refactor: improve database initialization by centralizing db instance injection

- Move db configs to separate methods
- Remove db field defaults in storage classes
- Add _initialize_database_if_needed method
- Inject db instances during initialization
- Clean up storage implementation code

lightrag/kg/postgres_impl.py

@@ -177,7 +177,8 @@ class PostgreSQLDB:
 
 @dataclass
 class PGKVStorage(BaseKVStorage):
-    db: PostgreSQLDB = None
+    # db instance must be injected before use
+    # db: PostgreSQLDB
 
     def __post_init__(self):
         self._max_batch_size = self.global_config["embedding_batch_num"]
@@ -296,8 +297,9 @@ class PGKVStorage(BaseKVStorage):
 
 @dataclass
 class PGVectorStorage(BaseVectorStorage):
+    # db instance must be injected before use
+    # db: PostgreSQLDB
     cosine_better_than_threshold: float = float(os.getenv("COSINE_THRESHOLD", "0.2"))
-    db: PostgreSQLDB = None
 
     def __post_init__(self):
         self._max_batch_size = self.global_config["embedding_batch_num"]
@@ -418,10 +420,8 @@ class PGVectorStorage(BaseVectorStorage):
 class PGDocStatusStorage(DocStatusStorage):
     """PostgreSQL implementation of document status storage"""
 
-    db: PostgreSQLDB = None
-
-    def __post_init__(self):
-        pass
+    # db instance must be injected before use
+    db: PostgreSQLDB
 
     async def filter_keys(self, data: set[str]) -> set[str]:
         """Return keys that don't exist in storage"""
@@ -577,19 +577,15 @@ class PGGraphQueryException(Exception):
 
 @dataclass
 class PGGraphStorage(BaseGraphStorage):
-    db: PostgreSQLDB = None
+    # db instance must be injected before use
+    # db: PostgreSQLDB
 
     @staticmethod
     def load_nx_graph(file_name):
         print("no preloading of graph with AGE in production")
 
-    def __init__(self, namespace, global_config, embedding_func):
-        super().__init__(
-            namespace=namespace,
-            global_config=global_config,
-            embedding_func=embedding_func,
-        )
-        self.graph_name = os.environ["AGE_GRAPH_NAME"]
+    def __post_init__(self):
+        self.graph_name = os.environ.get("AGE_GRAPH_NAME", "lightrag")
         self._node_embed_algorithms = {
             "node2vec": self._node2vec_embed,
         }