fix(orm): correct asymmetric relationships, add missing back_populates, and remove invalid model refs

src/app/models/ticket.py

@@ -114,6 +114,8 @@ class Ticket(BaseModel):
     project = relationship("Project", back_populates="tickets")
     project_region = relationship("ProjectRegion", foreign_keys=[project_region_id])
     contractor_invoice = relationship("ContractorInvoice", foreign_keys=[contractor_invoice_id], backref="tickets")
+    sales_order = relationship("SalesOrder", back_populates="ticket", uselist=False, foreign_keys="[Ticket.source_id]", 
+                               primaryjoin="and_(Ticket.source_id==SalesOrder.id, Ticket.source_type=='sales_order')")
     assignments = relationship("TicketAssignment", back_populates="ticket", cascade="all, delete-orphan", lazy="select")
     expenses = relationship("TicketExpense", back_populates="ticket", cascade="all, delete-orphan", lazy="select")
     comments = relationship("TicketComment", back_populates="ticket", cascade="all, delete-orphan", lazy="select")

src/app/models/ticket_assignment.py

@@ -82,7 +82,7 @@ class TicketAssignment(BaseModel):
     user = relationship("User", foreign_keys=[user_id], lazy="select")
     assigned_by = relationship("User", foreign_keys=[assigned_by_user_id], lazy="select")
     expenses = relationship("TicketExpense", back_populates="assignment", cascade="all, delete-orphan")
-    status_changes = relationship("TicketStatusHistory", back_populates="assignment", cascade="all, delete-orphan")
+    # status_changes = relationship("TicketStatusHistory", back_populates="assignment", cascade="all, delete-orphan")  # Model doesn't exist yet
 
     def __repr__(self):
         return f"<TicketAssignment(id={self.id}, ticket_id={self.ticket_id}, user_id={self.user_id}, action={self.action}, status={self.status})>"

src/app/models/ticket_expense.py

@@ -123,7 +123,7 @@ class TicketExpense(Base):
     deleted_at = Column(TIMESTAMP(timezone=True), nullable=True)
     
     # Relationships
-    ticket_assignment = relationship("TicketAssignment", back_populates="expenses")
+    assignment = relationship("TicketAssignment", back_populates="expenses")  # Changed from ticket_assignment to assignment
     ticket = relationship("Ticket", back_populates="expenses")
     incurred_by_user = relationship("User", foreign_keys=[incurred_by_user_id])
     approved_by_user = relationship("User", foreign_keys=[approved_by_user_id])

src/app/models/user.py

@@ -4,6 +4,7 @@ Matches schema.sql exactly - field service management platform
 """
 from sqlalchemy import Column, String, Boolean, Text, DateTime, Float
 from sqlalchemy.dialects.postgresql import UUID, JSONB
+from sqlalchemy.orm import relationship
 from app.models.base import BaseModel
 
 
@@ -89,6 +90,13 @@ class User(BaseModel):
     # Additional Metadata
     additional_metadata = Column(JSONB, default={})
     
+    # Relationships - Using backref for most, explicit back_populates where needed
+    # Note: Most relationships use backref in the referring model (one-way is sufficient)
+    # Only add back_populates when bidirectional traversal is explicitly needed
+    
+    # Sales orders where this user is the agent (explicit back_populates)
+    sales_orders_as_agent = relationship("SalesOrder", foreign_keys="[SalesOrder.sales_agent_id]", back_populates="sales_agent", lazy="dynamic")
+    
     def __repr__(self):
         return f"<User(email='{self.email}', name='{self.name}', role='{self.role}')>"