Question

since four days I’m trying to figure out how to follow a reference from one to another class, starting from the class which is beeing referenced. In SQL-Django there is a related_name to achieve this…

For example I have this class:

class MyClass(Document):
    ...
    other_classes = ListField(ReferenceField(Other_Class))

and this one:

class Other_Class(Document):
    ...

Now I want to go from Other_Class to MyClass… Any ideas?

Thanks,

Ron

Answer 1

Here is a test case showing how to query it:

import unittest
from mongoengine import *


class StackOverFlowTest(unittest.TestCase):

    def setUp(self):
        conn = connect(db='mongoenginetest')

    def test_one_two_many(self):

        class MyClass(Document):
            other_classes = ListField(ReferenceField("OtherClass"))

        class OtherClass(Document):
            text = StringField()

        MyClass.drop_collection()
        OtherClass.drop_collection()

        o1 = OtherClass(text='one').save()
        o2 = OtherClass(text='two').save()
        m = MyClass(other_classes=[o1, o2]).save()

        # Lookup MyClass that has o1 in its other_classes
        self.assertEqual(m, MyClass.objects.get(other_classes=o1))

        # Lookup MyClass where either o1 or o2 matches
        self.assertEqual(m, MyClass.objects.get(other_classes__in=[o1, o2]))

The main question is do you need to store a list of references in the MyClass? It might be more efficient to store the relationship just on OtherClass..