fixed models.py to remove edges id

backend/app.py

 from flask import Flask, jsonify, request
-from sqlalchemy.orm import sessionmaker
+from sqlalchemy.orm import sessionmaker, scoped_session
 from sqlalchemy import create_engine
 from backend.models import Node, Edge
 from dotenv import load_dotenv
@@ -19,8 +19,10 @@ DATABASE_URL = os.getenv('DATABASE_URL')
 if not DATABASE_URL:
     raise ValueError("DATABASE_URL is not set in the environment variables")
 
+# Create engine and session factory
 engine = create_engine(DATABASE_URL)
-Session = sessionmaker(bind=engine)
+session_factory = sessionmaker(bind=engine)
+Session = scoped_session(session_factory)
 
 @app.route('/nodes', methods=['GET'])
 def get_nodes():
@@ -50,5 +52,10 @@ def get_edges():
     except Exception as e:
         return jsonify({'error': str(e)}), 500
 
+# Ensure scoped_session is removed after each request
+@app.teardown_appcontext
+def remove_session(exception=None):
+    Session.remove()
+
 if __name__ == '__main__':
     app.run(debug=True)

backend/models.py

-from sqlalchemy import Column, Integer, Float, String
+from sqlalchemy import Column, Integer, Float, String, PrimaryKeyConstraint
 from sqlalchemy.ext.declarative import declarative_base
 
 Base = declarative_base()
@@ -29,10 +29,10 @@ class Node(Base):
             'district': self.district
         }
 
-# Example for Edge model
+# Example for Edge model with composite primary key
 class Edge(Base):
     __tablename__ = 'edges'
-    id = Column(String, primary_key=True)
+    
     source = Column(String)
     target = Column(String)
     label = Column(String)
@@ -43,9 +43,12 @@ class Edge(Base):
     distance = Column(Float)
     edge_type = Column(String)
 
+    __table_args__ = (
+        PrimaryKeyConstraint('source', 'target'),
+    )
+
     def to_dict(self):
         return {
-            'id': self.id,
             'source': self.source,
             'target': self.target,
             'label': self.label,