How to fix MongoServerError: Document failed validation in MongoDB

try {
  await collection.insertOne({ name: "John", age: "25" }); // age should be number
} catch (error) {
  console.log('Error code:', error.code); // 121
  console.log('Error info:', JSON.stringify(error.errInfo, null, 2));
  // Shows which field and why it failed
}

const db = client.db('myDatabase');
const collections = await db.listCollections({ name: 'myCollection' }).toArray();
const validator = collections[0]?.options?.validator;

console.log('Current validator:', JSON.stringify(validator, null, 2));

db.getCollectionInfos({ name: "myCollection" })[0].options.validator

// ❌ Fails validation
await collection.insertOne({ name: "John" });

// ✅ Includes required email field
await collection.insertOne({
  name: "John",
  email: "[email protected]"
});

// ❌ Age as string
await collection.insertOne({ name: "John", age: "25" });

// ✅ Age as number
await collection.insertOne({ name: "John", age: 25 });

// ❌ Age outside allowed range
await collection.insertOne({ name: "John", age: 150 });

// ✅ Age within valid range
await collection.insertOne({ name: "John", age: 25 });

await db.command({
  collMod: 'myCollection',
  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 valid email and is required'
        },
        age: {
          bsonType: 'int',
          minimum: 0,
          maximum: 120,
          description: 'must be an integer between 0 and 120'
        }
      }
    }
  },
  validationLevel: 'strict',
  validationAction: 'error'
});

await db.command({
  collMod: 'myCollection',
  validationLevel: 'moderate' // Only validates new inserts and updates to valid docs
});