mORMot Open Source

...
 TSQLProviders = class(TSQLRecord)
  private
    FIntf: UIntPtr;                                                 {What type of interface variable?}
  published
    property Intf: UIntPtr read FIntf write FIntf;
  end;
....
    Intf := TSomeProvider.Create;
   Rec.Intf :=  UIntPtr(Intf);                                            {how to convert interface variable to store in database?}
   FRest.Add(Rec,True);
....
   Provider := ISomeInterface(Rec.Intf).GetProvider;        {how to call the interface method from database?}

procedure TSynBinaryDataSet.InternalInitFieldDefs;
var F: integer;
    DBType: TFieldType;
    FieldList: TStringList;
    i: Integer;
begin
  (*
     If before opening a TSynDBDataset, the field structure (Dataset.FieldDefs)
     was previously defined, we use the length of the fields from this structure
     so as not to cut the length of the text fields TDBedit.Text
  *)

  FieldList := TStringList.Create;
  try
    for i := 0 to FieldDefs.Count - 1 do
      if FieldDefs.Items[i].DataType = ftString then
        FieldList.AddPair(FieldDefs.Items[i].Name, FieldDefs.Items[i].Size.ToString);

    FieldDefs.Clear;
    if fDataAccess=nil then
      exit;
    for F := 0 to fDataAccess.ColumnCount-1 do
      with fDataAccess.Columns[F] do begin
      case ColumnType of
      SynTable.ftInt64:
        DBType := ftLargeint;
      SynTable.ftDate:
        DBType := ftDateTime;
      SynTable.ftUTF8:
        begin
          if ColumnDataSize=0 then
            DBType := ftDefaultMemo
          else
            DBType := ftWideString; // means UnicodeString for Delphi 2009+
        end;
      SynTable.ftBlob:
        DBType := ftBlob;
      SynTable.ftDouble, SynTable.ftCurrency:
        DBType := ftFloat;
      else
        raise EDatabaseError.CreateFmt(
          'GetFieldData ColumnType=%s',[TSQLDBFieldTypeToString(ColumnType)]);
      end;

      if ToInteger(FieldList.Values[ColumnName], i) then
        FieldDefs.Add(UTF8ToString(ColumnName),DBType, i)
      else
        FieldDefs.Add(UTF8ToString(ColumnName),DBType,ColumnDataSize);
    end;
  finally
    FieldList.Free;
  end;
end;

  8: // test TSynDBSQLDataSet / TSynDBDataSet
    if chkViaTClientDataSet.Checked then begin
      ds1.DataSet := TSynDBDataSet.Create(self);

      // ++++  Pre-determine the length of text fields
      TSynDBDataSet(ds1.DataSet).DataSet.FieldDefs.Clear;
      TSynDBDataSet(ds1.DataSet).DataSet.FieldDefs.Add('FirstName', ftString, 30);
      TSynDBDataSet(ds1.DataSet).DataSet.FieldDefs.Add('LastName', ftString, 30);
      // ++++

      TSynDBDataSet(ds1.DataSet).Connection := fProps;
      TSynDBDataSet(ds1.DataSet).CommandText := SQL_PEOPLE;
      //--- Does not affect
      TSynDBDataSet(ds1.DataSet).IgnoreColumnDataSize := true;

      ds1.DataSet.Open;
    end else begin
      ds1.DataSet := TSynDBSQLDataSet.Create(self);
      TSynDBSQLDataSet(ds1.DataSet).Connection := fProps;
      TSynDBSQLDataSet(ds1.DataSet).CommandText := SQL_PEOPLE;
      ds1.DataSet.Open;
    end;
  end;