Fix cursor.py failing in SELECT * queries (#16)

There was a recent change in Rockset that removes the `column_fields`
field rather than keeping it an empty array in cases where columns are
not specified in the query (i.e. `SELECT *`), which causes an exception
to be raised when the field is accessed.

This change should resolve the crash and return the library to its
previous behavior.

src/rockset_sqlalchemy/connection.py

@@ -3,13 +3,11 @@
 from .cursor import Cursor
 from .exceptions import ProgrammingError
 
+
 class Connection(object):
     def __init__(self, api_server, api_key, virtual_instance=None, debug_sql=False):
         self._closed = False
-        self._client = RocksetClient(
-            host=api_server, 
-            api_key=api_key
-        )
+        self._client = RocksetClient(host=api_server, api_key=api_key)
         self.vi = virtual_instance
         self.debug_sql = debug_sql
         # Used for testing connectivity to Rockset.

src/rockset_sqlalchemy/cursor.py

@@ -43,18 +43,23 @@ def execute_query(client, query, vi=None, query_params={}):
             query=query,
             parameters=[
                 rockset.models.QueryParameter(
-                    name=param, value=str(val), type=Cursor.__convert_to_rockset_type(val)
+                    name=param,
+                    value=str(val),
+                    type=Cursor.__convert_to_rockset_type(val),
                 )
                 for param, val in query_params.items()
-            ]
+            ],
         )
         try:
-            return client.VirtualInstances.query_virtual_instance(
-                virtual_instance_id=vi,
-                sql=request
-            ) if vi else client.Queries.query(sql=request)
+            return (
+                client.VirtualInstances.query_virtual_instance(
+                    virtual_instance_id=vi, sql=request
+                )
+                if vi
+                else client.Queries.query(sql=request)
+            )
         except rockset.exceptions.RocksetException as e:
-            raise Error.map_rockset_exception(e)  
+            raise Error.map_rockset_exception(e)
 
     def execute(self, sql, parameters=None):
         self.__check_cursor_opened()
@@ -68,7 +73,7 @@ def execute(self, sql, parameters=None):
                 else:
                     new_params[k] = v
         parameters = new_params
-        
+
         if self._connection.debug_sql:
             print("+++++++++++++++++++++++++++++")
             print(f"Query:\n{sql}")
@@ -83,10 +88,7 @@ def execute(self, sql, parameters=None):
             )
 
         self._response = Cursor.execute_query(
-            self._connection._client,
-            sql, 
-            self._connection.vi,
-            query_params=parameters
+            self._connection._client, sql, self._connection.vi, query_params=parameters
         )
         self._response_iter = iter(self._response.results)
 
@@ -108,8 +110,9 @@ def fetchone(self):
             return None
 
         result = []
-
-        for field in self._response_to_column_fields(self._response.column_fields):           
+
+        column_fields = getattr(self._response, "column_fields", None)
+        for field in self._response_to_column_fields(column_fields):
             name = field["name"]
             if name in next_doc:
                 result.append(next_doc[name])
@@ -126,7 +129,7 @@ def _response_to_column_fields(self, column_fields):
 
         schema = rockset.Document()
         if self._response.results and len(self._response.results) > 0:
-            # we only look at the first document because 
+            # we only look at the first document because
             # is sqlalchemy is typically used for relational
             # tables with no sparse fields
             schema.update(self._response.results[0])
@@ -152,7 +155,6 @@ def fetchmany(self, size=None):
                 break
             docs.append(doc)
         return docs
-
 
     @property
     def description(self):

src/rockset_sqlalchemy/exceptions.py

@@ -1,31 +1,27 @@
 import rockset
 from json import loads
 
+
 class Error(rockset.exceptions.RocksetException):
     @classmethod
     def map_rockset_exception(cls, exc):
         err_body = loads(exc.body)
-        args = [
-            err_body["message"],
-            exc.status,
-            err_body["type"]
-        ]
+        args = [err_body["message"], exc.status, err_body["type"]]
         exc_type = type(exc)
         if (
-            exc_type == rockset.exceptions.ApiTypeError or
-            exc_type == rockset.exceptions.ApiValueError or
-            exc_type == rockset.exceptions.ApiAttributeError or
-            exc_type == rockset.exceptions.ApiKeyError or 
-            exc_type == rockset.exceptions.NotFoundException or
-            exc_type == rockset.exceptions.InputException or  
-            exc_type == rockset.exceptions.InitializationException or
-            exc_type == rockset.exceptions.BadRequestException
-
+            exc_type == rockset.exceptions.ApiTypeError
+            or exc_type == rockset.exceptions.ApiValueError
+            or exc_type == rockset.exceptions.ApiAttributeError
+            or exc_type == rockset.exceptions.ApiKeyError
+            or exc_type == rockset.exceptions.NotFoundException
+            or exc_type == rockset.exceptions.InputException
+            or exc_type == rockset.exceptions.InitializationException
+            or exc_type == rockset.exceptions.BadRequestException
         ):
             ret = ProgrammingError(*args)
         elif (
-            exc_type == rockset.exceptions.UnauthorizedException or 
-            exc_type == rockset.exceptions.ForbiddenException
+            exc_type == rockset.exceptions.UnauthorizedException
+            or exc_type == rockset.exceptions.ForbiddenException
         ):
             ret = OperationalError(*args)
         elif exc_type == rockset.exceptions.ServiceException:

src/rockset_sqlalchemy/sqlalchemy/dialect.py

@@ -43,12 +43,11 @@ class RocksetDialect(default.DefaultDialect):
 
     @classmethod
     def dbapi(cls):
-        """Retained for backward compatibility with SQLAlchemy 1.x.
-        """
+        """Retained for backward compatibility with SQLAlchemy 1.x."""
         import rockset_sqlalchemy
 
         return rockset_sqlalchemy
-    
+
     @classmethod
     def import_dbapi(cls):
         return RocksetDialect.dbapi()
@@ -57,20 +56,27 @@ def create_connect_args(self, url):
         kwargs = {
             "api_server": "https://{}".format(url.host),
             "api_key": url.password or url.username,
-            "virtual_instance": url.database
+            "virtual_instance": url.database,
         }
         return ([], kwargs)
 
     @reflection.cache
     def get_schema_names(self, connection, **kw):
-        return [w["name"] for w in connection.connect().connection._client.Workspaces.list()["data"]]
+        return [
+            w["name"]
+            for w in connection.connect().connection._client.Workspaces.list()["data"]
+        ]
 
     @reflection.cache
     def get_table_names(self, connection, schema=None, **kw):
-        tables = (connection.connect().connection._client.Collections.list()
-                if schema is None else 
-                connection.connect().connection._client.Collections.workspace_collections(workspace=schema))['data']
-
+        tables = (
+            connection.connect().connection._client.Collections.list()
+            if schema is None
+            else connection.connect().connection._client.Collections.workspace_collections(
+                workspace=schema
+            )
+        )["data"]
+
         return [w["name"] for w in tables]
 
     def _get_table_columns(self, connection, table_name, schema):
@@ -132,7 +138,7 @@ def get_pk_constraint(self, connection, table_name, schema=None, **kw):
     @reflection.cache
     def get_indexes(self, connection, table_name, schema=None, **kw):
         return []
-    
+
     def has_table(self, connection, table_name, schema=None):
         try:
             self._get_table_columns(connection, table_name, schema)