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

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": {
                   # In case you might want to allow doubles OR int, then add
                   # "int" to the bsonType array below:
                   "bsonType": [ "double" ],
                   "minimum": 0,
                   "description": "must be a double and is required"
                }
             }
      }
    }
    
    # Per the docs, args to command() require that the first kev/value pair
    # be the command string and its principal argument, followed by other
    # arguments.  There are two ways to do this:  Using an OrderDict:
    cmd = OrderedDict([('collMod', 'myColl'),
            ('validator', vexpr),
            ('validationLevel', 'moderate')]
    db.command(cmd)
    
    # Or, use the kwargs construct:
    # db.command('collMod','myColl', validator=vexpr, validationLevel='moderate')

    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()