: jdo-dev@db.apache.org, JDO Expert Group <jdo-experts-ext@Sun.COM>
Subject: Re: [VOTE] Issue 139: Add attribute field-type to element field
References: <A59EAD3E-6F44-47EA-9970-EDBEC99ED533@Sun.COM>
 <200512210811.06546.andy@jpox.org>
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Hi Craig,

+1

Regards Michael

> Another vote on this proposal. I've added the ability to specify 
> multiple comma-delimited types to element-type, key-type, value-type, 
> and field-type but specified that this is not portable.
> 
> 
> Issue 139:
> 
> This would allow more specific field type to be specified at deployment 
> time compared to compile time. For example, a field of type Object could 
> be specified in the jdo metadata as containing only instances of type 
> SimpleClass.
> 
> <proposal>
> 18.14 ELEMENT field
> <!ATTLIST field field-type CDATA #IMPLIED>
> The field-type attribute is used to specify a more restrictive type than 
> the field definition in the class. This might be required in order to 
> map the field to the datastore. To be portable, specify the name of a 
> single type that is itself able to be mapped to the datastore (e.g. a 
> field of type Object can specify field-type=�Integer�). To specify 
> multiple types that the field might contain, use a comma-separated list 
> of types, although this cannot be portably mapped.
> 18.14.1ELEMENT collection
> element-type
> The element-type attribute specifies the type of the elements. The type 
> name uses Java language rules for naming: if no package is included in 
> the name, the package name is assumed to be the same package as the 
> persistence-capable class. Inner classes are identified by the "$" 
> marker. Classes Boolean, Byte, Character, Double, Float, Integer, Long, 
> Number, Object, Short, String, and StringBuffer are treated exactly as 
> in the Java language: they are first checked to see if they are in the 
> package in which they are used, and if not, assumed to be in the 
> java.lang package. To be portable, specify the name of a single type 
> that is itself able to be mapped to the datastore (e.g. a field of type 
> Object can specify field-type=�Integer�). To specify multiple types that 
> the field might contain, use a comma-separated list of types, although 
> this cannot be portably mapped.
> 18.14.2 ELEMENT map
> The key-type and value-type attributes specify the types of the key and 
> value, respectively. They follow the same rules as element-type in 
> element collection.
> 18.14.3 ELEMENT array
> The element-type attribute is used to specify a more restrictive type 
> than the field definition in the class. This might be required in order 
> to map the field to the datastore. It follows the same rules as 
> element-type in element collection.
> </proposal>
> 
> Craig
> 
> On Dec 28, 2005, at 1:33 PM, Michael Bouschen wrote:
> 
>> Hi Craig,
>>
>>> Hi Andy,
>>>
>>> I don't have a problem with using the element-type to be a 
>>> comma-separated list as a vendor extension, but in general there is 
>>> no way to map a heterogeneous (Object or interface type) field.
>>
>>
>> does this apply the metadata attributes field-type, element-type, 
>> key-type and value-type?
>>
>>>
>>> So I don't think that we should specify the comma-separated list of 
>>> possible types as a standard technique.
>>>
>>> What do others think about this?
>>
>>
>> I think support for a field with multiple types in its field-type 
>> attribute should not be required. But maybe it makes sense to specify 
>> the syntax as a comma separated list of type names in case a JDO 
>> implementation does support this feature.
>>
>> Regards Michael
>>
>>>
>>> Craig
>>>
>>> On Dec 21, 2005, at 12:11 AM, Andy Jefferson wrote:
>>>
>>>> Hi Craig,
>>>>
>>>>> This proposal would allow more specific field type to be specified at
>>>>> deployment time compared to compile time. For example, a field of
>>>>> type Object could be specified in the jdo metadata as containing only
>>>>> instances of type SimpleClass.
>>>>
>>>>
>>>>
>>>> I don't read the proposal as saying that the user should specify the 
>>>> type(s) as comma-separated if they want a field declared as Object 
>>>> to store class A or class B or class C. What does the user do when 
>>>> they have a field declared as Object and want to do this ?
>>>>
>>>>
>>>> -- 
>>>> Andy
>>>
>>>
>>>
>>> Craig Russell
>>>
>>> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
>>>
>>> 408 276-5638 mailto:Craig.Russell@sun.com
>>>
>>> P.S. A good JDO? O, Gasp!
>>>
>>>
>>
>>
>> -- 
>> Michael Bouschen Tech@Spree Engineering GmbH
>> mailto:mbo.tech@spree.de http://www.tech.spree.de/
>> Tel.:++49/30/235 520-33 Buelowstr. 66
>> Fax.:++49/30/2175 2012 D-10783 Berlin
>>
> 
> Craig Russell
> 
> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
> 
> 408 276-5638 mailto:Craig.Russell@sun.com
> 
> P.S. A good JDO? O, Gasp!
> 
> 


-- 
Michael Bouschen		Tech@Spree Engineering GmbH
mailto:mbo.tech@spree.de	http://www.tech.spree.de/
Tel.:++49/30/235 520-33		Buelowstr. 66			
Fax.:++49/30/2175 2012		D-10783 Berlin