What's the best way to store a Delphi set in a dataset?

Question

The title pretty much says it all. I'm using a TClientDataset to store an array of objects, and one of the objects has a member defined as a set of an enumerated type. As I understand it, Delphi sets are bitfields whose size can vary from 1 to 32 bytes depending on how much data they contain, and Delphi doesn't define a TSetField. What sort of field should I use to load this value into?

See also [How to save/load Set of Types?](http://stackoverflow.com/q/9553510/757830). — NGLN, Dec 25 '15 at 20:27

score 14 · Accepted Answer · answered Dec 07 '08 at 14:02

You could use a TBytesField or a TBlobField

ClientDataSet1MySet: TBytesField, Size=32

var
  MySet: set of Byte;
  Bytes: array of Byte;
begin
  MySet := [1, 2, 4, 8, 16];

  // Write
  Assert(ClientDataSet1MySet.DataSize >= SizeOf(MySet), 'Data field is too small');

  SetLength(Bytes, ClientDataSet1MySet.DataSize);
  Move(MySet, Bytes[0], SizeOf(MySet));
  ClientDataSet1.Edit;
  ClientDataSet1MySet.SetData(@Bytes[0]);
  ClientDataSet1.Post;

  // Read
  SetLength(Bytes, ClientDataSet1MySet.DataSize);
  if ClientDataSet1MySet.GetData(@Bytes[0]) then
    Move(Bytes[0], MySet, SizeOf(MySet))
  else
    MySet := []; // NULL
end;

1) To make your sample even clearer I propose to change the "ClientDataSet1MySet.SetData(@Bytes[0])" into "ClientDataSet1MySet.AsBytes := Bytes" 2) In the // Read block (on the Move line), I think that you must change the "SizeOf(MySet)" to "ClientDataSet1MySet.DataSize" to be consistent. — Roeland Van Heddegem, Dec 04 '13 at 16:55

Fabricio Araujo · Answer 2 · 2008-12-08T21:23:09.130

You can convert them to Byte, like this:

var
  States : TUpdateStatusSet; // Can be any set, I took this one from DB.pas unit
  SetAsAInteger: Integer;
  dbs: Pointer; // Here's the trick
begin
  States := [usModified, usInserted]; // Putting some content in that set
  dbs := @States;
  SetAsAInteger := PByte(dbs)^;
  //Once you got it, SetAsAInteger is just another ordinary integer variable.
  //Use it the way you like.
end;

To recover from anywhere:

var
  MSG: string;
  Inserted, Modified: string;
  States: TUpdateStatusSet;
  MySet: Byte;

begin
  while not ClientDataSet.Eof do
  begin
    //That's the part that interest us
    //Convert that integer you stored in the database or whatever 
    //place to a Byte and, in the sequence, to your set type.
    iSet := Byte(ClientDatasetMyIntegerField);// Sets are one byte, so they
                                              //  fit on a byte variable  
    States := TUpdateStatusSet(iSet);
    //Conversion finished, below is just interface stuff


    if usInserted in States then
      Inserted := 'Yes';
    if usModified in States then
      Modified := 'Yes';
    MSG := Format('Register Num: %d. Inserted: %s. Modified:%s',
                  [ClientDataSet.RecNo, Inserted, Alterted]);
    ShowMessage( MSG );
    ClientDataset.Next;
  end;

end;

That works just fine until you need more than 32 bits. Sets go up to 256 bits, and I'm in a situation where I might need a good fraction of that space. — Mason Wheeler, Dec 09 '08 at 19:06

score 0 · Answer 3 · answered Dec 05 '13 at 08:39

Based on the example of Andreas, but made somewhat simpler and clearer IMHO.

Tested on XE2

You could use a TBytesField or a TBlobField

ClientDataSet1MySet: TBytesField, Size=32

1) Writing

var
  MySet: set of Byte;
  Bytes: TBytes;
begin
  MySet := [0];

  // Write
  Assert(ClientDataSet1Test.DataSize >= SizeOf(MySet), 'Data field is too small');

  SetLength(Bytes, ClientDataSet1Test.DataSize);
  Move(MySet, Bytes[0], SizeOf(MySet));
  ClientDataSet1.Edit;
  ClientDataSet1Test.AsBytes := Bytes;
  ClientDataSet1.Post;
end;

2) Reading

var
  MyResultSet: set of Byte;
begin
  Move(ClientDataSet1Test.AsBytes[0], MyResultSet, ClientDataSet1Test.DataSize);
end;

What's the best way to store a Delphi set in a dataset?

3 Answers3

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