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From "Mamta Satoor" <msat...@gmail.com>
Subject Re: Changes to comparable method in TypeCompiler
Date Thu, 19 Apr 2007 23:27:06 GMT
I am working on moving the comparable method from TypeCompiler to
DataTypeDescriptor. While doing that, I have found that most TypeCompiler
implementations in their comparable method do quite a bit of coding to deal
with user types. I thought Derby does not support user types anymore. To
clean the code and make it easier for me to move the existing comparable
checks into into DataTypeDescriptor, will it be ok if I don't try to
maintain code for user types and just delete it. One eg of such code can be
found in
DateTypeCompiler.comparable with following code
  /* User types know the rules for what can be compared to them */
  if (otherType.userType())
  {
   return rightType.comparable(leftType, forEquals, cf);
  }

thanks,
Mamta


On 4/19/07, Daniel John Debrunner <djd@apache.org> wrote:
>
> Mamta Satoor wrote:
>
> > I think what you are suggesting is to move comparable method out from
> > the TypeCompiler and into DataTypeDescriptor altogether. So, the
> > existing code, where we use TypeCompiler to decide if 2 types can be
> > compared or not should now call a method on DTD to determine
> > comparability. This might be cleaner than stuffing collation information
> > in CharTypeCompiler but I am just wondering why was comparable not
> > defined on DTD at the very start. Why do we go through TypeCompiler and
> > what functionality does TypeCompiler provide that DTD does not? In other
> > words, I don't understand the connection between TypeCompiler and DTD
> > and how they fit together.
>
> It's not that TypeCompiler provides functionality that DTD does not, but
> instead DTD has functionality/information that TypeCompiler does not.
> Ignoring the "compiler" aspect for the moment there are two components
> to a DataTypeDescriptor, the underlying SQL type (INTEGER, CHAR,
> VARCHAR, XML etc.) represented as TypeId and attributes of the
> descriptor (nullablity, length, precision, scale and now collation).
>
> Thus
>
> DTD = TypeId + {attributes}
>
> Some functionality is applicable to a type regardless of a specific
> DTD's attributes, thus methods for that functionality can be declared on
> TypeId instead of DTD.
>
> Some functionality on the other hand needs the attribute information as
> well, say the display length of a type is a function of its
> length/precision&scale and its underlying SQL type.
>
> The collation changes have moved the comparable check from being only
> reliant on the SQL type (TypeId) to being dependent on the type's
> attributes (collation type and implicit/explicit). Thus the original
> location for the comparable method made sense, but now does not.
>
> The TypeCompiler/TypeId split was due to an early plan to have a
> execute-only version of the technology, this never happened as there was
> no demand for it. One of the benefits of a SQL engine is the ability to
> execute arbitrary queries, which would not be available in an execute
> only version. Code cleanup could be done here which probably would
> decrease the footrprint of derby.
>
> HTH,
> Dan.
>
>
>

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