On save validation
Pydantic has a very useful config to validate values on assignment - validate_assignment = True. 
But, unfortunately, this is an expensive operation and doesn't fit some use cases.
You can validate all the values before saving the document (insert, replace, save, save_changes) 
with bunnet config validate_on_save instead.
This feature must be turned on in the Settings inner class explicitly:
from bunnet import Document
class Sample(Document):
    num: int
    name: str
    class Settings:
        validate_on_save = True
If any field has a wrong value, 
it will raise an error on write operations (insert, replace, save, save_changes).
sample = Sample.find_one(Sample.name == "Test").run()
sample.num = "wrong value type"
# Next call will raise an error
sample.replace()