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perf: fix N+1 tag queries in activities and dashboard APIs #31

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perf: fix N+1 tag queries in activities and dashboard APIs #31

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f869b62
perf: fix N+1 tag queries in activities and dashboard APIs
Mar 29, 2026
8bdec94
Merge branch 'main' into fix/n-plus-1-tag-queries
ankushchk Mar 29, 2026
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51 changes: 23 additions & 28 deletions src/worker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -747,9 +747,13 @@ async def api_list_activities(req, env):
"a.created_at,u.name AS host_name_enc,"
"(SELECT COUNT(*) FROM enrollments WHERE activity_id=a.id AND status='active')"
" AS participant_count,"
"(SELECT COUNT(*) FROM sessions WHERE activity_id=a.id) AS session_count"
"(SELECT COUNT(*) FROM sessions WHERE activity_id=a.id) AS session_count,"
"GROUP_CONCAT(t.name) AS tag_names"
" FROM activities a JOIN users u ON a.host_id=u.id"
" LEFT JOIN activity_tags at2 ON at2.activity_id=a.id"
" LEFT JOIN tags t ON t.id=at2.tag_id"
)
group_order = " GROUP BY a.id ORDER BY a.created_at DESC"

if tag:
tag_row = await env.DB.prepare(
Expand All @@ -758,25 +762,23 @@ async def api_list_activities(req, env):
if not tag_row:
return json_resp({"activities": []})
res = await env.DB.prepare(
base_q
+ " JOIN activity_tags at2 ON at2.activity_id=a.id"
" WHERE at2.tag_id=? ORDER BY a.created_at DESC"
base_q + " WHERE at2.tag_id=?" + group_order
).bind(tag_row.id).all()
elif atype and fmt:
res = await env.DB.prepare(
base_q + " WHERE a.type=? AND a.format=? ORDER BY a.created_at DESC"
base_q + " WHERE a.type=? AND a.format=?" + group_order
).bind(atype, fmt).all()
elif atype:
res = await env.DB.prepare(
base_q + " WHERE a.type=? ORDER BY a.created_at DESC"
base_q + " WHERE a.type=?" + group_order
).bind(atype).all()
elif fmt:
res = await env.DB.prepare(
base_q + " WHERE a.format=? ORDER BY a.created_at DESC"
base_q + " WHERE a.format=?" + group_order
).bind(fmt).all()
else:
res = await env.DB.prepare(
base_q + " ORDER BY a.created_at DESC"
base_q + group_order
).all()

activities = []
Expand All @@ -789,12 +791,6 @@ async def api_list_activities(req, env):
):
continue

t_res = await env.DB.prepare(
"SELECT t.name FROM tags t"
" JOIN activity_tags at2 ON at2.tag_id=t.id"
" WHERE at2.activity_id=?"
).bind(row.id).all()

activities.append({
"id": row.id,
"title": row.title,
Expand All @@ -805,7 +801,7 @@ async def api_list_activities(req, env):
"host_name": host_name,
"participant_count": row.participant_count,
"session_count": row.session_count,
"tags": [t.name for t in (t_res.results or [])],
"tags": row.tag_names.split(",") if row.tag_names else [],
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"created_at": row.created_at,
})

Expand Down Expand Up @@ -1000,16 +996,16 @@ async def api_dashboard(req, env):
"SELECT a.id,a.title,a.type,a.format,a.schedule_type,a.created_at,"
"(SELECT COUNT(*) FROM enrollments WHERE activity_id=a.id AND status='active')"
" AS participant_count,"
"(SELECT COUNT(*) FROM sessions WHERE activity_id=a.id) AS session_count"
" FROM activities a WHERE a.host_id=? ORDER BY a.created_at DESC"
"(SELECT COUNT(*) FROM sessions WHERE activity_id=a.id) AS session_count,"
"GROUP_CONCAT(t.name) AS tag_names"
" FROM activities a"
" LEFT JOIN activity_tags at2 ON at2.activity_id=a.id"
" LEFT JOIN tags t ON t.id=at2.tag_id"
" WHERE a.host_id=? GROUP BY a.id ORDER BY a.created_at DESC"
).bind(user["id"]).all()

hosted = []
for r in res.results or []:
t_res = await env.DB.prepare(
"SELECT t.name FROM tags t JOIN activity_tags at2 ON at2.tag_id=t.id"
" WHERE at2.activity_id=?"
).bind(r.id).all()
hosted.append({
"id": r.id,
"title": r.title,
Expand All @@ -1018,26 +1014,25 @@ async def api_dashboard(req, env):
"schedule_type": r.schedule_type,
"participant_count": r.participant_count,
"session_count": r.session_count,
"tags": [t.name for t in (t_res.results or [])],
"tags": r.tag_names.split(",") if r.tag_names else [],
"created_at": r.created_at,
})

res2 = await env.DB.prepare(
"SELECT a.id,a.title,a.type,a.format,a.schedule_type,"
"e.role AS enr_role,e.status AS enr_status,e.created_at AS joined_at,"
"u.name AS host_name_enc"
"u.name AS host_name_enc,"
"GROUP_CONCAT(t.name) AS tag_names"
" FROM enrollments e"
" JOIN activities a ON e.activity_id=a.id"
" JOIN users u ON a.host_id=u.id"
" WHERE e.user_id=? ORDER BY e.created_at DESC"
" LEFT JOIN activity_tags at2 ON at2.activity_id=a.id"
" LEFT JOIN tags t ON t.id=at2.tag_id"
" WHERE e.user_id=? GROUP BY a.id ORDER BY e.created_at DESC"
).bind(user["id"]).all()

joined = []
for r in res2.results or []:
t_res = await env.DB.prepare(
"SELECT t.name FROM tags t JOIN activity_tags at2 ON at2.tag_id=t.id"
" WHERE at2.activity_id=?"
).bind(r.id).all()
joined.append({
"id": r.id,
"title": r.title,
Expand Down