database – 如何在运行时更改Clientdataset字段数据类型

想法是查询相关的表模式;获取实际的fileds数据类型;并通过从DataSet取消附加并添加新的匹配持久字段来“更改”持久字段类型：

// TData class    
procedure TData.DataModuleCreate(Sender: TObject);
var
  I: Integer;
begin
  for I := 0 to ComponentCount - 1 do
    if (Components[I] is TCustomADODataSet) then
      DataSetPrepareMemoFields(TDataSet(Components[I]));
end;

procedure TData.DataSetPrepareMemoFields(DataSet: TDataSet);
var
  Fld: TField;
  I: Integer;
  FldName,CompName: string;
  AOwner: TComponent;
begin
  // Here you need to query the actual table schema from the database 
  // e.g. ADOConnection.GetFieldNames and act accordingly

  // check which DataSet you need to change
  // if (DataSet = dsOrders) or ... then... 

  if DataSet.FieldList.Count > 0 then
    for I := DataSet.FieldList.Count - 1 downto 0 do 
    begin
      if DataSet.FieldList.Fields[I].ClassNameIs('TMemoField') and (DataSet.FieldList.Fields[I].FieldKind = fkData) then 
      begin
        // save TMemoField properties
        AOwner := DataSet.FieldList[I].Owner;
        CompName := DataSet.FieldList[I].Name;
        FldName := DataSet.FieldList.Fields[I].FieldName;
        // dispose of TMemoField
        DataSet.FieldList[I].DataSet := nil; // Un-Attach it from the DataSet
        // create TWideADOMemoField instead
        Fld := TWideADOMemoField.Create(AOwner); // Create new persistent Filed instead 
        Fld.Name := CompName + '_W';
        Fld.FieldName := FldName;
        Fld.DataSet := DataSet;
      end;
    end;
end;

也就是说,在我解决了这个问题之后,我再也没有使用过持久字段了.我的所有字段都是在运行时生成的.包括计算/查找/内部字段.