WilliamSong11 commented on a change in pull request #2732:
URL: https://github.com/apache/iotdb/pull/2732#discussion_r582504539
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File path: server/src/main/java/org/apache/iotdb/db/metadata/MTree.java
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@@ -1170,6 +1170,76 @@ private void findChildNodePathInNextLevel(
}
}
+ /**
+ * Get child node in the next level of the given path.
+ *
+ * <p>e.g., MTree has [root.sg1.d1.s1, root.sg1.d1.s2, root.sg1.d2.s1] given
path = root.sg1,
+ * return [d1, d2]
+ *
+ * <p>e.g., MTree has [root.sg1.d1.s1, root.sg1.d1.s2, root.sg1.d2.s1] given
path = root.sg1.d1
+ * return [s1, s2]
+ *
+ * @return All child nodes' seriesPath(s) of given seriesPath.
+ */
+ Set<String> getChildNodeInNextLevel(PartialPath path) throws
MetadataException {
+ String[] nodes = path.getNodes();
+ if (nodes.length == 0 || !nodes[0].equals(root.getName())) {
+ throw new IllegalPathException(path.getFullPath());
+ }
+ Set<String> childNodes = new TreeSet<>();
+ findChildNodeInNextLevel(root, nodes, 1, "", childNodes, nodes.length + 1);
+ return childNodes;
+ }
+
+ /**
+ * Traverse the MTree to match all child node path in next level
+ *
+ * @param node the current traversing node
+ * @param nodes split the prefix path with '.'
+ * @param idx the current index of array nodes
+ * @param parent store the node string having traversed
+ * @param res store all matched device names
+ * @param length expected length of path
+ */
+ @SuppressWarnings("squid:S3776") // Suppress high Cognitive Complexity
warning
+ private void findChildNodeInNextLevel(
+ MNode node, String[] nodes, int idx, String parent, Set<String> res, int
length) {
+ if (node == null) {
+ return;
+ }
+ String nodeReg = MetaUtils.getNodeRegByIdx(idx, nodes);
+ if (!nodeReg.contains(PATH_WILDCARD)) {
+ if (idx == length) {
+ res.add(node.getName());
+ } else {
+ findChildNodeInNextLevel(
+ node.getChild(nodeReg),
+ nodes,
+ idx + 1,
+ parent + node.getName() + PATH_SEPARATOR,
+ res,
+ length);
+ }
+ } else {
+ if (node.getChildren().size() > 0) {
+ for (MNode child : node.getChildren().values()) {
+ if (!Pattern.matches(nodeReg.replace("*", ".*"), child.getName())) {
+ continue;
+ }
+ if (idx == length) {
+ res.add(node.getName());
+ } else {
+ findChildNodeInNextLevel(
+ child, nodes, idx + 1, parent + node.getName() +
PATH_SEPARATOR, res, length);
+ }
+ }
+ } else if (idx == length) {
+ String nodeName = node.getName();
+ res.add(nodeName);
+ }
Review comment:
Thank you for your reply
 I've run some local tests and the results seem to be in line with
expectations
  1、Local client testing
IoTDB> SET STORAGE GROUP TO root.gsxgt
SET STORAGE GROUP TO root.gsxgt
Msg: The statement is executed successfully.
IoTDB> show child nodes root.gsxgt
show child nodes root.gsxgt
+-----------+
|child nodes|
+-----------+
+-----------+
Empty set.
It costs 0.005s
IoTDB> CREATE TIMESERIES root.gsxgt.d1 WITH DATATYPE=BOOLEAN, ENCODING=PLAIN
CREATE TIMESERIES root.gsxgt.d1 WITH DATATYPE=BOOLEAN, ENCODING=PLAIN
Msg: The statement is executed successfully.
IoTDB> show child nodes root.gsxgt
show child nodes root.gsxgt
+-----------+
|child nodes|
+-----------+
| d1|
+-----------+
Total line number = 1
It costs 0.009s
IoTDB> show child nodes root.gsxgt.d1
show child nodes root.gsxgt.d1
+-----------+
|child nodes|
+-----------+
+-----------+
Empty set.
It costs 0.004s
IoTDB> CREATE TIMESERIES root.gsxgt.d1.s1 WITH DATATYPE=BOOLEAN,
ENCODING=PLAIN
CREATE TIMESERIES root.gsxgt.d1.s1 WITH DATATYPE=BOOLEAN, ENCODING=PLAIN
Msg: The statement is executed successfully.
IoTDB> show child nodes root.gsxgt.d1
show child nodes root.gsxgt.d1
+-----------+
|child nodes|
+-----------+
| s1|
+-----------+
Total line number = 1
It costs 0.005s
  2、org.apache.iotdb.db.metadata.MTreeTest --> Add Child Node as
an empty scene
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