Teach Yourself Borland C++ in 14 Days - portal

446 Day 12
Note that you can double-click MasterFields to invoke C++Builder’s Field Link Designer,
which enables you to establish master/detail relationships visually.
Setting the Active property to true is identical to calling the TDataset’s Open method—it
opens the TDataset. Likewise, setting Active to false is the same as calling the TDataset’s
Close method—it closes the TDataset.
You can check the current status of a TDataset with the State property. It will have one of
the following values:
■ dsInactive—The TDataset is closed.
■ dsBrowse—The TDataset is in Browse mode. The TDataset can be navigated, but
changes can’t be made to the data until State is switched to dsEdit.
■ dsEdit—The TDataset is in EUdit mode and allows changes to the data.
■ dsInsert—The TDataset is in Insert mode.
■ dsSetKey—The TDataset is in SetKey mode because SetKey has just been called.
When values are assigned to columns while in this mode, they are interpreted as
search values. A subsequent GotoKey will search for a record using these values.
■ dsCalcFields—The OnCalcFields event handler is being called.
Tasks
The First method moves the current record pointer (also known as the cursor) to the top
of the TDataset, and the Last method moves to the bottom. The Prior and Next methods
move to the previous and next rows, respectively. Use the MoveBy method to move a number
of rows forward or backward from the current row.
The SetKey, FindKey, GotoKey, FindNearest, and GotoNearest methods can be used to search
the TDataset for a given set of field values.
You use the Bof property to determine whether the TDataset cursor is at its beginning. You
use the Eof property to determine whether the cursor has reached the TDataset’s end. These
two properties can be useful in looping through the rows in a TDataset. For example, here’s
a simple routine that loops through a table’s rows, displaying a field from each as it goes:
Table1->First();
while (!(Table1->Eof)) {
ShowMessage(“Category is: “+Table1->FieldByName(“Category”)->Value);
Table1->Next();
}