MongoDB - Schema Validation

In MongoDB, schema validation allows you to enforce specific rules on the structure and content of documents within a collection. While MongoDB is schema-less, schema validation provides a way to ensure that documents meet certain criteria. Validation rules are defined using JSON Schema.

Here's an overview of schema validation in MongoDB:

Basic Schema Validation:

1. Create a Validation Rule:

   • Define a JSON Schema that describes the expected structure of documents.

   {
     $jsonSchema: {
       bsonType: "object",
       required: ["name", "email"],
       properties: {
         name: {
           bsonType: "string",
           description: "must be a string and is required"
         },
         email: {
           bsonType: "string",
           pattern: "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$",
           description: "must be a string and match the regular expression pattern"
         }
       }
     }
   }

2. Apply Validation Rule to a Collection:

   • Use the collMod command to apply the validation rule to a collection.

   db.runCommand({
     collMod: "users",
     validator: {
       $jsonSchema: {
         bsonType: "object",
         required: ["name", "email"],
         properties: {
           name: {
             bsonType: "string",
             description: "must be a string and is required"
           },
           email: {
             bsonType: "string",
             pattern: "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$",
             description: "must be a string and match the regular expression pattern"
           }
         }
       }
     },
     validationLevel: "moderate",  // Options: "off", "strict", "moderate"
     validationAction: "error"     // Options: "error", "warn"
   });

Validation Level and Action:

• Validation Level:

  • "off": No validation (default).
  • "strict": Apply strict validation rules.
  • "moderate": Apply rules, but allow existing documents that do not meet the validation rules.

• Validation Action:

  • "error": Reject documents that do not meet validation rules.
  • "warn": Log a warning but allow documents that do not meet validation rules.

Example:

db.createCollection("users", {
  validator: {
    $jsonSchema: {
      bsonType: "object",
      required: ["name", "email"],
      properties: {
        name: {
          bsonType: "string",
          description: "must be a string and is required"
        },
        email: {
          bsonType: "string",
          pattern: "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$",
          description: "must be a string and match the regular expression pattern"
        }
      }
    }
  }
});

In this example, the users collection is created with a validation rule that requires documents to have name and email fields, and the email field must match a specific pattern.