flask sqlalchemy execute method every time object is updated

Question

what is the method name that gets executed every time a member of a class is updated?

for example, init is run when an object is instantiated:

class Foo(db.Model)
    id = db.Column(db.Integer, primary_key=True)
    description = db.Column(db.String(50))

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

i would like to add a method to this class that runs every time i update a Foo object.

after reading up on python classes here:

http://www.rafekettler.com/magicmethods.html

i thought that the method i was looking for would look something like the below (but haven't gotten it working yet):

class Foo(db.Model)
    id = db.Column(db.Integer, primary_key=True)
    description = db.Column(db.String(50))

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

    def __call__(self, description):
        print 'obj is getting updated!'
        self.description = description

thanks for the help!

Do you mean updated in database (asking because of the flask-sqlalchemy tag) or just the class property? — plaes
– plaes, Commented Jan 11, 2013 at 20:33

Audrius Kažukauskas · Accepted Answer · 2013-01-11 20:20:35Z

1

__call__ is used when you want to make the instances of your object callable, just like functions:

class Foo(object):
    def __init__(self, foo):
        self.foo = foo

    def __call__(self):
        return 'foo is {}!'.format(self.foo)

foo = Foo('bar')
print foo()    # Note that we're calling instance of Foo as if it was a function.

What you probably want is __setattr__, which is called when a value is assigned to object's attribute:

class Foo(db.Model):
    # ...

    def __setattr__(self, name, value):
        # Call the parent class method first.
        super(Foo, self).__setattr__(name, value)
        print 'Value {!r} was assigned to attribute {}'.format(value, name)

answered Jan 11, 2013 at 20:20

Audrius Kažukauskas

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