Kent wrote:
> Along the same lines, is there something we can do about nvl()
> (oracle) versus coalesce() (ansi)?
>
> They aren't exactly the same, unfortunately (nvl takes exactly 2
> arguments, no more), so maybe there is nothing 'official' you can do,
> but can you help me work it out for my project?
>
> I assume it is very similar to what you helped me out with
> above...something like this:
>
> ============================================================
> from sqlalchemy.sql.expression import ColumnElement
> from sqlalchemy.ext.compiler import compiles
> from sqlalchemy.types import DateTime, Date
>
> class current_date(ColumnElement):
> type = Date()
>
> @compiles(current_date)
> def _compiler_dispatch(element, compiler, **kw):
> if compiler.dialect.name == 'oracle':
> if compiler.dialect.use_ansi:
> return "trunc(current_date)"
> else:
> return "trunc(sysdate)"
> else:
> # assume postgres
> return "current_date"
> ============================================================
>
>
> But the main difference is it takes arguments.
>
> Is there a clever way to return the appropriate function, something
> like this:
>
> def ....
> if compiler.dialect.name == 'oracle':
> return func.nvl
> else:
> # assume postgres
> return func.coalesce
I will add this to the docs:
from sqlalchemy import *
from sqlalchemy.ext.compiler import compiles
from sqlalchemy.sql.expression import FunctionElement
class coalesce(FunctionElement):
name = 'coalesce'
@compiles(coalesce)
def compile(element, compiler, **kw):
return "coalesce(%s)" % compiler.process(element.clauses)
@compiles(coalesce, 'oracle')
def compile(element, compiler, **kw):
if len(element.clauses) > 2:
raise TypeError("coalesce only supports two arguments on Oracle")
return "nvl(%s)" % compiler.process(element.clauses)
print coalesce(5, 6)
from sqlalchemy.dialects import oracle
print coalesce(5, 6).compile(dialect=oracle.dialect())
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