Schema validation

MongoDB schema validation allows us to enforce rules on documents within a collection, ensuring data consistency.

Skipping validation during the early stages of development can speed up the process..
Once our data model is established, we can enforce validations to ensure data consistency.

Validator

Applied validator on creation

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

Applied validator after creation

Objects created before enforcing the validator won't be affected by new validations.

db.runCommand({
    collMod: "reviews", // collection to modify
    validator: bookstore_reviews_default, // validator specified in the example below
    validationLevel: "strict",
    validationAction: "error", // rejects operation
});

Check non validated documents

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

Validation mode

Specifies when rules are applied.

Strict: rejects any document that do not match the validation.
Moderate: only validate fields that match the schema but not extra fields.

Validation actions

What needs to be done after validation fails.

Warn. Logs a warning but the operation is resolved.
Error. Rejects operation.

Validator example

const bookstore_reviews_default = {
    $jsonSchema:{
        bsonType: "object", // type of the field
        required: [“_id”, "review_id", "user_id", "timestamp", "review", "rating"], // required fields
        additionalProperties: false, // can't add new properties that are not listed
        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",
                },
            },
        },
    }
};