add get_db method

backend/forum.py

@@ -1,6 +1,6 @@
 from fastapi import FastAPI
 import models
-from database import engine
+from database import engine, SessionLocal
 from pydantic import BaseModel
 
 app = FastAPI()
@@ -8,6 +8,14 @@ app = FastAPI()
 models.Base.metadata.create_all(bind=engine)
 
 
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()
+
+
 class Post:
     """Post is a single forum post or reply"""
     id: int