title: Alembic does not add Cascade information in autogenerate?
body: <p>Here is my <code>Budget</code> schema</p>
  
  <pre><code>class Budget(db.Model):
      __tablename__ = 'budgets'
      # noinspection PyRedeclaration
      uuid = Column('uuid', GUID(), default=uuid.uuid4, primary_key=True,
                    unique=True)
      user_id = Column(GUID(), ForeignKey('users.uuid'), nullable=False)
      user = relationship('User', backref='budgets')
      created_on = Column('created_on', sa.types.DateTime(timezone=True),
                          nullable=False)
  </code></pre>
  
  <p>and <code>BudgetCategories</code></p>
  
  <pre><code>class BudgetCategory(db.Model):
      __tablename__ = 'budget_categories'
      # noinspection PyRedeclaration
      uuid = Column('uuid', GUID(), default=uuid.uuid4, primary_key=True,
                    unique=True)
      budget_id = Column(GUID(), ForeignKey('budgets.uuid'), nullable=False)
      budget = relationship('Budget', backref='budgetCategories',
                            cascade="all, delete-orphan", single_parent=True)
      category = Column('category', sa.types.String, nullable=True)
      parent_category = Column('parent_category', sa.types.String, nullable=True)
      amount = Column('amount', Numeric(10, 2), nullable=False)
      recurring = Column('recurring', sa.types.Boolean,
                         nullable=False)
      created_on = Column('created_on', sa.types.DateTime(timezone=True),
                          nullable=False)
  </code></pre>
  
  <p>when I generate alembic migration script I do</p>
  
  <pre><code> alembic revision --autogenerate -m 'add_budgetCategories_Jan252014'
  </code></pre>
  
  <p>and I get</p>
  
  <pre><code>def upgrade():
  ### commands auto generated by Alembic - please adjust! ###
      op.create_table('budgets',
      sa.Column('uuid', UUID(), nullable=False),
      sa.Column('user_id', UUID(), nullable=False),
      sa.Column('created_on', sa.DateTime(timezone=True), nullable=False),
      sa.ForeignKeyConstraint(['user_id'], ['users.uuid'], ),
      sa.PrimaryKeyConstraint('uuid'),
      sa.UniqueConstraint('uuid')
      )
      ### end Alembic commands ###
  </code></pre>
  
  <p>Then I do</p>
  
  <pre><code> alembic revision --autogenerate -m 'add_budgetCategories_Jan252014'
  </code></pre>
  
  <p>and I get</p>
  
  <pre><code>def upgrade():
  ### commands auto generated by Alembic - please adjust! ###
      op.create_table('budget_categories',
      sa.Column('uuid', sa.GUID(), nullable=False),
      sa.Column('budget_id', sa.GUID(), nullable=False),
      sa.Column('category', sa.String(), nullable=True),
      sa.Column('parent_category', sa.String(), nullable=True),
      sa.Column('amount', sa.Numeric(precision=10, scale=2), nullable=False),
      sa.Column('recurring', sa.Boolean(), nullable=False),
      sa.Column('created_on', sa.DateTime(timezone=True), nullable=False),
      sa.ForeignKeyConstraint(['budget_id'], ['budgets.uuid'], ),
      sa.PrimaryKeyConstraint('uuid'),
      sa.UniqueConstraint('uuid')
      )
      ### end Alembic commands ###
  </code></pre>
  
  <p><strong>Question</strong>  </p>
  
  <p>Why did alembic not generate syntax for <code>ON CASCADE DELETE</code>? I guess I am missing things, but not sure what?  Can someone please help here?</p>