How to Sort Records in Delphi DBGrid

Delphi DBGrid is such a powerful component that you're probably using it every day if you're developing data-aware applications. Below, we'll take a look at how to add some more features to your database applications that your users are sure to love.

Following the concepts described in the Beginners Guide to Delphi Database Programming, the examples below use ADO components (AdoQuery/AdoTable connected to ADOConnection, DBGrid connected to AdoQuery over DataSource) to display the records from a database table in a DBGrid component.

All the component names were left as Delphi named them when dropped on the form (DBGrid1, ADOQuery1, AdoTable1, etc.).

Mouse Moves Over DBGrid Title Area

First, let's see how to change the mouse pointer while it moves over the DBGrid title area. All you have to do is add the code to the OnMouseMove event for the DBGrid component.

The code below simply uses the MouseCoord property of the DBGrid component to "calculate" where the mouse pointer is. If it's over the DGBrid title area, the pt.y equals 0, which is the first row in the DBGrid (the title area displaying column/field titles).

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procedure TForm1.DBGrid1MouseMove
 (Sender: TObject; Shift: TShiftState; X, Y: Integer);
var
 pt: TGridcoord;
begin
 pt:= DBGrid1.MouseCoord(x, y);
 if pt.y=0 then
 DBGrid1.Cursor:=crHandPoint
 else
 DBGrid1.Cursor:=crDefault;
end;

Sort on Column Click and Change the Column Title Font

If you're using the ADO approach to Delphi database development, and want to sort the records in the dataset, you need to set the Sort property of your AdoDataset (ADOQuery, AdoTable).

The Sort property is the widestring value indicating the "ORDER BY" part of the standard SQL query. Of course, you do not need to write the SQL query to be able to use the Sort property. Simply set the Sort property to the name of a single field or to a comma-separated list of fields, each following the sort order.

Here's an example:

ADOTable1.Sort := 'Year DESC, ArticleDate ASC'

The OnTitleClick event of the DBGrid component has a Column parameter indicating the Column the user has clicked on. Each Column (object of type TColumn) has a Field property indicating the Field (TField) represented by the Column, and the Field in its FieldName property holds the name of the field in the underlying dataset.

Therefore, to sort an ADO dataset by field/column, a simple line can be used:

with TCustomADODataSet(DBGrid1.DataSource.DataSet) do
Sort := Column.Field.FieldName; // + ' ASC' or ' DESC'

Below is the code for the OnTitleClick even handler that sorts the records by column click. The code, as always, extends the idea.

First, we want to, in some way, mark the column that's currently used for sort order. Next, if we click on a column title and the dataset is already sorted by that column, we want to change the sort order from ASC (ascending) to DESC (descending), and vice versa. Finally, when we sort the dataset by another column, we want to remove the mark from the previously selected column.

For the sake of simplicity, to mark the column that "sorts" the records, we'll simply change the font style of the column title to Bold, and remove it when dataset is sorted using another column.

procedure TForm1.DBGrid1TitleClick(Column: TColumn);
{$J+}const PreviousColumnIndex : integer = -1;
{$J-}
beginif DBGrid1.DataSource.DataSet is TCustomADODataSet thenwith TCustomADODataSet(DBGrid1.DataSource.DataSet) dobegintry
 DBGrid1.Columns[PreviousColumnIndex].title.Font.Style :=
 DBGrid1.Columns[PreviousColumnIndex].title.Font.Style - [fsBold];
 exceptend;
 Column.title.Font.Style := 
 Column.title.Font.Style + [fsBold];
 PreviousColumnIndex := Column.Index;
 if (Pos(Column.Field.FieldName, Sort) = 1)
 and (Pos(' DESC', Sort)= 0) then
 Sort := Column.Field.FieldName + ' DESC'
 else
 Sort := Column.Field.FieldName + ' ASC';
 end;
end;

The above code uses typed constants to preserve the value of the previously "selected" column for sort order.