Re: How to make a OpExpr check compatible among different versions

On Mon, Jan 13, 2020 at 4:09 PM Peter Eisentraut <
peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:

> On 2020-01-13 08:29, Andy Fan wrote:
> > During one of my works for logical rewrite, I want to check if the expr
> > is a given Expr.
> >
> > so the simplest way is:
> > if (expr->opno == 418 && nodeTag(linitial(expr->args)) == T_xxx &&
> > nodeTag(lsecond(expr->args)) == T_yyyy )
> > {
> > ..
> > }
> >
> > if we write code like above, we may have issues if the oid changed in
> > the future version.
>
> Generally, you would do this by using a preprocessor symbol. For
> example, instead of hardcoding the OID of the text type, you would use
> the symbol TEXTOID instead. Symbols like that exist for many catalog
> objects that one might reasonably need to hardcode.
>
> However, hardcoding an OID reference to an operator looks like a design
> mistake to me. Operators should normally be looked up via operator
> classes or similar structures that convey the meaning of the operator.
>

Yes, I just realized this. Thanks for your point!

> Also, instead of nodeTag() == T_xxx you should use the IsA() macro.
>
> Thank you for this as well.

> --
> Peter Eisentraut http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>