Code Summary: Schema Validation

To create a new "sales" collection schema validation, we use the createCollection method with the validator option. In this example, we combine a query operator, $and, and JSON schema to define the schema validation rules. $and checks the discounterPrice is lower than the item price for a given item and $jsonSchema ensures the items field is an array.

db.createCollection("sales", {
    validator: {
      "$and": [
        {
          "$expr": {
            "$lt": ["$items.discountedPrice", "$items.price"]
          }
        },
        {
          "$jsonSchema": {
            "properties": {
              "items": { "bsonType": "array" }
            }
           }
         }
       ]
     }
   }
 )

To find all the documents that do not match a validator expression use the following:

db.collection.find( { $nor: [ validator ] } )

This is the reviews validator used for our bookstore:

const bookstore_reviews_default = {
    bsonType: "object",
    required: [“_id”, "review_id", "user_id", "timestamp", "review", "rating"],
    additionalProperties: false,
    properties: {
        _id: { bsonType: "objectId" },
        review_id: { bsonType: "string" },
        user_id: { bsonType: "string" },
        timestamp: { bsonType: "date" },
        review: { bsonType: "string" },
        rating: {
            bsonType: "int",
            minimum: 0,
            maximum: 5,
        },
        comments: {
            bsonType: "array",
            maxItems: 3,
            items: {
                bsonType: "object",
            },
        },
    },
};

To enable or update schema validation for an existing collection use the collMod command providing the validator option. In our example, we used the $jsonSchema operator to build the validator. We also overrided the default validation level and validation action options to be strict and error respectively:

const schema_validation = { $jsonSchema: bookstore_reviews_default };

db.runCommand({
    collMod: "reviews",
    validator: schema_validation,
    validationLevel: "strict",
    validationAction: "error",
});