Mongoose Validation

Mongoose validation checks document values before saving them.

It helps keep application data consistent.

Basic validation

const userSchema = new mongoose.Schema({
  name: {
    type: String,
    required: true,
    minlength: 2,
  },
  email: {
    type: String,
    required: true,
    lowercase: true,
  },
  age: {
    type: Number,
    min: 18,
  },
})

Custom validation

const productSchema = new mongoose.Schema({
  price: {
    type: Number,
    validate: {
      validator(value) {
        return value >= 0
      },
      message: 'Price cannot be negative',
    },
  },
})

Validation is not enough

Mongoose validation runs in the application.

It does not replace:

• database indexes,
• authorization,
• request validation,
• business rules,
• unique constraint handling.

Common mistake

Do not rely only on Mongoose validation for API input.

Validate request input before it reaches the database layer too.

Interview answer

Mongoose validation enforces rules on documents before saving, such as required fields, min/max values, enum values, and custom validators. It helps maintain data consistency, but it should be used along with request validation, indexes, and proper business logic.