begin
  if FieldDefs.Count = 0 then begin
    for I := 0 to FieldCount - 1 do begin
      with Fields[I] do
        if (FieldKind in fkStoredFields) and not (DataType in ftSupported) then
          ErrorFmt(SUnknownFieldType, [DisplayName]);
    end;
    FreeIndexList;
  end;
  Offset := 0;
{$IFDEF RX_D4}
  inherited InitFieldDefsFromFields;
  { Calculate fields offsets }
  ReallocMem(FOffsets, FieldDefList.Count * SizeOf(Word));
  for I := 0 to FieldDefList.Count - 1 do begin
    FOffsets^[I] := Offset;
    with FieldDefList[I] do begin
      if (DataType in ftSupported - ftBlobTypes) then
        Inc(Offset, CalcFieldLen(DataType, Size) + 1);
    end;
  end;
{$ELSE}
  { Create FieldDefs from persistent fields if needed }
  if FieldDefs.Count = 0 then
    for I := 0 to FieldCount - 1 do begin
      with Fields[I] do
        if (FieldKind = fkData) then
          FieldDefs.Add(FieldName, DataType, Size, Required);
    end;
  { Calculate fields offsets }
  ReallocMem(FOffsets, FieldDefs.Count * SizeOf(Word));
  for I := 0 to FieldDefs.Count - 1 do begin
    FOffsets^[I] := Offset;
    with FieldDefs[I] do begin
      if (DataType in ftSupported - ftBlobTypes) then
        Inc(Offset, CalcFieldLen(DataType, Size) + 1);
    end;
  end;
{$ENDIF}
end;

function TRxMemoryData.FindFieldData(Buffer: Pointer; Field: TField): Pointer;
var
  Index: Integer;
begin
{$IFDEF RX_D4}
  Index := FieldDefList.IndexOf(Field.FullName);
{$ELSE}
  Index := FieldDefs.IndexOf(Field.FieldName);
{$ENDIF}
  if (Index >= 0) and (Buffer <> nil) and
{$IFDEF RX_D4}
    (FieldDefList[Index].DataType in ftSupported - ftBlobTypes) then
{$ELSE}
    (FieldDefs[Index].DataType in ftSupported - ftBlobTypes) then
{$ENDIF}
    Result := (PChar(Buffer) + FOffsets[Index])
  else Result := nil;
end;

{ Buffer Manipulation }

function TRxMemoryData.CalcRecordSize: Integer;
var
  I: Integer;
begin
  Result := 0;
  for I := 0 to FieldDefs.Count - 1 do
    CalcDataSize(FieldDefs[I], Result);
end;

procedure TRxMemoryData.InitBufferPointers(GetProps: Boolean);
begin
  if GetProps then FRecordSize := CalcRecordSize;
  FBookmarkOfs := FRecordSize + CalcFieldsSize;
  FBlobOfs := FBookmarkOfs + SizeOf(TMemBookmarkInfo);
  FRecBufSize := FBlobOfs + BlobFieldCount * SizeOf(Pointer);
end;

procedure TRxMemoryData.ClearRecords;
begin
  while FRecords.Count > 0 do TObject(FRecords.Last).Free;
  FLastID := Low(Integer);
  FRecordPos := -1;
end;

function TRxMemoryData.AllocRecordBuffer: PChar;
begin
  Result := StrAlloc(FRecBufSize);
  if BlobFieldCount > 0 then
    Initialize(PMemBlobArray(Result + FBlobOfs)[0], BlobFieldCount);
end;

procedure TRxMemoryData.FreeRecordBuffer(var Buffer: PChar);
begin
  if BlobFieldCount > 0 then
    Finalize(PMemBlobArray(Buffer + FBlobOfs)[0], BlobFieldCount);
  StrDispose(Buffer);
  Buffer := nil;
end;

procedure TRxMemoryData.ClearCalcFields(Buffer: PChar);
begin
  FillChar(Buffer[FRecordSize], CalcFieldsSize, 0);
end;

procedure TRxMemoryData.InternalInitRecord(Buffer: PChar);
var
  I: Integer;
begin
  FillChar(Buffer^, FBlobOfs, 0);
  for I := 0 to BlobFieldCount - 1 do
    PMemBlobArray(Buffer + FBlobOfs)[I] := '';
end;

procedure TRxMemoryData.InitRecord(Buffer: PChar);
begin
  inherited InitRecord(Buffer);
  with PMemBookmarkInfo(Buffer + FBookmarkOfs)^ do begin
    BookmarkData := Low(Integer);
    BookmarkFlag := bfInserted;
  end;
end;

function TRxMemoryData.GetCurrentRecord(Buffer: PChar): Boolean;
begin
  Result := False;
  if not IsEmpty and (GetBookmarkFlag(ActiveBuffer) = bfCurrent) then begin
    UpdateCursorPos;
    if (FRecordPos >= 0) and (FRecordPos < RecordCount) then begin
      Move(Records[FRecordPos].Data^, Buffer^, FRecordSize);
      Result := True;
    end;
  end;
end;

procedure TRxMemoryData.RecordToBuffer(Rec: TMemoryRecord; Buffer: PChar);
var
  I: Integer;
begin
  Move(Rec.Data^, Buffer^, FRecordSize);
  with PMemBookmarkInfo(Buffer + FBookmarkOfs)^ do begin
    BookmarkData := Rec.ID;
    BookmarkFlag := bfCurrent;
  end;
  for I := 0 to BlobFieldCount - 1 do
    PMemBlobArray(Buffer + FBlobOfs)[I] := PMemBlobArray(Rec.FBlobs)[I];
  GetCalcFields(Buffer);
end;

function TRxMemoryData.GetRecord(Buffer: PChar; GetMode: TGetMode;
  DoCheck: Boolean): TGetResult;
var
  Accept: Boolean;
begin
  Result := grOk;
  Accept := True;
  case GetMode of
    gmPrior:
      if FRecordPos <= 0 then begin
        Result := grBOF;
        FRecordPos := -1;
      end
      else begin
        repeat
          Dec(FRecordPos);
          if Filtered then Accept := RecordFilter;
        until Accept or (FRecordPos < 0);
        if not Accept then begin
          Result := grBOF;
          FRecordPos := -1;
        end;
      end;
    gmCurrent:
      if (FRecordPos < 0) or (FRecordPos >= RecordCount) then
        Result := grError
      else if Filtered then begin
        if not RecordFilter then Result := grError;
      end;
    gmNext:
      if FRecordPos >= RecordCount - 1 then Result := grEOF
      else begin
        repeat
          Inc(FRecordPos);
          if Filtered then Accept := RecordFilter;
        until Accept or (FRecordPos > RecordCount - 1);
        if not Accept then begin
          Result := grEOF;
          FRecordPos := RecordCount - 1;
        end;
      end;
  end;
  if Result = grOk then RecordToBuffer(Records[FRecordPos], Buffer)
  else if (Result = grError) and DoCheck then Error(SMemNoRecords);
end;

function TRxMemoryData.GetRecordSize: Word;
begin
  Result := FRecordSize;
end;

function TRxMemoryData.GetActiveRecBuf(var RecBuf: PChar): Boolean;
begin
  case State of
    dsBrowse:
      if IsEmpty then RecBuf := nil
      else RecBuf := ActiveBuffer;
    dsEdit, dsInsert: RecBuf := ActiveBuffer;
    dsCalcFields: RecBuf := CalcBuffer;
    dsFilter: RecBuf := TempBuffer;
    else RecBuf := nil;
  end;
  Result := RecBuf <> nil;
end;

function TRxMemoryData.GetFieldData(Field: TField; Buffer: Pointer): Boolean;
var
  RecBuf, Data: PChar;
{$IFDEF RX_D5}
  VarData: Variant;
{$ENDIF}
begin
  Result := False;
  if not GetActiveRecBuf(RecBuf) then Exit;
  if Field.FieldNo > 0 then begin
    Data := FindFieldData(RecBuf, Field);
    if Data <> nil then begin
      Result := Boolean(Data[0]);
      Inc(Data);
      if Field.DataType in [ftString {$IFDEF RX_D4}, ftFixedChar,
        ftWideString {$ENDIF} {$IFDEF RX_D5}, ftGuid {$ENDIF}] then
        Result := Result and (StrLen(Data) > 0);
      if Result and (Buffer <> nil) then
{$IFDEF RX_D5}
        if Field.DataType = ftVariant then begin
          VarData := PVariant(Data)^;
          PVariant(Buffer)^ := VarData;
        end else
{$ENDIF}
        Move(Data^, Buffer^, CalcFieldLen(Field.DataType, Field.Size));
    end;
  end
  else begin
    if State in [dsBrowse, dsEdit, dsInsert, dsCalcFields] then begin
      Inc(RecBuf, FRecordSize + Field.Offset);
      Result := Boolean(RecBuf[0]);
      if Result and (Buffer <> nil) then
        Move(RecBuf[1], Buffer^, Field.DataSize);
    end;
  end;
end;

procedure TRxMemoryData.SetFieldData(Field: TField; Buffer: Pointer);
var
  RecBuf, Data: PChar;
{$IFDEF RX_D5}
  VarData: Variant;
{$ENDIF}
begin
  if not (State in dsWriteModes) then Error(SNotEditing);
  GetActiveRecBuf(RecBuf);
  with Field do begin
    if FieldNo > 0 then
    begin
      if State in [dsCalcFields, dsFilter] then Error(SNotEditing);
      if ReadOnly and not (State in [dsSetKey, dsFilter]) then
        ErrorFmt(SFieldReadOnly, [DisplayName]);
      Validate(Buffer);
      if FieldKind <> fkInternalCalc then begin
        Data := FindFieldData(RecBuf, Field);
        if Data <> nil then begin
{$IFDEF RX_D5}
          if DataType = ftVariant then begin
            if Buffer <> nil then
              VarData := PVariant(Buffer)^
            else
              VarData := EmptyParam;
            Boolean(Data[0]) := LongBool(Buffer) and not
              (VarIsNull(VarData) or VarIsEmpty(VarData));
            if Boolean(Data[0]) then begin
              Inc(Data);
              PVariant(Data)^ := VarData;
            end
            else FillChar(Data^, CalcFieldLen(DataType, Size), 0);
          end else
{$ENDIF}
          begin
            Boolean(Data[0]) := LongBool(Buffer);
            Inc(Data);
            if LongBool(Buffer) then
              Move(Buffer^, Data^, CalcFieldLen(DataType, Size))
            else FillChar(Data^, CalcFieldLen(DataType, Size), 0);
          end;
        end;
      end;
    end else {fkCalculated, fkLookup}
    begin
      Inc(RecBuf, FRecordSize + Offset);
      Boolean(RecBuf[0]) := LongBool(Buffer);
      if Boolean(RecBuf[0]) then Move(Buffer^, RecBuf[1], DataSize);
    end;
    if not (State in [dsCalcFields, dsFilter, dsNewValue]) then
      DataEvent(deFieldChange, Longint(Field));
  end;
end;

{ Filter }

procedure TRxMemoryData.SetFiltered(Value: Boolean);
begin
  if Active then begin
    CheckBrowseMode;
    if Filtered <> Value then begin
      inherited SetFiltered(Value);
      First;
    end;
  end
  else inherited SetFiltered(Value);
end;

procedure TRxMemoryData.SetOnFilterRecord(const Value: TFilterRecordEvent);
begin
  if Active then begin
    CheckBrowseMode;
    inherited SetOnFilterRecord(Value);
    if Filtered then First;
  end
  else inherited SetOnFilterRecord(Value);
end;

function TRxMemoryData.RecordFilter: Boolean;
var
  SaveState: TDataSetState;
begin
  Result := True;
  if Assigned(OnFilterRecord) then begin
    if (FRecordPos >= 0) and (FRecordPos < RecordCount) then begin
      SaveState := SetTempState(dsFilter);
      try
        RecordToBuffer(Records[FRecordPos], TempBuffer);
        OnFilterRecord(Self, Result);
      except
        Application.HandleException(Self);
      end;
      RestoreState(SaveState);
    end
    else Result := False;
  end;
end;

{ Blobs }

function TRxMemoryData.GetBlobData(Field: TField; Buffer: PChar): TMemBlobData;
begin
  Result := PMemBlobArray(Buffer + FBlobOfs)[Field.Offset];
end;

procedure TRxMemoryData.SetBlobData(Field: TField; Buffer: PChar;
  Value: TMemBlobData);
begin
  if (Buffer = ActiveBuffer) then begin
    if State = dsFilter then Error(SNotEditing);
    PMemBlobArray(Buffer + FBlobOfs)[Field.Offset] := Value;
  end;
end;

procedure TRxMemoryData.CloseBlob(Field: TField);
begin
  if (FRecordPos >= 0) and (FRecordPos < FRecords.Count) and
    (State = dsEdit) then
    PMemBlobArray(ActiveBuffer + FBlobOfs)[Field.Offset] := 
      PMemBlobArray(Records[FRecordPos].FBlobs)[Field.Offset]
  else PMemBlobArray(ActiveBuffer + FBlobOfs)[Field.Offset] := '';
end;

function TRxMemoryData.CreateBlobStream(Field: TField; Mode: TBlobStreamMode): TStream;
begin
  Result := TMemBlobStream.Create(Field as TBlobField, Mode);
end;

{ Bookmarks }

function TRxMemoryData.BookmarkValid(Bookmark: TBookmark): Boolean;
begin
  Result := FActive and (TBookmarkData(Bookmark^) > Low(Integer)) and
    (TBookmarkData(Bookmark^) <= FLastID);
end;

function TRxMemoryData.CompareBookmarks(Bookmark1, Bookmark2: TBookmark): Integer;
begin
  if (Bookmark1 = nil) and (Bookmark2 = nil) then Result := 0
  else if (Bookmark1 <> nil) and (Bookmark2 = nil) then Result := 1
  else if (Bookmark1 = nil) and (Bookmark2 <> nil) then Result := -1
  else if TBookmarkData(Bookmark1^) > TBookmarkData(Bookmark2^) then
    Result := 1
  else if TBookmarkData(Bookmark1^) < TBookmarkData(Bookmark2^) then
    Result := -1
  else Result := 0;
end;

procedure TRxMemoryData.GetBookmarkData(Buffer: PChar; Data: Pointer);
begin
  Move(PMemBookmarkInfo(Buffer + FBookmarkOfs)^.BookmarkData, Data^,
    SizeOf(TBookmarkData));
end;

procedure TRxMemoryData.SetBookmarkData(Buffer: PChar; Data: Pointer);
begin
  Move(Data^, PMemBookmarkInfo(Buffer + FBookmarkOfs)^.BookmarkData,
    SizeOf(TBookmarkData));
end;

function TRxMemoryData.GetBookmarkFlag(Buffer: PChar): TBookmarkFlag;
begin
  Result := PMemBookmarkInfo(Buffer + FBookmarkOfs)^.BookmarkFlag;
end;

procedure TRxMemoryData.SetBookmarkFlag(Buffer: PChar; Value: TBookmarkFlag);
begin
  PMemBookmarkInfo(Buffer + FBookmarkOfs)^.BookmarkFlag := Value;
end;

procedure TRxMemoryData.InternalGotoBookmark(Bookmark: TBookmark);
var
  Rec: TMemoryRecord;
  SavePos: Integer;
  Accept: Boolean;
begin
  Rec := FindRecordID(TBookmarkData(Bookmark^));
  if Rec <> nil then begin
    Accept := True;
    SavePos := FRecordPos;
    try
      FRecordPos := Rec.Index;
      if Filtered then Accept := RecordFilter;
    finally
      if not Accept then FRecordPos := SavePos;
    end;
  end;
end;

{ Navigation }

procedure TRxMemoryData.InternalSetToRecord(Buffer: PChar);
begin
  InternalGotoBookmark(@PMemBookmarkInfo(Buffer + FBookmarkOfs)^.BookmarkData);
end;

procedure TRxMemoryData.InternalFirst;
begin
  FRecordPos := -1;
end;

procedure TRxMemoryData.InternalLast;
begin
  FRecordPos := FRecords.Count;
end;

{ Data Manipulation }

procedure TRxMemoryData.AssignMemoryRecord(Rec: TMemoryRecord; Buffer: PChar);
var
  I: Integer;
begin
  Move(Buffer^, Rec.Data^, FRecordSize);
  for I := 0 to BlobFieldCount - 1 do
    PMemBlobArray(Rec.FBlobs)[I] := PMemBlobArray(Buffer + FBlobOfs)[I];
end;

procedure TRxMemoryData.SetMemoryRecordData(Buffer: PChar; Pos: Integer);
var
  Rec: TMemoryRecord;
begin
  if State = dsFilter then Error(SNotEditing);
  Rec := Records[Pos];
  AssignMemoryRecord(Rec, Buffer);
end;

procedure TRxMemoryData.SetAutoIncFields(Buffer: PChar);
var
  I, Count: Integer;
  Data: PChar;
begin
  Count := 0;
  for I := 0 to FieldCount - 1 do
    if (Fields[I].FieldKind in fkStoredFields) and
      (Fields[I].DataType = ftAutoInc) then
    begin
      Data := FindFieldData(Buffer, Fields[I]);
      if Data <> nil then begin
        Boolean(Data[0]) := True;
        Inc(Data);
        Move(FAutoInc, Data^, SizeOf(Longint));
        Inc(Count);
      end;
    end;
  if Count > 0 then Inc(FAutoInc);
end;

procedure TRxMemoryData.InternalAddRecord(Buffer: Pointer; Append: Boolean);
var
  RecPos: Integer;
  Rec: TMemoryRecord;
begin
  if Append then begin
    Rec := AddRecord;
    FRecordPos := FRecords.Count - 1;
  end
  else begin
    if FRecordPos = -1 then RecPos := 0
    else RecPos := FRecordPos;
    Rec := InsertRecord(RecPos);
    FRecordPos := RecPos;
  end;