Tips for JSON Schema Validation

_id Field and additionalProperties: false

When you specify additionalProperties: false in your JSON schema, MongoDB rejects documents that contain fields not included in your schema's properties object.

Because all objects contain an automatically-generated _id field, when you set additionalProperties: false, you must include the _id field in your properties object. If you don't, all documents are rejected.

For example, with this validation, no documents are valid:

{
  "$jsonSchema": {
    "required": [ "_id", "storeLocation" ],
    "properties": {
      "storeLocation": { "bsonType": "string" }
    },
    "additionalProperties": false
  }
}

This validation ensures that storeLocation is a string. However, the properties object does not contain an _id field.

To allow documents in the collection, you must update the properties object to include an _id field:

{
  "$jsonSchema": {
    "required": [ "_id", "storeLocation" ],
    "properties": {
      "_id": { "bsonType": "objectId" },
      "storeLocation": { "bsonType": "string" }
    },
    "additionalProperties": false
  }
}

Validation for null Field Values

Your application may be configured to set missing field values to null, instead of not including those fields in the object sent to the collection.

If your schema validates data types for a field, to insert documents with a null value for that field, you must explicitly allow null as a valid BSON type.

For example, this schema validation does not allow documents where storeLocation is null:

db.createCollection("sales",
   {
      validator:
         {
            "$jsonSchema": {
               "properties": {
                  "storeLocation": { "bsonType": "string" }
               }
            }
         }
    }
 )

With the preceding validation, this document is rejected:

db.store.insertOne( { storeLocation: null } )

Alternatively, this schema validation allows null values for storeLocation:

db.createCollection("store",
   {
      validator:
         {
            "$jsonSchema": {
               "properties": {
                  "storeLocation": { "bsonType": [ "null", "string" ] }
               }
            }
         }
    }
 )

With the preceding validation, this document is allowed:

db.store.insertOne( { storeLocation: null } )