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From Daniel John Debrunner <...@apache.org>
Subject Re: how should store get an object based on format id and collation id?
Date Mon, 16 Apr 2007 22:12:40 GMT
Mike Matrigali wrote:
> 
> 
> Daniel John Debrunner wrote:
>> Mamta Satoor wrote:
>>
>>> I spent some time on points 1(using Monitor to get dvd directly) and 
>>> 3(optimized allocation, caching some of the work.) which requires us 
>>> to solve the problem of how to get the InstanceGetter to return the 
>>> correct DVD for character types. Let me first briefly describe how 
>>> the InstanceGetter works for DVDs currently.
>>
>>
>> I'm a little unclear on exactly the problem this is trying to solve. I 
>> got a little lost in the details, but does it take account of the fact 
>> that the registered format ids are system wide and there can be 
>> databases with different default collations in the same system?
>>
>> Also the use of InstanceGetters seem to complicate this issue, once 
>> one knows one has a collation type and one is using the 
>> DataValueFactory then one can have methods on DVF that return 
>> DataValueDescriptors directly, no need to go through the indirection 
>> of InstanceGetters. They are a mechanism used when the type of the 
>> object is not known, here the type is known as a DVD.
>>
>> One of the points to note is that the correct DVD type for collation 
>> is only needed when collation is actually occurring. If a collator 
>> based column is read in using SQLChar then it's not a problem as long 
>> as a switch to the collator version occurs during comparisons. Earlier 
>> I has suggested methods to perform this switch on StringDataType, 
>> something like getCollationValue(int collationType).
> I am stuck on this.  Is your proposal to carry around a collation type
> field in the SQLChar class and delay the underlying association with
> a class that does collation until the first method called that requires
> collation?  I thought you specifically did not want a collation type
> to be available from a dvd.  I am sure I am missing something in your
> proposal.

I'd assumed that every time a collation was needed that enough meta data 
was available to determine the collation. For example with language 
based comparisons the collation will be known at compile time and thus 
can be used. For index based collation the metadata must be available 
already today because the collations must be using the asc/desc flag.

Assuming that is true, then no need to store the collation in the 
DVD/SQLChar.

Dan.


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