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user@domain.invalid · Guest

I have a client dataset with a parameter :
cdsOne : TClientDataSet => Param1 => paramtype = ptInput, field type ftInteger.

In the appserver, I have a TIbQuery with the same param, and a data set provider.

Back in the client, I have a method :

RequeryTheCds(aParam : Integer) ;
begin
with cdsOne do
begin
Active := False ;
Params.ParamByName('Param1').AsInteger := aParam ;
Active := True ;
end ;
end ;

If I compile this code with delphi 6 it works ok all the time.
If I compile this code with delphi 7 it only works when the parameter
passed into the function ReQueryTheCds(aParam) is different from the one
passed immediately before : ie, if I try to query twice for the same
parameter, the second time the parameter gets converted to a null.

I've followed the code in the client :
In dbclient.pas, to the method
TCustomClientDataSet.OpenCursor. this method calls
function PackageParams(...) : OleVariant ;
Inside PackageParams, when it works with the params as TParams[i],
the value is ok. Once it is assigned to the Result I lose track.
Result is a Var Array of Variant. I do not know how to look inside
it. Tried watches and evaluate/modify, but can't see how to do it.

In the server, I hooked to the before open of the query, to
check the value of the input parameter.
The first time it works ok( ie, shows 457 )
The second time I open the cds in the client( with the same parameter of 457 ),
the input parameter shows a value of 0.

Everything works ok if I keep changing the value of the parameter for the client
dataset.
One way to make it work is :

RequeryTheCds(aParam : Integer) ;
begin
with cdsOne do
begin
// Added code to make it work
if Params.ParamByName('Param1').AsInteger = aParam then
begin
Active := False ;
Params.ParamByName('Param1').AsInteger := -34546;
Active := True ;
end ;
// end of added code

Active := False ;
Params.ParamByName('Param1').AsInteger := aParam ;
Active := True ;
end ;
end ;

As you can see, it is not a solution to be happy with.

Does anybody know of the reason for this problem ?
I've tried changing midas.dll to a previous version( the one shipped with delphi 6 ),
but it still didn't work. The only way to make it work properly is compiling with
delphi 6.

TIA

user@domain.invalid · Guest

Dan Palley wrote:
<snip>

user@domain.invalid · Guest

This issue (Bug) appears to be the same as QC #8128 - the problem is this appears to be fixed in
Delphi 2005. we are using Delphi 7.

[email]user (AT) domain (DOT) inva[/email]lid wrote:

Kostas Terzides · Guest

I am sure that there is some kind of internal bug (in midas.dll
probably) that doesn't allow OleVariants that are arrays of Variants to
behave well. Your case is consistent with others posted here and from my
personal experience when I tried to use DataRequest/ OnDataRequest
having as parameter a OleVariant array of variants. I know that the
safer way to commnuicate OleVariants between a client and server
application is VarArray of VarBytes (it is said in Delphi Help), but in
case of PackageParams they must have forgotten it. Here I am going to
try to give a workaround that worked for me adjusted for your case. It
will not be trivial though and I have no easy way of testing it. Please
reply as to whether it solved your problem.Do the following:

1)Download CodeCentral number:19613

2)Add VariantStream.pas to DbClient.pas uses clause

3)Add in DBClient.pas these two procedures:

procedure VarToVarByte(var OV:OleVariant);
var
VarStream: TVariantStream;
DataOut: TMemoryStream;
P: Pointer;
S:LongString;
begin
S:= '';
VarStream := TVariantStream.Create;
DataOut := TMemoryStream.Create;
try
VarStream.WriteVariant(OV, DataOut);
SetLength(S, DataOut.Size);
P := DataOut.Memory;
Move(P^,S[1],Length(S));
finally
DataOut.Free;
VarStream.Free;
end;
OV:=StringToVariantArray(S);
end;

procedure VarFromVarByte(var OV:OleVariant);
var
VarStream: TVariantStream;
DataOut: TMemoryStream;
P: Pointer;
Flags: TVarFlags;
S:String;
begin
S:=VariantArrayToString(OV);
if Length(S) > 0 then
begin
VarStream := TVariantStream.Create;
DataOut := TMemoryStream.Create;
try
DataOut.SetSize(Length(S));
P := DataOut.Memory;
Move(S[1],P^,DataOut.Size);
OV := VarStream.ReadVariant(Flags, DataOut);
finally
DataOut.Free;
VarStream.Free;
end;
end
else
OV := Null;
end;

4)Change the following DBClient functions as follows:

function PackageParams(Params: TParams; Types: TParamTypes =
AllParamTypes): OleVariant;
var
I, Idx, Count: Integer;
begin
Result := NULL;
Count := 0;
for I := 0 to Params.Count - 1 do
if Params[I].ParamType in Types then Inc(Count);
if Count > 0 then
begin
Idx := 0;
Result := VarArrayCreate([0, Count - 1], varVariant);
for I := 0 to Params.Count - 1 do
with Params[I] do
if ParamType in Types then
begin
if VarIsCustom(Value) then
Result[Idx] := VarArrayOf([Name, VarToStr(Value),
Ord(DataType), Ord(ParamType),
Size, Precision, NumericScale])
else
Result[Idx] := VarArrayOf([Name, Value, Ord(DataType),
Ord(ParamType),
Size, Precision, NumericScale]);
Inc(Idx);
end;
VarToVarByte(result);// Added by KT
end;
end;

procedure UnpackParams(const Source: OleVariant; Dest: TParams);
var
TempParams: TParams;
HighBound, i: Integer;
begin
VarFromVarByte(Source);// Added by KT
if not VarIsNull(Source) and VarIsArray(Source) and
VarIsArray(Source[0]) then
begin
TempParams := TParams.Create;
try
for i := 0 to VarArrayHighBound(Source, 1) do
begin
HighBound := VarArrayHighBound(Source[i], 1);
with TParam(TempParams.Add) do
begin
Name := Source[i][0];
if HighBound > 1 then
DataType := TFieldType(Source[i][2]);
if HighBound > 2 then
ParamType := TParamType(Source[i][3]);
if HighBound > 3 then
Size := Source[i][4];
if HighBound > 4 then
Precision := Source[i][5];
if HighBound > 5 then
NumericScale := Source[i][6];
Value := Source[i][1]; // Value must be set last
end;
end;
Dest.Assign(TempParams);
finally
TempParams.Free;
end;
end;
end;

Kostas Terzides · Guest

If it is a bug in midas.dll try downloading 2005 version of file found
on http://www.distribucon.com. I' ve downloaded it a few days ago and
used it in my application and there doesn't seem to be any kind of
conflict. I prefer to stick to my safer approach though of converting
variants to arrays of VarByte

Dan Palley · Guest

You said the problem occurs the 2nd time you try to run the query, which is
exactly what my problem was.

user@domain.invalid · Guest

Thanks very much to everyone for their help.
The problem was solved by applying Borland's
Public beta: Delphi 7.1 Update - Database supplemental.

It brings updates to dbclient.pas, dbctrls.pas, and provider.pas, also
midas.dll, dsnap70.bpl, and vcldb70.bpl.

Once again, thanks everyone for your help.

Craig Stuntz [TeamB] · Guest

Dan Palley wrote: