ng-options完成后如何设置默认值？

Question

假设这是我的控制器：

function MainController(BaseInformation, baseInformationConstants) {
    var vm = this;
    getGenders();

    function getGenders() {
        vm.genders = BaseInformation.list({headerId: baseInformationConstants.genderId});
    }
}

和这个select标签，我想用ng-init为它设置默认值，但它没有用：

<select ng-init="vm.user.genderId = {id: vm.genders[0].id}"
        ng-model="vm.user.genderId"
        ng-options="gender.id as gender.topic for gender in vm.genders track by gender.id">
</select>