Account for DB aliases when recording transaction state

The logic in SQLPanel.generate_stats() did not properly account for the
DB alias when marking transactions as ended.  It would always mark the
previous query as ending the transaction even if the previous query was
from a different DB alias.

Update the code to track the last query by alias so that the correct
query can be marked as ending the transaction.

Author: living180

debug_toolbar/panels/sql/panel.py

@@ -178,23 +178,25 @@ def duplicate_key(query):
                     rgb[nn] = nc
                 db["rgb_color"] = rgb
 
-            trans_ids = {}
-            trans_id = None
-            i = 0
+            # the last query recorded for each DB alias
+            last_by_alias = {}
             for alias, query in self._queries:
                 query_similar[alias][similar_key(query)] += 1
                 query_duplicates[alias][duplicate_key(query)] += 1
 
                 trans_id = query.get("trans_id")
-                last_trans_id = trans_ids.get(alias)
-
-                if trans_id != last_trans_id:
-                    if last_trans_id:
-                        self._queries[(i - 1)][1]["ends_trans"] = True
-                    trans_ids[alias] = trans_id
-                    if trans_id:
+                prev_query = last_by_alias.get(alias, {})
+                prev_trans_id = prev_query.get("trans_id")
+
+                # If two consecutive queries for a given DB alias have different
+                # transaction ID values, a transaction started, finished, or both, so
+                # annotate the queries as appropriate.
+                if trans_id != prev_trans_id:
+                    if prev_trans_id is not None:
+                        prev_query["ends_trans"] = True
+                    if trans_id is not None:
                         query["starts_trans"] = True
-                if trans_id:
+                if trans_id is not None:
                     query["in_trans"] = True
 
                 query["alias"] = alias
@@ -222,12 +224,16 @@ def duplicate_key(query):
                 query["end_offset"] = query["width_ratio"] + query["start_offset"]
                 width_ratio_tally += query["width_ratio"]
                 query["stacktrace"] = render_stacktrace(query["stacktrace"])
-                i += 1
 
                 query["trace_color"] = trace_colors[query["stacktrace"]]
 
-            if trans_id:
-                self._queries[(i - 1)][1]["ends_trans"] = True
+                last_by_alias[alias] = query
+
+            # Close out any transactions that were in progress, since there is no
+            # explicit way to know when a transaction finishes.
+            for final_query in last_by_alias.values():
+                if final_query.get("trans_id") is not None:
+                    final_query["ends_trans"] = True
 
         # Queries are similar / duplicates only if there's as least 2 of them.
         # Also, to hide queries, we need to give all the duplicate groups an id