In our original poetry application example we declared the schema type for our title as a String:

const poemSchema = new mongoose.Schema({
  title: String
})

Often, we want to specify more than just the type of a path — we can use validators to ensure other aspects of a document’s input value.

Validators

Data validation is intended to provide guarantees about user input. Mongoose has several built-in validators.

You can add required validators to our Schema in an object that you pass to the path:

const poemSchema = new mongoose.Schema({
  title: {
    type: String,
    required: true
  },
  body: {
    type: [String],
    required: true
  },
  published: {
    type: Boolean,
    required: true
  },
})

In the example above, we set the schema type and required attributes for the title, body, and published paths. If the required property is true, then it is a required field when you save to the database.

If you save a document with an invalid path value, you will receive this error message Path `title` is required.. You can define a custom error message like this:

const poemSchema = new mongoose.Schema({
  title: {
    type: String,
    required: 'Title is required!'
  }
})

You can learn more about mongoose validators in their documentation.