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ZeosLib can't correctly compare Extended value when creating update query
Posted: 20.03.2020, 14:25
by DPStano
CompareExtended_Equals from ZDbcCache will return an incorrect result for the "same" numbers
Re: ZeosLib can't correctly compare Extended value when creating update query
Posted: 23.03.2020, 14:51
by marsupilami
Could you post some example code please?
Best regards, Jan
Re: ZeosLib can't correctly compare Extended value when creating update query
Posted: 25.03.2020, 17:43
by DPStano
it's definitely regression, you can't compare two floats this way,
https://floating-point-gui.de/errors/comparison/
just load some decimal number to the dataset, update dataset without changes (Edit and Post) and zeos will create update query that contains your decimal field even field not changed.
I'm hooking that code for now (it's not a universal solution, epsilon it's set for our needs)
Code: Select all
function InterceptCompareExtended_Equals(const Null1, Null2: Boolean; const V1, V2): Integer;
begin
if Null1 and Null2 then
Result := 0
else
Result := CompareValue(PExtended(V1)^, PExtended(V2)^, 0.000001);
end;
var
TrampolineGetCompareFunc: function(const Self: TZRowAccessor; ColumnIndex: Integer; const CompareKind: TComparisonKind): TCompareFunc = nil;
function InterceptGetCompareFunc(const Self: TZRowAccessor; ColumnIndex: Integer; const CompareKind: TComparisonKind): TCompareFunc;
begin
if (Self.GetColumnType(ColumnIndex) = stBigDecimal) and (CompareKind = ckEquals) then
Result := InterceptCompareExtended_Equals
else
Result := TrampolineGetCompareFunc(Self, ColumnIndex, CompareKind);
end;
@TrampolineGetCompareFunc := InterceptCreate(@TZRowAccessor.GetCompareFunc, @InterceptGetCompareFunc);
Re: ZeosLib can't correctly compare Extended value when creating update query
Posted: 26.03.2020, 09:29
by marsupilami
Hello
DPStano wrote: ↑25.03.2020, 17:43
it's not a universal solution, epsilon it's set for our needs
This is the main problem - we cannot know a correct epsilon to use. We only could try to generate an epsilon if the database field is a DECIMAL or NUMERIC field.
But then - the current value of a TFlotField or TExtendedField should be determined when we load the data. The question for me is - why should it change if one does a edit / post cycle without touching it? Maybe this has to do with the conversion between a binary representation and a decimal representation. In that case epsilon could be very very small - compared to the values in the float...
Zeos 7.3 supports NUMERIC and DECIMAL fields correctly now by using TBCDField and TFMTBCDField. Maybe this solves your problem?
Best regards,
Jan
Re: ZeosLib can't correctly compare Extended value when creating update query
Posted: 26.03.2020, 17:40
by DPStano
thx for info, will switch to TBCDFields in future