根据DELTA自动生成SQL语句

上传客户端的CLIENTDATASET.delta到服务器的clientdataset.data，服务端解析clientdataset的数据生成相应的SQL语句。

相对于直接调用datasetprovider.applyupdates()方法提交数据而言，前者的可控性更强，对于某些要求灵活性很强的场合，前者可能是必须的提交方式。

procedure TBaseService.ApplyUpdates(const Delta: OleVariant; TableName, KeyField: WideString);
var
  Flag: Boolean;
begin
  if VarIsNull(Delta) then exit;
  with (FParent as TDataServer2) do
    begin
      cdsDelta.Close;
      cdsDelta.Data := Delta;
      Flag := cdsDelta.FindField('SYS_STATUS') <> nil;
    end; // with
  if Flag then
    InnerApplyUpdates2(TableName, KeyField)
  else
    InnerApplyUpdates(TableName, KeyField);
end;

 

 function vartosql(value: Variant): wideString;
      var
      tmp:widestring;
      begin
         if (varisnull(Value)) or (varisempty(Value)) then
          Result:='NULL'
         else
          case Vartype(value) of
            varDate:
            begin
              tmp := formatDatetime('yyyy-mm-dd hh:mm:ss', VartoDatetime(Value));
              Result:=Quotedstr(tmp);
            end;
            varString,varOlestr:
              Result:=Quotedstr(Trim(Vartostr(Value)));
            varboolean:
            begin
              if Value then
                Result:='1'
              else
                Result:='0';
            end;
            varSmallint,varInteger,varDouble,varShortInt,varInt64,varLongWord,varCurrency:
            begin
              Result:=trim(Vartostr(Value));
            end;
          else
              Result:=Quotedstr(Trim(Vartostr(Value)));
          end;
      end;

procedure TBaseService.InnerApplyUpdates(TableName, KeyField: WideString);
var
  i: integer;
  s1, s2: string;
  CmdStr: string;
  FieldList: TStringList;
begin
  with (FParent as TDataServer2) do
    begin
      FieldList := TStringList.Create;
      Connection.GetFieldNames(TableName, FieldList);
      if not cdsDelta.Active then cdsDelta.Open;
      for i := 1 to FieldList.Count do
        if cdsDelta.FindField(FieldList[i - 1]) <> nil then
          cdsDelta.FindField(FieldList[i - 1]).Tag := 1;
      FieldList.Free;
      if cdsDelta.RecordCount > 0 then
        begin
          cdsDelta.First;
          s1 := '';
          s2 := '';
          while not cdsDelta.Eof do
            begin
              CmdStr := '';
              case cdsDelta.UpdateStatus of
                usUnmodified:
                  begin
                    s2 := VarToSql(cdsDelta[KeyField]);
                  end;
                usModified:
                  begin
                    s1 := '';
                    for i := 1 to cdsDelta.FieldCount do
                     // if (not cdsDelta.Fields[i - 1].IsNull) and (cdsDelta.Fields[i - 1].Tag = 1) then

 if (cdsDelta.Fields[i-1].NewValue <> System.Variants.Unassigned and (cdsDelta.Fields[i - 1].Tag = 1) then
                        begin
                          if s1 = '' then
                            s1 := Trim(cdsDelta.Fields[i - 1].FieldName) + ' = ' + VarToSql(cdsDelta.Fields[i - 1].Value)
                          else
                            s1 := s1 + ',' + Trim(cdsDelta.Fields[i - 1].FieldName) + ' = ' + VarToSql(cdsDelta.Fields[i - 1].Value);
                        end;
                    if s1 <> '' then
                      begin
                        CmdStr := 'Update ' + TableName + ' Set ' + s1 + ' Where ' + KeyField + ' = ' + s2;
                      end;
                  end;
                usInserted:
                  begin
                    s1 := '';
                    s2 := '';
                    for i := 1 to cdsDelta.FieldCount do
                      if (not cdsDelta.Fields[i - 1].IsNull) and (cdsDelta.Fields[i - 1].Tag = 1) then
                        begin
                          if s1 = '' then
                            begin
                              s1 := Trim(cdsDelta.Fields[i - 1].FieldName);
                              s2 := VarToSql(cdsDelta.Fields[i - 1].Value);
                            end
                          else
                            begin
                              s1 := s1 + ',' + Trim(cdsDelta.Fields[i - 1].FieldName);
                              s2 := s2 + ',' + VarToSql(cdsDelta.Fields[i - 1].Value);
                            end;
                        end;
                    if s1 <> '' then
                      begin
                        CmdStr := 'Insert into ' + TableName + '(' + s1 + ') Values (' + s2 + ')';
                      end;
                  end;
                usDeleted:
                  begin
                    s2 := VarToSql(cdsDelta[KeyField]);
                    CmdStr := 'Delete ' + TableName + ' Where ' + KeyField + ' = ' + s2;
                  end;
              end;
              if CmdStr <> '' then Cmd.Execute(CmdStr);
              cdsDelta.Next;
            end;
          cdsDelta.First;
          cdsDelta.EmptyDataSet;
          cdsDelta.Close;
        end;
    end;
end;

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在更新时, 如果新值为Null, 会被漏掉, 解决办法如下:
把usModified中的not Field.IsNull改为Field.NewValue <> System.Variants.Unassigned