add one to many relationships and various updates surrounding this

class_client.py

@@ -1,7 +1,9 @@
 # Lucas Mathews - Fontys Student ID: 5023572
 # Banking System Client Class
 
-from sqlalchemy import Column, String, Boolean
+from sqlalchemy import Column, String, Boolean, ForeignKey
+from sqlalchemy.orm import relationship
+
 
 from class_base import Base
 
@@ -18,7 +20,7 @@ class Client(Base):
     notes = Column("notes", String)
     enabled = Column("enabled", Boolean)
     administrator = Column("administrator", Boolean)
-    accounts = Column("accounts", String)
+    accounts = relationship("Account", backref="client")
 
     def __init__(self, client_id, name, birthdate, opening_timestamp, address, phone_number, email, hash, notes, enabled, administrator, accounts):
         self.client_id = client_id
@@ -32,7 +34,7 @@ class Client(Base):
         self.notes = notes
         self.enabled = enabled
         self.administrator = administrator
-        self.accounts = accounts
+        self.accounts = accounts if accounts is not None else []
     
     def __repr__(self):
         return f"Client ID: {self.client_id}, Name: {self.name}, Birthdate: {self.birthdate}, Address: {self.address}, Phone Number: {self.phone_number}, Email: {self.email}, Enabled: {self.enabled}, Accounts: {self.accounts}"