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.

function Int8(key, options) {
  mongoose.SchemaType.call(this, key, options, 'Int8');
}
Int8.prototype = Object.create(mongoose.SchemaType.prototype);

// `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.
Int8.prototype.cast = function(val) {
  var _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;

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

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