Handling one-to-one and one-to-many relationships in MongoDB can be done using references or embedding. The following example shows both ways, which are references for the model user and embedding for the comment model:

from pymodm import EmbeddedMongoModel, MongoModel, fields
 
class Comment(EmbeddedMongoModel):
    author = fields.ReferenceField(User)
    content = fields.CharField()
 
class Post(MongoModel):
    title = fields.CharField()
    author = fields.ReferenceField(User)
    revised_on = fields.DateTimeField()
    content = fields.CharField()
    comments = fields.EmbeddedDocumentListField(Comment)

Similar to Mongoid for Ruby, we can define relationships as being embedded or referenced, depending on our design decision.