Testing return value of SQLAlchemy parent-child relationship query

问题

Say I have two models set up like so:

class ParentFoo(SqlBase):
  __tablename__ = "parents"

  id = Column(String, primary_key=True)
  children = relationship("ChildFoo", backref="parents")

class ChildFoo(SqlBase):
  __tablename__ = "children"

  id = Column(String, primary_key=True)

Now in a request handler, say I want to get all children entities from the database given a parent:

class RequestHandler():

  def get(self, parent_id):
    parent = database.query(parent_id)
    children = parent.children
    send_response(children)

The SQLAlchemy ORM API allows this type of query. The problem for me is when I'm writing my tests. I have a generic RequestHandler class that takes a ParentFoo and a ChildFoo class as arguments in the constructor. So my request handler class actually looks like this:

class GenericRequestHandler():

  def __init__(self, parent_class, child_class):
    self.parent_class = parent_class
    self.child_class = child_class

  def get(self, parent_id):
    parent = database.query(self.parent_class, parent_id)
    children = parent.getattr(self.child_class.__tablename__, None)

As long as the column name on the parent matches the __tablename__ for the child entities, this will work. I enforce this convention. The problem is testing this.

Python's mock library doesn't seem to provide for return values on attribute lookups and I don't want to mock out the getattr function, because it's used elsewhere in my get method.

Any thoughts?

Edit 1: Regarding my comment about attribute lookups: I can mock out a function and provide a return value.

mocked_function.return_value = my_desired_value

But how do I mock out an attribute?

mocked_object.attribute_of_interest = my_desired_value

Edit 2: In my tests, I provide MagicMock objects to the constructor for the parent and child classes, and I set a MagicMock object to be returned by the call to database.query:

parent_class_mock = MagicMock()
child_class_mock = MagicMock()
parent_entity = MagicMock()
type(parent_entity).getattr = PropertyMock(return_value=[child_entity])
database.query.return_value = parent_entity

class ConcreteRequestHandler(GenericRequestHandler):
  def __init__(self, parent_class, child_class):
    super(ConcreteRequestHandler, self).__init__(parent_class, child_class)

As you can see, I tried to use mock's PropertyMock to set an attribute. When I ran the test, I got an error saying 'list' object not callable. Please see this SO question I asked related to this.

来源：https://stackoverflow.com/questions/36782736/testing-return-value-of-sqlalchemy-parent-child-relationship-query

标签

python

testing

sqlalchemy