feat: Add singleton way of working to graph databases

Added signleton type of functioning to graph databases

Feature

cognee/infrastructure/databases/graph/get_graph_engine.py

@@ -1,44 +1,58 @@
 """Factory function to get the appropriate graph client based on the graph type."""
+from functools import lru_cache
 
 from .config import get_graph_config
 from .graph_db_interface import GraphDBInterface
 
 
-async def get_graph_engine() -> GraphDBInterface :
+async def get_graph_engine() -> GraphDBInterface:
     """Factory function to get the appropriate graph client based on the graph type."""
+    graph_client = create_graph_engine()
+
+    # Async functions can't be cached. After creating and caching the graph engine
+    # handle all necessary async operations for different graph types bellow.
+    config = get_graph_config()
+
+    # Handle loading of graph for NetworkX
+    if config.graph_database_provider.lower() == "networkx" and graph_client.graph is None:
+        await graph_client.load_graph_from_file()
+
+    return graph_client
+
+
+@lru_cache
+def create_graph_engine() -> GraphDBInterface:
+    """Factory function to create the appropriate graph client based on the graph type."""
     config = get_graph_config()
 
     if config.graph_database_provider == "neo4j":
         if not (config.graph_database_url and config.graph_database_username and config.graph_database_password):
             raise EnvironmentError("Missing required Neo4j credentials.")
-      
+
         from .neo4j_driver.adapter import Neo4jAdapter
 
         return Neo4jAdapter(
-            graph_database_url = config.graph_database_url,
-            graph_database_username = config.graph_database_username,
-            graph_database_password = config.graph_database_password
+            graph_database_url=config.graph_database_url,
+            graph_database_username=config.graph_database_username,
+            graph_database_password=config.graph_database_password
         )
 
     elif config.graph_database_provider == "falkordb":
         if not (config.graph_database_url and config.graph_database_username and config.graph_database_password):
             raise EnvironmentError("Missing required FalkorDB credentials.")
-      
+
         from cognee.infrastructure.databases.vector.embeddings import get_embedding_engine
         from cognee.infrastructure.databases.hybrid.falkordb.FalkorDBAdapter import FalkorDBAdapter
 
         embedding_engine = get_embedding_engine()
 
         return FalkorDBAdapter(
-            database_url = config.graph_database_url,
-            database_port = config.graph_database_port,
-            embedding_engine = embedding_engine,
+            database_url=config.graph_database_url,
+            database_port=config.graph_database_port,
+            embedding_engine=embedding_engine,
         )
 
     from .networkx.adapter import NetworkXAdapter
-    graph_client = NetworkXAdapter(filename = config.graph_file_path)
-
-    if graph_client.graph is None:
-        await graph_client.load_graph_from_file()
+    graph_client = NetworkXAdapter(filename=config.graph_file_path)
 
     return graph_client