Python / SQLAlchemy - load relation when foreign key is updated?

Question

I have a class:

class Chart(Base):
   __tablename__ = 'chart'
   id = C('chart_id', Integer, primary_key=True)
   element_id = C(Integer, ForeignKey('element.element_id'))
   element = relationship(Element)
   name = C(String)

   def __init__(self, name):
      self.name = name

Usage is pretty common,

chart = Chart('Some name')
chart.element_id = element_id

But chart.element is None after setting element_id. Is there any way to auto-load this relation for new object before flush/commit?

NPatel · Accepted Answer · 2011-10-10 05:15:38Z

6

The best option is

chart = Chart('Some name')
chart.element = element

Assign direct object to the relation ship. If you are assign element_id then until it flush it will be in memory. Internally it will fire a query SELECT * FROM ELEMENT WHERE ELEMENT.id = element_id but that element_id data is not store or it will be in memory.

So i suggest direct assign object if you don't want to flush.

Hope this will help you.

answered Oct 10, 2011 at 5:15

NPatel

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1 Comment

Victor Over a year ago

Thanks for the reponse. I'm using this way now. My function receives element_id, and I get element by myself to set it in a Chart object (flush is done internally). It looks it's the only one way.

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