sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) UNIQUE constraint failed - sql

Question

I am trying to create table for some courses, wհօse last column is another table and presents the lecturers names.
class Teachers(Base):
__tablename__ = 'teacher'
full_name = Column(String, unique=False, primary_key=True)
company = Column(String, unique = False)
class Course(Base):
__tablename__ = 'course'
course_name = Column(String, nullable=False)
course_id = Column(String,primary_key=True)
level = Column(String,unique=False)
teachers = Teachers
But I found following issue when the name of one lecturer is repeated in different courses:
sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) UNIQUE constraint failed: teacher.full_name
How can I solve this problem?

Answer 1

Your teachers column is not a column. Instead you are adding a whole table as an attribute.
What you should do, is defining a column in Course that contains the primary key of the Teacher (assuming there is only one teacher per course) and mark it as a ForeignKey. You can than also add a relationship for easier work.
from pathlib import Path
import sqlalchemy.orm
from sqlalchemy import Column, String, ForeignKey, create_engine
from sqlalchemy.orm import declarative_base, relationship
Base = declarative_base()
class Teacher(Base):
__tablename__ = "teachers"
full_name = Column(String, unique=False, primary_key=True)
company = Column(String, unique=False)
class Course(Base):
__tablename__ = "courses"
course_id = Column(String, primary_key=True)
course_name = Column(String, nullable=False)
level = Column(String, unique=False)
teacher_name = Column(ForeignKey("teachers.full_name"))
teacher = relationship("Teacher")
def main():
if Path("test_database.db").exists():
Path("test_database.db").unlink()
engine = create_engine("sqlite:///test_database.db")
Base.metadata.create_all(engine)
session = sqlalchemy.orm.Session(autocommit=False, autoflush=False, bind=engine)
teacher_1 = Teacher(full_name="Bob")
course_1 = Course(course_id=1, course_name="Course 1", level="beginner", teacher=teacher_1)
course_2 = Course(course_id=2, course_name="Course 2", level="advanced", teacher=teacher_1)
session.add_all([course_1, course_2])
session.commit()
if __name__ == "__main__":
main()