models.py

from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.orm import relationship
from database import Base

class Enrollment(Base):
    __tablename__ = "enrollments"
    student_id = Column(Integer, ForeignKey("students.id"), primary_key=True)
    course_id = Column(Integer, ForeignKey("courses.id"), primary_key=True)
    grade = Column(String, nullable=True)

    student = relationship("Student", back_populates="enrollments")
    course = relationship("Course", back_populates="enrollments")

class Department(Base):
    __tablename__ = "departments"
    id = Column(Integer, primary_key=True, index=True)
    name = Column(String, unique=True, nullable=False, index=True)

    courses = relationship("Course", back_populates="department")

class Teacher(Base):
    __tablename__ = "teachers"

    id = Column(Integer, primary_key=True, index=True)
    name = Column(String, nullable=False, index=True)

    courses = relationship("Course", back_populates="teacher")

class Course(Base):
    __tablename__ = "courses"

    id = Column(Integer, primary_key=True, index=True)
    title = Column(String, nullable=False, index=True)

    department_id = Column(Integer, ForeignKey("departments.id"), nullable=False)
    teacher_id = Column(Integer, ForeignKey("teachers.id"), nullable=True)

    department = relationship("Department", back_populates="courses")
    teacher = relationship("Teacher", back_populates="courses")

    enrollments = relationship("Enrollment", back_populates="course", cascade="all, delete-orphan")

class Student(Base):
    __tablename__ = "students"

    id = Column(Integer, primary_key=True, index=True)
    name = Column(String, nullable=False, index=True)

    enrollments = relationship("Enrollment", back_populates="student", cascade="all, delete-orphan")