Add lazy evaluation of server_version_info

Author: mdesmet

tests/integration/test_sqlalchemy_integration.py

@@ -15,6 +15,7 @@
 import sqlalchemy as sqla
 from sqlalchemy.sql import and_, not_, or_
 
+from tests.integration.conftest import trino_version
 from tests.unit.conftest import sqlalchemy_version
 from trino.sqlalchemy.datatype import JSON
 
@@ -497,3 +498,24 @@ def test_get_view_names_raises(trino_connection):
 
     with pytest.raises(sqla.exc.NoSuchTableError):
         sqla.inspect(engine).get_view_names(None)
+
+
+@pytest.mark.parametrize('trino_connection', ['system'], indirect=True)
+@pytest.mark.skipif(trino_version() == '351', reason="version() not supported in older Trino versions")
+def test_version_is_lazy(trino_connection):
+    _, conn = trino_connection
+    result = conn.execute(sqla.text("SELECT 1"))
+    result.fetchall()
+    num_queries = _num_queries_containing_string(conn, "SELECT version()")
+    assert num_queries == 0
+    version_info = conn.dialect.server_version_info
+    assert isinstance(version_info, tuple)
+    num_queries = _num_queries_containing_string(conn, "SELECT version()")
+    assert num_queries == 1
+
+
+def _num_queries_containing_string(connection, query_string):
+    statement = sqla.text("select query from system.runtime.queries order by query_id desc offset 1 limit 1")
+    result = connection.execute(statement)
+    rows = result.fetchall()
+    return len(list(filter(lambda rec: query_string in rec[0], rows)))

trino/sqlalchemy/dialect.py

@@ -336,15 +336,20 @@ def has_sequence(self, connection: Connection, sequence_name: str, schema: str =
         """Trino has no support for sequence. Returns False indicate that given sequence does not exists."""
         return False
 
-    def _get_server_version_info(self, connection: Connection) -> Any:
-        query = "SELECT version()"
-        try:
-            res = connection.execute(sql.text(query))
-            version = res.scalar()
-            return tuple([version])
-        except exc.ProgrammingError as e:
-            logger.debug(f"Failed to get server version: {e.orig.message}")
-            return None
+    @classmethod
+    def _get_server_version_info(cls, connection: Connection) -> Any:
+        def get_server_version_info(_):
+            query = "SELECT version()"
+            try:
+                res = connection.execute(sql.text(query))
+                version = res.scalar()
+                return tuple([version])
+            except exc.ProgrammingError as e:
+                logger.debug(f"Failed to get server version: {e.orig.message}")
+                return None
+
+        # Make server_version_info lazy in order to only make HTTP calls if user explicitly requests it.
+        cls.server_version_info = property(get_server_version_info, lambda instance, value: None)
 
     def _raw_connection(self, connection: Union[Engine, Connection]) -> trino_dbapi.Connection:
         if isinstance(connection, Engine):