TPARAMS和OLEVARIANT相互转换

所谓的“真3层”有时候是需要客户端上传数据集的TPARAMS到中间件的。

现在，高版本的DATASNAP的远程方法其实也是直接可以传输TPARAMS类型的变量，但是DELPHI7（七爷）、六爷它们是不支持的。

高版本的DATASNAP要让六爷、七爷它们调用，不能直接传TPARAMS，得转换。

procedure VariantToParams(input: OleVariant; par: TParams);
var
  n, i: integer;
begin
  try
    n := 0;
    i := 0;
    par.Clear;
    while VarArrayHighBound(input, 1) >= (n + 5) do
    begin
      par.CreateParam(TFieldType(input[n + 1]), input[n + 2], TParamType(input[n + 4]));
      par.Items[i].Value := input[n + 3];
      par.Items[i].Size := input[n + 5];
      n := n + 5;
      i := i + 1;
    end;
  except
    Exit;
  end;
end;

function ParamsToVariant(par: TParams): OleVariant;
var
  n, i: integer;
begin
  try
    Result := VarArrayCreate([1, par.Count * 5], VarVariant);
    n := 0;
    i := 0;
    while par.Count > i do
    begin
      Result[n + 1] := Ord(par.Items[i].DataType);
      Result[n + 2] := par.Items[i].Name;
      Result[n + 3] := par.Items[i].Value;
      Result[n + 4] := ord(par.Items[i].ParamType);
      Result[n + 5] := par.Items[i].Size;
      i := i + 1;
      n := n + 4;
    end;
    result := Result;
  except
    Exit;
  end;
end;

其实，PARAMS和OLEVARIANT相互转换的函数，DELPHI已经现成提供了：

DBCLITNT.PAS

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;
end;
end;

procedure UnpackParams(const Source: OleVariant; Dest: TParams);
var
TempParams: TParams;
HighBound, i: Integer;
begin
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;