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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) {, 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('Test', testSchema);

    var 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');