Delphi FireDAC 下的 Sqlite（十） 使用 R-Tree 搜索

R-Tree 主要用于三维空间的搜索, 据说这种搜索算法非常之快, 哪怕百万条记录也是眨眼间的事! SQLite 支持 1-5 维, FireDAC 也提供了 TFDSQLiteRTree 控件以方便定义回调函数. 为了简单, 我用二维表进行了成功的测试. 建立 R-Tree 表(索引)时需要使用特定语法, 譬如: FDConnection1.ExecSQL('CREATE VIRTUAL TABLE MyRTreeTable USING rtree(Id, minX, maxX, minY, maxY)'); //必须是 VIRTUAL 表 //USING rtree, 是必须的; 也可以是 USING rtree_i32 //Id, minX, maxX, minY, maxY; 这是 ID 与二维空间的数据, 这里无需指定参数类型; 因为参数类型是内定的: Id 是 64 位无符号整形(且是主键), 后面的数据是 32 位浮点 //如果使用 rtree_i32 定义, 后面的数据则都是 32 为整形; 另外如果指定了 SQLITE_RTREE_INT_ONLY 参数, 无论怎么定义, 内部都用整形计算.

为此我做了两个例子, 第一个例子先没有使用 TFDSQLiteRTree(也就是没用回调). 本例除了使用 TFDConnection, TFDPhysSQLiteDriverLink, TFDGUIxWaitCursor, TDataSource, TDBGrid 外, 还有一个 TPaintBox, 用于绘图和点击测试, 用到它的 OnPaint 和 OnMouseUp 事件. 可把下面代码直接贴在空白窗体上, 以快速完成窗体设计: object PaintBox1: TPaintBox Left = 408 Top = 16 Width = 617 Height = 473 OnMouseUp = PaintBox1MouseUp OnPaint = PaintBox1Paint end object DBGrid1: TDBGrid Left = 0 Top = 0 Width = 393 Height = 503 Align = alLeft DataSource = DataSource1 TabOrder = 0 TitleFont.Charset = DEFAULT_CHARSET TitleFont.Color = clWindowText TitleFont.Height = -11 TitleFont.Name = 'Tahoma' TitleFont.Style = [] end object FDConnection1: TFDConnection Left = 34 Top = 24 end object FDPhysSQLiteDriverLink1: TFDPhysSQLiteDriverLink Left = 143 Top = 24 end object FDGUIxWaitCursor1: TFDGUIxWaitCursor Provider = 'Forms' Left = 260 Top = 24 end object FDQuery1: TFDQuery Connection = FDConnection1 Left = 32 Top = 88 end object DataSource1: TDataSource DataSet = FDQuery1 Left = 132 Top = 88 end object FDSQLiteRTree1: TFDSQLiteRTree DriverLink = FDPhysSQLiteDriverLink1 Left = 256 Top = 96 end

代码:

var VBitmap: TBitmap; //当做内存画布procedure TForm1.FormCreate(Sender: TObject);
const
  W = 50; H = 30;
var
  i,x,y,x1,x2,y1,y2: Integer;
begin
  FDConnection1.Params.Add('DriverID=SQLite');
  FDConnection1.ExecSQL('CREATE VIRTUAL TABLE MyRTreeTable USING rtree(Id, minX, maxX, minY, maxY)'); //建表
  FDConnection1.Connected := True;

  {为数据库添加模拟数据}
  FDConnection1.StartTransaction;
  tryfor i := 0to100dobegin  x := Random(PaintBox1.Width);
      y := Random(PaintBox1.Height);
      FDConnection1.ExecSQL('INSERT INTO MyRTreeTable VALUES(:id, :x1, :x2, :y1, :y2)', [i, x, x+W, y, y+H]);end;
    FDConnection1.Commit;
  exceptFDConnection1.Rollback;
  end;

  {呈现}
  FDQuery1.Open('SELECT * FROM MyRTreeTable ORDER BY Id');
  for i := 0to DBGrid1.Columns.Count - 1do DBGrid1.Columns[i].Width := 66; //默认的网格列太宽了, 处理一下

  {根据刚刚添加的数据绘制一张内存图片}
  VBitmap := TBitmap.Create;
  VBitmap.SetSize(PaintBox1.Width, PaintBox1.Height);
  VBitmap.Canvas.Brush.Color := clWhite;
  VBitmap.Canvas.FillRect(Rect(0, 0, VBitmap.Width, VBitmap.Height));

  FDQuery1.First;
  whilenot FDQuery1.Eof do
  beginx1 := FDQuery1.Fields[1].AsInteger;
    x2 := FDQuery1.Fields[2].AsInteger;
    y1 := FDQuery1.Fields[3].AsInteger;
    y2 := FDQuery1.Fields[4].AsInteger;
    VBitmap.Canvas.Brush.Color := Random($EEEEEE);
    VBitmap.Canvas.FillRect(Rect(x1, y1, x2, y2));
    FDQuery1.Next;
  end;
end;

{在 OnMouseUp 事件中执行了 R-Tree 搜索}procedure TForm1.PaintBox1MouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
var
  i: Integer;
begin
  Caption := Format('%d, %d', [X, Y]);
  FDQuery1.Open('SELECT * FROM MyRTreeTable WHERE minX <= :X AND maxX > :X AND minY <= :Y AND maxY > :Y', [X,Y]); //[X,X,Y,Y] ?
  for i := 0to DBGrid1.Columns.Count - 1do DBGrid1.Columns[i].Width := 66; //这行只为缩小列宽end;

{呈现前面绘制的内存图片}procedure TForm1.PaintBox1Paint(Sender: TObject);
begin
  PaintBox1.Canvas.Draw(0, 0, VBitmap);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  VBitmap.Free;
end;

测试效果图:

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， width
， end
left
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