topic: Move sqlalchemy methods into their own file.

Loading sqlalchemy can take a significant amount of time, so splitting
these into these own file can be a significant startup-time savings.

tools/linter_lib/custom_check.py

@@ -13,6 +13,7 @@ from zulint.custom_rules import Rule, RuleList
 FILES_WITH_LEGACY_SUBJECT = {
     # This basically requires a big DB migration:
     "zerver/lib/topic.py",
+    "zerver/lib/topic_sqlalchemy.py",
     # This is for backward compatibility.
     "zerver/tests/test_legacy_subject.py",
     # Other migration-related changes require extreme care.

zerver/lib/narrow.py

@@ -58,10 +58,9 @@ from zerver.lib.streams import (
     get_stream_by_narrow_operand_access_unchecked,
     get_web_public_streams_queryset,
 )
-from zerver.lib.topic import (
+from zerver.lib.topic import RESOLVED_TOPIC_PREFIX, get_topic_from_message_info
-    RESOLVED_TOPIC_PREFIX,
+from zerver.lib.topic_sqlalchemy import (
     get_resolved_topic_condition_sa,
-    get_topic_from_message_info,
     topic_column_sa,
     topic_match_sa,
 )

zerver/lib/topic.py

@@ -5,8 +5,6 @@ import orjson
 from django.db import connection
 from django.db.models import F, Func, JSONField, Q, QuerySet, Subquery, TextField, Value
 from django.db.models.functions import Cast
-from sqlalchemy.sql import ColumnElement, column, func, literal
-from sqlalchemy.types import Boolean, Text
 
 from zerver.lib.request import REQ
 from zerver.lib.types import EditHistoryEvent
@@ -72,22 +70,6 @@ DB_TOPIC_NAME = "subject"
 MESSAGE__TOPIC = "message__subject"
 
 
-def topic_match_sa(topic_name: str) -> ColumnElement[Boolean]:
-    # _sa is short for SQLAlchemy, which we use mostly for
-    # queries that search messages
-    topic_cond = func.upper(column("subject", Text)) == func.upper(literal(topic_name))
-    return topic_cond
-
-
-def get_resolved_topic_condition_sa() -> ColumnElement[Boolean]:
-    resolved_topic_cond = column("subject", Text).startswith(RESOLVED_TOPIC_PREFIX)
-    return resolved_topic_cond
-
-
-def topic_column_sa() -> ColumnElement[Text]:
-    return column("subject", Text)
-
-
 def filter_by_topic_name_via_message(
     query: QuerySet[UserMessage], topic_name: str
 ) -> QuerySet[UserMessage]:

zerver/lib/topic_sqlalchemy.py

@@ -0,0 +1,20 @@
+from sqlalchemy.sql import ColumnElement, column, func, literal
+from sqlalchemy.types import Boolean, Text
+
+from zerver.lib.topic import RESOLVED_TOPIC_PREFIX
+
+
+def topic_match_sa(topic_name: str) -> ColumnElement[Boolean]:
+    # _sa is short for SQLAlchemy, which we use mostly for
+    # queries that search messages
+    topic_cond = func.upper(column("subject", Text)) == func.upper(literal(topic_name))
+    return topic_cond
+
+
+def get_resolved_topic_condition_sa() -> ColumnElement[Boolean]:
+    resolved_topic_cond = column("subject", Text).startswith(RESOLVED_TOPIC_PREFIX)
+    return resolved_topic_cond
+
+
+def topic_column_sa() -> ColumnElement[Text]:
+    return column("subject", Text)

zerver/lib/user_topics.py

@@ -10,7 +10,7 @@ from sqlalchemy.sql import ClauseElement, and_, column, not_, or_
 from sqlalchemy.types import Integer
 
 from zerver.lib.timestamp import datetime_to_timestamp
-from zerver.lib.topic import topic_match_sa
+from zerver.lib.topic_sqlalchemy import topic_match_sa
 from zerver.lib.types import UserTopicDict
 from zerver.models import UserProfile, UserTopic
 from zerver.models.streams import get_stream

zerver/views/message_fetch.py

@@ -24,7 +24,8 @@ from zerver.lib.narrow import (
 from zerver.lib.request import REQ, RequestNotes, has_request_variables
 from zerver.lib.response import json_success
 from zerver.lib.sqlalchemy_utils import get_sqlalchemy_connection
-from zerver.lib.topic import DB_TOPIC_NAME, MATCH_TOPIC, topic_column_sa
+from zerver.lib.topic import DB_TOPIC_NAME, MATCH_TOPIC
+from zerver.lib.topic_sqlalchemy import topic_column_sa
 from zerver.lib.validator import check_bool, check_int, check_list, to_non_negative_int
 from zerver.models import UserMessage, UserProfile