TClientDataSet read Binary field to TStream - sql-server

Question

i have tried this every way that I possible can, but cannot seem to resolve this. I am working with DBExress in Delphi XE3 writing a REST DataSnap Server.
I have data stored in MSQL in a Binary(384) field and Binary is as far as I know that same as a BLOB/Image field as it is all Binary data.
When trying to stream this data to a TStream I receive an exception error and have tried the following
var
STemplate : TStream;
begin
......
Template := TBlobField.Create(cdsBSUserTemplates.FieldByName('bTemplate'));
TBlobField(cdsBSUserTemplates.FieldByName('bTemplate')).SaveToStream(STemplate); //exception
......
end;
and I have tried
var
STemplate : TStream;
begin
......
Template := TBlobField.Create(cdsBSUserTemplates.FieldByName('bTemplate'));
STemplate := cdsBSUserTemplates.CreateBlobStream(Template, bmRead); //exception
......
end;
I can return the value .AsString, but it is Bytes and then I need to try and fix what I have read from that field.
Any idea what else I can try?

Answer 1

You're working much too hard. :-)
You need to properly create the stream, and then just let the field write to it.
var
Output: TMemoryStream;
Fld: TBlobField;
begin
// Use of variable makes it more readable
Fld := cdsBSUserTemplates.FieldByName('bTemplate') as TBlobField;
Output := TMemoryStream.Create;
try
Fld.SaveToStream(Output);
Output.Position := 0;
// Do whatever with the output stream
finally
Output.Free;
end;
end;
After your comment that you might not be using a TBlobField (which would have been nice to know before I posted my answer), you can try this instead (untested, because I clearly don't have your data):
var
Output: TMemoryStream;
Fld: TField;
Bytes: TArray<Byte>;
begin
Fld := ADOQuery1.FieldByName('bTemplate');
Output := TMemoryStream.Create;
try
if Fld.IsBlob then
TBlobField(Fld).SaveToStream(Output)
else
begin
Fld.GetData(Bytes);
Output.WriteData(Bytes, Length(Bytes));
end;
// Do whatever with output
finally
Output.Free;
end;
end;