var UserSchema = new mongoose.Schema({
    username: String,
    password: String,
    first: String,
    last: String,
    email: String,
    roles: [String],
    logs: [{
        type: Schema.Types.ObjectId,
        ref: 'Log'
    }]
});


var LogSchema = new mongoose.Schema({
    posted_by: { type: String, ref: 'User'},
    content:  String,
    date      : String,
});

var ResourcesSchema = new mongoose.Schema({
    name: String,
    serialnumber: String,
    modelno: String,
    description: String,
    logs: [LogSchema]
});

<select ng-model="selectedResource" ng-options="resource.name for resource in resources" class="form-control" >
                    </select>
                    <br/>
                    <div class="row">
                        <div class="col-xs-3">
                            {{selectedResource.logs}}
                        </div>

                    </div>
                    <br/>
                    <br/>


                    <textarea rows="3" cols="50" placeholder="content" ng-model="log.content">
                    </textarea>
                    <br/>
                    <br/>


                    <button class="btn btn-primary" ng-click="addLog()">Post</button>

app.controller("ActivitylogCtrl", function($scope, $http) {

    $http.get('/activitylog')
        .success(function(response) {
            $scope.resources = response;
    });

    $scope.all = function(){
        $http.get('/activitylog')
        .success(function(response) {
            var log = "";
            $scope.logs = response;
            $scope.log = "";
        });
    };

    $scope.addLog = function() {
        console.log($scope.log);
        $http.post('/activitylog', $scope.log)
        .success(function(response){
            $scope.logs.push(response);
            $scope.all();
        });
    };

    $scope.all();

});

app.post("/activitylog", function(req, res){
    var selectedResource = req.body.selectedResource;
    var content = req.body.content;
    var date = new Date().toISOString().replace(/T/,' ').replace(/..+/,'');
   Resources.findByIdAndUpdate(
    selectedResource,
        {$push: {"logs": {content: content, date: date}}},
        {safe : true, upsert: true},
        function(err, model) {
            console.log(err);
        }
   );
});