On Wed, 22 Apr 2009, Adam Lubszczyk wrote:
Hi,
> Thera are BASE.DBF and BASE.NTX with key "FunctionX(Field1)" or key:
> Field1+VariableX
> Make same program with line:
> USE base INDEX base
> In Clipper it is OK, I open base with index.
Because during open Clipper does not check if index expressions are valid.
The RTE will appear later when it will have to evaluate some expressions.
> In Harbour I get error "Undefined function FUNCTIONX" or "Variable does not
> exist: VARIABLEX"
> WHY ?
Because Harbour checks if all index expressions (KEY/FOR) are valid when
index is open. It helps to detect problem immediately. IMHO it's much
better then later pseudo random RTE like in Clipper.
> I need FunctionX() or VariableX _only_ if I modify or append record.
Not true. It's necessary to navigate the index. Though in some cases
depending on SHARED/EXCLUSIVE mode and used caches it may be not necessary
for some time.
I guess you created general theory from some situation which happened with
your code but it's not true.
> Maybe I wont only skip by order or seek in base.
> If key is sample "Func1(Field1)+Func2(Field2)+VariableX",
> I can seek by: DBSEEK( MyFuncEmulateKeyValue() ), I not need Func1(),
> Func2() and VariableX
Try this code with Clipper:
/*** t01 ***/
proc main()
field F
dbcreate("_tst",{{"F","C",1,0}})
use _tst
dbappend(); dbappend(); dbappend()
index on MYFUNC(F) to _tst
close
return
func myfunc( f )
return f
to create table and index and this code:
/*** t02 ***/
proc main()
use _tst index _tst
dbgoto(2)
while !eof()
? recno()
dbskip()
enddo
return
Please note that when you replace
dbgoto(2)
with:
dbgoto(1)
it will work without RTE but only in EXCLUSIVE mode. It happens because
record 1 is still active and in exclusive mode is not discarded bu GOTO
operation. In SHARED mode it will always generate RTE.
best regards,
Przemek
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