I changed your directive a bit, but this is how you get that sort of functionality.
FIDDLE
If you're interested in AngularJS I would highly recommend the John papa styleguide.
https://github.com/johnpapa/angular-styleguide
It will get you using syntax like controllerAs and will help make your code cleaner.
HTML
<body ng-app="myApp" ng-controller="MainCtrl">
<div>
Original name: {{mandat.name}}
</div>
<my-directive mandat="mandat"></my-directive>
</body>
JS
var app = angular.module('myApp', []);
app.controller('MainCtrl', MainController);
function MainController($scope) {
$scope.mandat = {
name: "John",
surname: "Doe",
person: { id: 1408, firstname: "sam" }
};
}
app.directive('myDirective', MyDirective);
function MyDirective() {
return {
restrict: 'E',
template: "<div><input type='text' ng-model='mandat.person.firstname' /><button ng-click='updateparent()'>click</button></div>",
replace: true,
scope: {
mandat: "="
},
controller: function($scope) {
$scope.updateparent = function() {
$scope.mandat.name = "monkey";
}
}
}
}