Does Pymongo have validation rules built in?

Question

I am trying to validate an inserted document against a schema, and was trying to find a way to validate the inserted document.

There are libraries like MongoEngine that say they do the work, but is there a way to do document validation directly via pymongo ?

Answer 1

MongoDB supports document validation at the engine level so you'll pick it up via pymongo. You declare your "schema" (rules actually) to the engine. Here's a great place to start: https://docs.mongodb.com/manual/core/document-validation/

Answer 2

The python driver docs are indeed a little light on how to use the db.command. Here is a complete working example:

from pymongo import MongoClient
from collections import OrderedDict
import sys

client = MongoClient()   # supply connection args as appropriate 
db = client.testX

db.myColl.drop()

db.create_collection("myColl")  # Force create!

#  $jsonSchema expression type is prefered.  New since v3.6 (2017):
vexpr = {"$jsonSchema":
  {
         "bsonType": "object",
         "required": [ "name", "year", "major", "gpa" ],
         "properties": {
            "name": {
               "bsonType": "string",
               "description": "must be a string and is required"
            },
            "gender": {
               "bsonType": "string",
               "description": "must be a string and is not required"
            },
            "year": {
               "bsonType": "int",
               "minimum": 2017,
               "maximum": 3017,
               "exclusiveMaximum": False,
               "description": "must be an integer in [ 2017, 3017 ] and is required"
            },
            "major": {
               "enum": [ "Math", "English", "Computer Science", "History", None ],
               "description": "can only be one of the enum values and is required"
            },
            "gpa": {
               "bsonType": [ "double" ],
               "minimum": 0,
               "description": "must be a double and is required"
            }
         }
  }
}

query = [('collMod', 'myColl'),
        ('validator', vexpr),
        ('validationLevel', 'moderate')]
query = OrderedDict(query)
db.command(query)

try:
    db.myColl.insert({"x":1})
    print "NOT good; the insert above should have failed."
except:
    print "OK. Expected exception:", sys.exc_info()    

try:
    okdoc = {"name":"buzz", "year":2019, "major":"Math", "gpa":3.8}
    db.myColl.insert(okdoc)
    print "All good."
except:
    print "exc:", sys.exc_info()