如何复制包含其计算字段的Delphi TTable？

Question

I have defined a Delphi TTable object with calculated fields, and it is used in a grid on a form. I would like to make a copy of the TTable object, including the calculated fields, open that copy, do some changes to the data with the copy, close the copy, and then refresh the original copy and thusly the grid view. Is there an easy way to get a copy of a TTable object to be used in such a way?

The ideal answer would be one that solves the problem as generically as possible, ie, a way of getting something like this:

newTable:=getACopyOf(existingTable);

Answer 1

You can use the TBatchMove component to copy a table and its structure.

Set the Mode property to specify the desired operation. The Source and Destination properties indicate the datasets whose records are added, deleted, or copied. The online help has additional details.

(Although I reckon you should investigate a TClientDataSet approach - it's certainly more scalable and faster).

Answer 2

Let me propose several things:

Let us suppose that you want to make changes programmatically. You could then use DisableControls and EnableControls methods of the TTable to disallow screen updates during that time.

If you want to have two screens with the same data (fe to compare data during online changes), you could actually create the same screen twice, with the TTable object being on the screen itself. It will have the exact same configuration (but not carry over previously made changes on the first screen but read the data from the database). Changes made on one screen will not be automatically refreshed on the other.

Another way: Try using TDataSetProvider with TTable as Dataset (source) feeding a TClientDataSet. ApplyUpdates would feed back the changes to the TTable. Since the calculated fields are read only, they are not affected. (untested, but should work)

Answer 3

You should be able to select the table on the form, copy it using Ctrl-C, then paste it into any text editor. You will get the text version of the object's properties which you can then edit as needed. When you are done, select all the text again and you can copy it to the clipboard and paste it back onto a form.

Answer 4

I believe that the second approach (TClientDataset) is probably the best method to use in this scenario. An alternative would be to use a memory table ( kbmMemTable for instance). Either way, you would clone your original table and then after making your changes loop thru the memory version of your dataset and update your original table.