old_contents: from sqlalchemy import Column, Integer, String
  from sqlalchemy.ext.declarative import declarative_base
  from sqlalchemy.schema import UniqueConstraint
  
  Base = declarative_base()
  
  class Store(Base):
      __tablename__ = 'store'
      id = Column(Integer, primary_key=True, autoincrement=True)
      key = Column(String)
      tag = Column(String)
      value = Column(String)
      __table_args__ = (UniqueConstraint('key', 'tag'),)
  
      def __unicode__(self):
          return unicode(key)
  
new_contents: from sqlalchemy import Column, Integer, String
  from sqlalchemy.ext.declarative import declarative_base
  from sqlalchemy.schema import PrimaryKeyConstraint
  
  Base = declarative_base()
  
  class Store(Base):
      __tablename__ = 'store'
      key = Column(String)
      tag = Column(String)
      value = Column(String)
      __table_args__ = (PrimaryKeyConstraint('key', 'tag'),)
  
      def __unicode__(self):
          return unicode(key)
  
subject: Make tag and key be a composite primary key