Creating a Basic Custom Schema Type

New in Mongoose 4.4.0: Mongoose supports custom types. Before you reach for a custom type, however, know that a custom type is overkill for most use cases. You can do most basic tasks with custom getters/setters, virtuals, and single embedded docs.

Let's take a look at an example of a basic schema type: a 1-byte integer. To create a new schema type, you need to inherit from mongoose.SchemaType and add the corresponding property to mongoose.Schema.Types. The one method you need to implement is the cast() method.

class Int8 extends mongoose.SchemaType {
  constructor(key, options) {
    super(key, options, 'Int8');

  // `cast()` takes a parameter that can be anything. You need to
  // validate the provided `val` and throw a `CastError` if you
  // can't convert it.
  cast(val) {
    let _val = Number(val);
    if (isNaN(_val)) {
      throw new Error('Int8: ' + val + ' is not a number');
    _val = Math.round(_val);
    if (_val < -0x80 || _val > 0x7F) {
      throw new Error('Int8: ' + val +
        ' is outside of the range of valid 8-bit ints');
    return _val;

// Don't forget to add `Int8` to the type registry
mongoose.Schema.Types.Int8 = Int8;

const testSchema = new Schema({ test: Int8 });
const Test = mongoose.model('CustomTypeExample', testSchema);

const t = new Test();
t.test = 'abc';
assert.equal(t.validateSync().errors['test'].name, 'CastError');
  'Cast to Int8 failed for value "abc" at path "test"');
  'Int8: abc is not a number');