v0.0.547 allow calling ListWithCount with pageSize=0

wmo/queryList.go

@@ -215,17 +215,44 @@ func (c *Coll[TData]) Count(ctx context.Context, filter ct.RawFilter) (int64, er
 }
 
 func (c *Coll[TData]) ListWithCount(ctx context.Context, filter ct.Filter, pageSize *int, inTok ct.CursorToken) ([]TData, ct.CursorToken, int64, error) {
-	// NOTE: Possible optimization: Cache count in CursorToken, then fetch count only on first page.
-	count, err := c.Count(ctx, filter)
-	if err != nil {
-		return nil, nil, 0, err
-	}
 
-	data, token, err := c.List(ctx, filter, pageSize, inTok)
-	if err != nil {
-		return nil, nil, 0, err
+	if pageSize != nil && *pageSize == 0 {
+
+		// fast track, we return an empty list and do not advance the cursor token
+
+		count, err := c.Count(ctx, filter)
+		if err != nil {
+			return nil, nil, 0, err
+		}
+
+		return make([]TData, 0), inTok, count, nil
+
+	} else if pageSize == nil && inTok.IsStart() {
+
+		// fast track, we simply return len(entries) for count (we query all anyway)
+
+		data, token, err := c.List(ctx, filter, pageSize, inTok)
+		if err != nil {
+			return nil, nil, 0, err
+		}
+
+		return data, token, int64(len(data)), nil
+
+	} else {
+
+		count, err := c.Count(ctx, filter)
+		if err != nil {
+			return nil, nil, 0, err
+		}
+
+		data, token, err := c.List(ctx, filter, pageSize, inTok)
+		if err != nil {
+			return nil, nil, 0, err
+		}
+
+		return data, token, count, nil
+
 	}
-	return data, token, count, nil
 }
 
 func (c *Coll[TData]) ListAllIDs(ctx context.Context, filter ct.RawFilter) ([]string, error) {