FrankKanBear commented on code in PR #10:
URL:
https://github.com/apache/ignite-nodejs-thin-client/pull/10#discussion_r3372391171
##########
src/Cursor.ts:
##########
@@ -74,8 +73,13 @@ export abstract class BaseCursor<T> {
* @return {boolean} - true if more cache entries are available, false
otherwise.
*/
hasMore(): boolean {
+ // _buffer is set on a freshly-opened cursor and holds the first page
of
+ // results before _getValues() has been called for the first time.
+ // Without this check, hasMore() incorrectly returns false on a new
cursor
+ // because _hasNext starts as false and _values starts as null.
return this._hasNext ||
- this._values && this._valueIndex < this._values.length;
+ (this._values != null && this._valueIndex < this._values.length) ||
+ this._buffer != null;
Review Comment:
Good catch — this is correct. With || this._buffer != null, a zero-row first
page (rowCount = 0, trailing hasNext = false) makes hasMore() return true while
the next getValue() returns null, so a while (cursor.hasMore()) { … } loop runs
one spurious iteration on any empty result.
Peeking the buffered page's rowCount (and the trailing hasNext when rowCount
=== 0) without consuming it fixes it — MessageBuffer exposes position get/set,
so save → peek → restore is safe and stays synchronous:
if (this._hasNext) {
return true;
}
if (this._values != null && this._valueIndex < this._values.length) {
return true;
}
if (this._buffer != null) {
// Peek the buffered first page without consuming it. A page is
laid out as
// [rowCount:int][rows...][hasNext:bool]; rowCount === 0 with a
trailing
// hasNext === false is an empty result, so hasMore() must be
false here.
const savedPosition = this._buffer.position;
const rowCount = this._buffer.readInteger();
const more = rowCount > 0 || this._buffer.readBoolean();
this._buffer.position = savedPosition;
return more;
}
return false;
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