from sqlalchemy import *from migrate import *from migrate.changeset import *from sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy.orm import relation, deferred, mapper, backrefBase = declarative_base()Base.metadata.bind = migrate_engineclass User(Base):    __tablename__ = "users"        id = Column(Integer, primary_key=True)    username = Column(String(20), unique=True)    email = Column(String(128))    password = Column(String(20))    settings = Column(PickleType())    private_project = Column(String(50))    projects = relation('Project', backref='owner')class Project(Base):    __tablename__ = "projects"    id = Column(Integer, primary_key=True)    name = Column(String(60), unique=True)    user_id = Column(Integer, ForeignKey('users.id'))class File(Base):    __tablename__ = "files"        id = Column(Integer, primary_key=True)    name = Column(String(700), unique=True)    saved_size = Column(Integer)    data = deferred(Column(Binary))    edits = deferred(Column(PickleType))    dir_id = Column(Integer, ForeignKey('directories.id'))    dir = relation('Directory', backref="files")quota = Column('quota', Integer, default=10)amount_used = Column('amount_used', Integer, default=0)user_table = User.__table__utc = user_table.cfile_table = File.__table__ftc = file_table.cproject_table = Project.__table__ptc = project_table.cdef upgrade():    # Upgrade operations go here. Don't create your own engine; use the engine    # named 'migrate_engine' imported from migrate.    quota.create(user_table)    amount_used.create(user_table)    user_table.update().execute(quota=15)    query = select([utc.id, func.sum(ftc.saved_size)])    query = query.where(ptc.user_id==utc.id)    query = query.where("files.name like projects.name || '/%'")    query = query.group_by(utc.id)    result = query.execute()    for row in list(result):        query = user_table.update().where(utc.id==row[0])        query.execute(amount_used=row[1])    def downgrade():    # Operations to reverse the above upgrade go here.    # sqlite doesn't support this operation, sorry!    quota.drop(user_table)    amount_used.drop(user_table)