Introduce exec_env.py to maintain global state + minor bug fix

1. The global database_instances is moved to exec_env.py to avoid
   circular imports.

2. SpannerFiledInfo.typename populated with the correct name now

Author: Sailesh Mukil Gangatharan

spanner_graphs/database.py

@@ -72,27 +72,9 @@ class SpannerFieldInfo:
 
 def get_as_field_info_list(fields: List[StructType.Field]) -> List[SpannerFieldInfo]:
   """Converts a list of StructType.Field to a list of SpannerFieldInfo."""
-  return [SpannerFieldInfo(name=field.name, typename=field.type_.code.name) for field in fields]
+  return [SpannerFieldInfo(name=field.name, typename=TypeCode(field.type_.code).name) for field in fields]
 
 
-# Global dict of database instances created in a single session
-database_instances: dict[str, SpannerDatabase | MockSpannerDatabase] = {}
-
-def get_database_instance(project: str, instance: str, database: str, mock = False) -> SpannerDatabase:
-    if mock:
-        return MockSpannerDatabase()
-
-    key = f"{project}_{instance}_{database}"
-    db = database_instances.get(key)
-
-    # Currently, we only create and return CloudSpannerDatabase instances. In the future, different
-    # implementations could be introduced.
-    if not db:
-        db = CloudSpannerDatabase(project, instance, database)
-        database_instances[key] = db
-
-    return db
-
 class MockSpannerResult:
 
     def __init__(self, file_path: str):

spanner_graphs/exec_env.py

@@ -0,0 +1,41 @@
+
+# Copyright 2024 Google LLC
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     https://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+This module maintains state for the execution environment of a session
+"""
+from typing import Dict, Union
+
+from spanner_graphs.database import SpannerDatabase, MockSpannerDatabase
+from spanner_graphs.cloud_database import CloudSpannerDatabase
+
+# Global dict of database instances created in a single session
+database_instances: Dict[str, Union[SpannerDatabase, MockSpannerDatabase]] = {}
+
+def get_database_instance(project: str, instance: str, database: str, mock = False):
+    if mock:
+        return MockSpannerDatabase()
+
+    key = f"{project}_{instance}_{database}"
+    db = database_instances.get(key)
+
+    # Currently, we only create and return CloudSpannerDatabase instances. In the future, different
+    # implementations could be introduced.
+    if not db:
+        db = CloudSpannerDatabase(project, instance, database)
+        database_instances[key] = db
+
+    return db
+

spanner_graphs/graph_server.py

@@ -25,7 +25,7 @@
 from google.cloud.spanner_v1 import TypeCode
 
 from spanner_graphs.conversion import get_nodes_edges
-from spanner_graphs.database import get_database_instance
+from spanner_graphs.exec_env import get_database_instance
 
 
 # Mapping of string types from frontend to Spanner TypeCode enum values

spanner_graphs/magics.py

@@ -33,7 +33,7 @@
 from ipywidgets import interact
 from jinja2 import Template
 
-from spanner_graphs.database import get_database_instance
+from spanner_graphs.exec_env import get_database_instance
 from spanner_graphs.graph_server import (
     GraphServer, execute_query, execute_node_expansion,
     validate_node_expansion_request