Initial commit.

.gitignore

+*.pyc
+*.pyo
+
+.idea
+.buildozer
+bin

database.py

+from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.orm import sessionmaker, relationship
+
+
+Persisted = declarative_base()
+
+
+class Person(Persisted):
+    __tablename__ = 'people'
+    person_id = Column(Integer, primary_key=True)
+    name = Column(String(256), nullable=False)
+    supervisor_id = Column(Integer, ForeignKey('people.person_id', ondelete='CASCADE'))
+    mentor_id = Column(Integer, ForeignKey('people.person_id', ondelete='CASCADE'))
+    # Because there are multiple keys the relationship could use, we have to specify the foreign key to use and the key
+    # to match it to (in this case a primary key).
+    supervisor = relationship('Person', foreign_keys=[supervisor_id], remote_side=[person_id], back_populates='supervisees')
+    mentor = relationship('Person', foreign_keys=[mentor_id], remote_side=[person_id], back_populates='mentees')
+    # For the reverse relationships (the ones with uselist=True), the key to match to is implicitly the primary key.
+    supervisees = relationship('Person', foreign_keys=[supervisor_id], uselist=True, back_populates='supervisor')
+    mentees = relationship('Person', foreign_keys=[mentor_id], uselist=True, back_populates='mentor')
+
+
+class Database(object):
+    @staticmethod
+    def construct_mysql_url(authority, port, database, username, password):
+        return 'mysql+mysqlconnector://{username}:{password}@{authority}:{port}/{database}' \
+            .format(authority=authority, port=port, database=database, username=username, password=password)
+
+    @staticmethod
+    def construct_in_memory_url():
+        return 'sqlite:///'
+
+    def __init__(self, url):
+        self.engine = create_engine(url)
+        self.Session = sessionmaker()
+        self.Session.configure(bind=self.engine)
+
+    def ensure_tables_exist(self):
+        Persisted.metadata.create_all(self.engine)
+
+    def create_session(self):
+        return self.Session()

installer.py

+# -*- coding: utf-8; -*-
+
+from sys import stderr
+
+from sqlalchemy.exc import SQLAlchemyError
+
+from database import Database, Person
+
+
+def add_starter_data(session):
+    alice = Person(name='Alice')
+    bob = Person(name='Bob', mentor=alice)
+    carol = Person(name='Carol', supervisor=alice, mentor=bob)
+    session.add(alice)
+    session.add(bob)
+    session.add(carol)
+
+
+def main():
+    try:
+        url = Database.construct_mysql_url('localhost', 3306, 'people', 'root', 'cse')
+        database = Database(url)
+        database.ensure_tables_exist()
+        print('Tables created.')
+        session = database.create_session()
+        add_starter_data(session)
+        session.commit()
+        print('Records created.')
+    except SQLAlchemyError as exception:
+        print('Database setup failed!', file=stderr)
+        print('Cause: {exception}'.format(exception=exception), file=stderr)
+        exit(1)
+
+
+if __name__ == '__main__':
+    main()