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Date: Mon, 11 Jun 2007 19:55:51 -0700
From: Daniel John Debrunner <djd@apache.org>
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Subject: Re: Setting correct collation on return type of a user defined
 function
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Mamta Satoor wrote:

> The schema information is available at CreateAliasNode.bindStatement 
> time. I was thinking of modifying the collation type of return type 
> (returnType variable in) of RoutineAliasInfo inside 
> CreateAliadNode.bindStatement but there is not a way to do that 
> currently because RoutineAliasInfo does not have a method to change the 
> TypeDescriptor of it's return type. I can fix that easily by adding a 
> new method to RoutineAliasInfo like following
>  
>  public void setReturnType(TypeDescriptor typeWithCorrectCollation) {
>   returnType = typeWithCorrectCollation;
>  }

RoutineAliasInfo doesn't have any set methods as it is intended to be an 
immutable (at least logically). This allows instances of it to be passed 
around without worrying about other users changing its definition. 
Immutable objects can benefit code quality by not leading to bugs where 
state changes in one part of the code cause unexpected changes elsewhere.

> But the other problem is that there is no way to change a TypeDescriptor 
> object. All I want to do is something like following in 
> CreateAliasNode.bindStatement
> 
>   if (aliasType == AliasInfo.ALIAS_TYPE_FUNCTION_AS_CHAR) {
>    RoutineAliasInfo rai = (RoutineAliasInfo)aliasInfo;
>    TypeDescriptor returnType = rai.getReturnType();
>    //pseudo code. Get the schema descriptor sd for function's schema
>    returnType.setCollationType(sd.getCollationType());
>    rai.setReturnType(returnType);
>    }
> 
> But since there is no way to change the collation type on the 
> TypeDescriptor interface, do I just somehow CAST returnType to 
> TypeDescriptorImpl and change the collation type on it. This (CASTing) 
> doesn't seem right to me but before I spend too much time on the 
> problem, I wanted to see if anyone had any ideas/feedback.

TypeDescriptor is also logically immutable for similar reasons, one 
doesn't want the type of a column in a catalog to be changed by some 
code re-using the descriptor and changing its nullability (or 
collation). I'm cleaning up the TypeDescriptor under DERBY-2775.

Dan.