app/models.py

from sqlalchemy import Column, ForeignKey, Integer, String, DateTime
from sqlalchemy.orm import relationship

from datetime import datetime

from database import Base

class User(Base):

    # 	This defines the name of the table in the database. 
    # Here, the class User is mapped to a table called users.
    __tablename__ = "users"
    __table_args__ = {'extend_existing': True}  

    # This line defines a column called id in the users table.
    # Integer: The data type of this column is an integer.
    # primary_key=True: This makes the id column the primary key 
    # for the users table, meaning each row will have a unique id.
    # index=True: This creates an index on the id column, making 
    # lookups by id faster.
    id = Column(Integer, primary_key=True, index=True)

    # This line defines a column called username.
    username = Column(String, unique=True, index=True)

    # This establishes a relationship between the User model 
    # and a related model called Message.
    # relationship("Message"): This creates a one-to-many relationship between User and Message. 
    # It indicates that each user can have many associated messages 
    # (the relationship is “one user to many messages”). 
    # back_populates="user": This specifies that the relationship is bidirectional, 
    # meaning the Message model will also have a corresponding relationship with User. 
    # The back_populates="user" part tells SQLAlchemy to link the relationship on the 
    # Message side back to the user field, creating a mutual relationship.
    messages = relationship("Message", back_populates="user")


# TODO: Implement the Message SQLAlchemy model. Message should have a primary key, 
# a message attribute to store the content of messages, a type, AI or Human, 
# depending on if it is a user question or an AI response, a timestamp to 
# order by time and a user attribute to get the user instance associated 
# with the message. We also need a user_id that will use the User.id 
# attribute as a foreign key.

class Message(Base):
    __tablename__ = "messages"
    __table_args__ = {'extend_existing': True} 

    id = id = Column(Integer, primary_key=True, index=True)
    message = Column(String, nullable=False)
    type = Column(String(50), nullable=False)
    timestamp = Column(DateTime, default=datetime.utcnow, nullable=False)
    user_id = Column(Integer, ForeignKey("users.id"), nullable=False)

    user = relationship("User", back_populates="messages")