Schema Validation in MongoDB

What is Schema Validation?

MongoDB's schema validation guarantees that documents inserted into a collection fulfill the user-defined requirements or constraints. This feature contributes to data integrity and consistency inside the database.

When Should You Use Schema Validation?

• When you understand your application's structure and data requirements, use schema validation.
• Avoid schema validation during the testing phase of a new application, especially if the incoming data is unpredictable and the structure is unclear.
• Use schema validation to impose rules on specific fields, hence assuring data consistency and integrity.
• For example, in a collection that stores usernames as strings, schema validation might prohibit usernames from being stored with other data types, hence maintaining data homogeneity.
• Schema validation ensures data quality by enforcing criteria such as data types, sizes, and formats, which improves database reliability and consistency.

When does MongoDB validate data?

• MongoDB applies schema validation to changes and inserts in collections.
• Only new documents that are inserted into pre-existing, non-empty collections with validation rules are validated.
• Existing documents in a collection are not validated until they have been changed.
• Use the 'collMod' command to modify existing schema validation rules.
• MongoDB ensures data integrity through validation while also providing flexibility for handling existing data.

Validation Rules

• When creating or modifying a collection, use the validator option to provide validation requirements.
• The validator option specifies a query phrase that validates documents as they are added or changed to the collection.
• The validation criteria can be defined using MongoDB query operators and expressions.

Validation Actions

Validation actions specify what action to perform when a document violates the validation rules. The actions can be error, warn, or off.

• Error: The document failed validation and will not be inserted or changed.
• Warn: The document will be inserted or changed, but a warning will be issued.
• Off: No validation will occur.

Implementation of Schema Validation

• JSON Schema Validation: Sets validation criteria with the $jsonSchema operator.
• On Collection Creation: When creating a collection, use the validator option along with the database.createCollection().
• On Existing Collections: On existing collections, use the collMod command together with the validator option.

Validation Levels

• Strict (default): Validate all inserts and updates.
• Moderate: Validates inserts and modifications to documents that currently adhere to the schema.

Benefits of Schema Validation

• Prevents unexpected data types: Prevents invalid data from entering the collection (for example, password as an image).
• Ensures data integrity: Protects against accidental errors during data entry.
• Enforces data standards: Ensures a well-defined data model in your application.