Mitigate proliferation of idle connections: SqlAlchemy Con --> Engine

backend/db/utils.py

@@ -206,6 +206,41 @@ def refresh_derived_tables(
             break
 
 
+ENGINES = {
+    # 'n3c': get_engine(),
+    # 'public': get_engine(schema='public')
+}
+
+
+def get_engine(isolation_level='AUTOCOMMIT', schema: str = SCHEMA, local=False):
+    """Connect to db
+    :param local: If True, connection is on local instead of production database."""
+    engine = ENGINES.get(schema, '') or create_engine(get_pg_connect_url(local), isolation_level=isolation_level)
+    if schema not in ENGINES:
+        ENGINES[schema] = engine
+
+    # noinspection PyUnusedLocal
+    @event.listens_for(engine, "connect", insert=True)
+    def set_search_path(dbapi_connection, connection_record):
+        """This does "set search_path to n3c;" when you connect.
+        https://docs.sqlalchemy.org/en/14/dialects/postgresql.html#setting-alternate-search-paths-on-connect
+        :param connection_record: Part of the example but we're not using yet.
+
+        Ideally, we'd want to be able to call this whenever we want. But cannot be called outside of context of
+        initializing a connection.
+        """
+        if not schema:
+            return
+        existing_autocommit = dbapi_connection.autocommit
+        dbapi_connection.autocommit = True
+        cursor = dbapi_connection.cursor()
+        cursor.execute(f"SET SESSION search_path='{schema}'")
+        cursor.close()
+        dbapi_connection.autocommit = existing_autocommit
+
+    return engine
+
+
 # todo: make 'isolation_level' the final param, since we never override it. this would it so we dont' have to pass the
 #  other params as named params.
 def get_db_connection(isolation_level='AUTOCOMMIT', schema: str = SCHEMA, local=False) -> Connection:

backend/routes/db.py

@@ -17,7 +17,8 @@
 from backend.api_logger import Api_logger, get_ip_from_request
 from backend.db.refresh import refresh_db
 from backend.db.queries import get_concepts
-from backend.db.utils import get_db_connection, sql_query, SCHEMA, sql_query_single_col, sql_in, sql_in_safe, run_sql
+from backend.db.utils import get_db_connection, get_engine, sql_query, SCHEMA, sql_query_single_col, sql_in, \
+    sql_in_safe, run_sql
 from backend.utils import return_err_with_trace, commify
 from enclave_wrangler.config import RESEARCHER_COLS
 from enclave_wrangler.models import convert_rows
@@ -597,8 +598,14 @@ def n3c_comparison_rpt():
     display comparison data compiled in generate_n3c_comparison_rpt()
         and get_comparison_rpt()
     """
-    with get_db_connection() as con:
+    engine = get_engine(schema='public')
+    with engine.connect() as con:
+    # with get_db_connection(schema='public') as con:
         rpt = sql_query_single_col(con, "SELECT rpt FROM public.codeset_comparison WHERE rpt IS NOT NULL")
+        print()
+    # con.close()
+    engine.dispose()
+    print()
     return rpt
 
 
@@ -609,7 +616,7 @@ def single_n3c_comparison_rpt(pair: str):
         and get_comparison_rpt()
     """
     orig_codeset_id, new_codeset_id = pair.split('-')
-    with get_db_connection() as con:
+    with get_db_connection(schema='public') as con:
         rpt = sql_query_single_col(
             con,
             "SELECT rpt FROM public.codeset_comparison WHERE orig_codeset_id || '-' || new_codeset_id = :pair",