check count(*)

db/accessor.go

@@ -13,6 +13,6 @@ type Block struct {
 type DBAccessor interface {
 	Migrate() error
 	FindLatestBlocks(mintime int64, limit int) ([]Block, error)
-	GetBlocks(pos1 coords.MapBlockCoords, pos2 coords.MapBlockCoords) ([]Block, error)
+	CountBlocks(pos1 coords.MapBlockCoords, pos2 coords.MapBlockCoords) (int, error)
 	GetBlock(pos coords.MapBlockCoords) (*Block, error)
 }

db/sqlite.go

@@ -85,6 +85,8 @@ func (db *Sqlite3Accessor) GetBlock(pos coords.MapBlockCoords) (*Block, error) {
 		return nil, err
 	}
 
+	defer rows.Close()
+
 	if rows.Next() {
 		var pos int64
 		var data []byte
@@ -103,16 +105,16 @@ func (db *Sqlite3Accessor) GetBlock(pos coords.MapBlockCoords) (*Block, error) {
 }
 
 
-func (db *Sqlite3Accessor) GetBlocks(pos1 coords.MapBlockCoords, pos2 coords.MapBlockCoords) ([]Block, error){
+func (db *Sqlite3Accessor) CountBlocks(pos1 coords.MapBlockCoords, pos2 coords.MapBlockCoords) (int, error){
 
 	poslist := make([]interface{}, 0)
 
 	if pos1.X != pos2.X {
-		return nil, errors.New("x does not line up")
+		return 0, errors.New("x does not line up")
 	}
 
 	if pos1.Z != pos2.Z {
-		return nil, errors.New("z does not line up")
+		return 0, errors.New("z does not line up")
 	}
 
 	minY := pos1.Y
@@ -126,30 +128,27 @@ func (db *Sqlite3Accessor) GetBlocks(pos1 coords.MapBlockCoords, pos2 coords.Map
 		poslist = append(poslist, coords.CoordToPlain(coords.NewMapBlockCoords(pos1.X, y, pos1.Z)))
 	}
 
-	getBlocksQuery := "select pos,data,mtime from blocks b where b.pos in (?" + strings.Repeat(",?", len(poslist)-1) + ")"
+	getBlocksQuery := "select count(*) from blocks b where b.pos in (?" + strings.Repeat(",?", len(poslist)-1) + ")"
 
 	rows, err := db.db.Query(getBlocksQuery, poslist...)
 	if err != nil {
-		return nil, err
+		return 0, err
 	}
 
-	blocklist := make([]Block, 0)
+	defer rows.Close()
 
-	for rows.Next() {
-		var pos int64
-		var data []byte
-		var mtime int64
+	if rows.Next() {
+		var count int
 
-		err = rows.Scan(&pos, &data, &mtime)
+		err = rows.Scan(&count)
 		if err != nil {
-			return nil, err
+			return 0, err
 		}
 
-		mb := convertRows(pos, data, mtime)
-		blocklist = append(blocklist, mb)
+		return count, nil
 	}
 
-	return blocklist, nil
+	return 0, errors.New("No rows returned")
 }
 
 func NewSqliteAccessor(filename string) (*Sqlite3Accessor, error) {

db/sqlite_test.go

@@ -94,13 +94,13 @@ func TestMigrateAndQueryStride(t *testing.T) {
 		panic(err)
 	}
 
-	blocks, err := a.GetBlocks(coords.NewMapBlockCoords(0, -1, 0), coords.NewMapBlockCoords(0, 10, 0))
+	count, err := a.CountBlocks(coords.NewMapBlockCoords(0, -1, 0), coords.NewMapBlockCoords(0, 10, 0))
 
 	if err != nil {
 		panic(err)
 	}
 
-	if blocks == nil {
+	if count == 0 {
 		t.Fatal("no data")
 	}
 

main.go

@@ -75,7 +75,7 @@ func main() {
 		panic(err)
 	}
 
-	tr := tilerenderer.NewTileRenderer(r, tdb, layerconfig.DefaultLayers)
+	tr := tilerenderer.NewTileRenderer(r, tdb, a, layerconfig.DefaultLayers)
 
 	initialrenderer.Render(tr, layerconfig.DefaultLayers)
 

tilerenderer/renderer.go

@@ -7,6 +7,7 @@ import (
 	"bytes"
 	"image/png"
 	"image/draw"
+	"mapserver/db"
 	"mapserver/coords"
 	"mapserver/mapblockrenderer"
 	"mapserver/layerconfig"
@@ -18,16 +19,19 @@ type TileRenderer struct {
 	mapblockrenderer *mapblockrenderer.MapBlockRenderer
 	layers []layerconfig.Layer
 	tdb tiledb.DBAccessor
+	dba db.DBAccessor
 }
 
 func NewTileRenderer(mapblockrenderer *mapblockrenderer.MapBlockRenderer,
 	tdb tiledb.DBAccessor,
+	dba db.DBAccessor,
 	layers []layerconfig.Layer) *TileRenderer {
 
 	return &TileRenderer{
 		mapblockrenderer: mapblockrenderer,
 		layers: layers,
 		tdb: tdb,
+		dba: dba,
 	}
 }
 
@@ -97,6 +101,16 @@ func (tr *TileRenderer) RenderImage(tc coords.TileCoords) (*image.NRGBA, error)
 		mbr.Pos1.Y = layer.From
 		mbr.Pos2.Y = layer.To
 
+		count, err := tr.dba.CountBlocks(mbr.Pos1, mbr.Pos2)
+
+		if err != nil {
+			return nil, err
+		}
+
+		if count == 0 {
+			return nil, nil
+		}
+
 		return tr.mapblockrenderer.Render(mbr.Pos1, mbr.Pos2)
 	}
 

tilerenderer/renderer_test.go

@@ -52,7 +52,7 @@ func TestTileRender(t *testing.T) {
 	tdb, _ := tiledb.NewSqliteAccessor(tiletmpfile.Name())
 	tdb.Migrate()
 
-  tr := NewTileRenderer(r, tdb, layerconfig.DefaultLayers)
+  tr := NewTileRenderer(r, tdb, a, layerconfig.DefaultLayers)
 
   if tr == nil {
     panic("no renderer")