Fix Python – method of iterating over sqlalchemy model’s defined columns?


Asked By – Rick

I’ve been trying to figure out how to iterate over the list of columns defined in a SQLAlchemy model. I want it for writing some serialization and copy methods to a couple of models. I can’t just iterate over the obj.__dict__ since it contains a lot of SA specific items.

Anyone know of a way to just get the id and desc names from the following?

class JobStatus(Base):
    __tablename__ = 'jobstatus'

    id = Column(Integer, primary_key=True)
    desc = Column(Unicode(20))

In this small case I could easily create a:

def logme(self):
    return {'id':, 'desc': self.desc}

but I’d prefer something that auto-generates the dict (for larger objects).

Now we will see solution for issue: method of iterating over sqlalchemy model’s defined columns?


You could use the following function:

def __unicode__(self):
    return "[%s(%s)]" % (self.__class__.__name__, ', '.join('%s=%s' % (k, self.__dict__[k]) for k in sorted(self.__dict__) if '_sa_' != k[:4]))

It will exclude SA magic attributes, but will not exclude the relations. So basically it might load the dependencies, parents, children etc, which is definitely not desirable.

But it is actually much easier because if you inherit from Base, you have a __table__ attribute, so that you can do:

for c in JobStatus.__table__.columns:
    print c

for c in JobStatus.__table__.foreign_keys:
    print c

See How to discover table properties from SQLAlchemy mapped object – similar question.

Edit by Mike: Please see functions such as Mapper.c and Mapper.mapped_table. If using 0.8 and higher also see Mapper.attrs and related functions.

Example for Mapper.attrs:

from sqlalchemy import inspect
mapper = inspect(JobStatus)
for column in mapper.attrs:
    print column.key

This question is answered By – van

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