Angular指令范围继承/隔离

我有一个指令，从一个集合建立动态表。它有两种类型的列，复选框和下拉框。但是，在指令级别上无法正确解析范围。它们被定义为"未定义"。我还需要从控制器绑定下拉选项。

<div ng-app="myApp">
<div ng-controller="MyCtrl">
  <ui-table source="students">
      <check-col title="passed" field="passed"/>
      <drop-down-col title="std" field="std" />
    </ui-table>
</div>
</div>

角js

var myApp = angular.module('myApp',[]);
myApp.directive("uiTable", function ($compile) {
        var generateTableHtml = function ($scope) {
            // header
            var html = "<table class='table table-condensed table-bordered table-responsive'><thead class='thead12'><tr class='active'>";
            angular.forEach($scope.columns, function (col) {
                debugger;
                html += "<th scope='col'" +
                    (col.cssClass ? " class='" + col.cssClass + "'" : "") +
                    ">" + col.title + "</th>";
            });
            html += "</tr></thead><tbody>";
            // body
            html += "<tr ng-repeat='item in dataSource'>";
            angular.forEach($scope.columns, function (col) {
                html += "<td" + (col.cssClass ? " class='" + col.cssClass + "'" : "") + ">";
                if (col.type === ColumnType.Check) {
                    html += "<input type='checkbox' ng-model='item." + col.dataField + "'/>";
                } else if (col.type === ColumnType.DropDown) {
                    html += "<select ng-model='item." +col.dataField + "' ng-options = 'option.Value for option in dataOptions'></select>";
                }
                html += "</td>";
            });
            html += "</tr>";
            html += "</tbody></table>";
            return html;
        };
        return {
            restrict: "E",
            replace: true,
            transclude: true,
            scope: {
                dataSource: "=source"
            },
            controller: function ($scope) {
                $scope.columns = [];
                this.addColumn = function (col) {
                    $scope.columns.splice(0, 0, col);
                };
            },
            template: "<div ng-transclude></div>",

            compile: function () {
                return function ($scope, $elem) {
                    $elem.html(generateTableHtml($scope));
                    $compile($elem.contents())($scope);
                };
            }
        };
    });
myApp.directive("checkCol", function () {
        return {
            require: "^uiTable",
            restrict: "E",
            replace: true,
            scope: {
                title: "@title",
                cssClass: "@class",
                dataField: "@field"
            },
            link: function ($scope, element, attrs, tableControl) {
                $scope.type = ColumnType.Check;
                tableControl.addColumn($scope);
            }
        };
});
myApp.directive("dropDownCol", function() {
    return {
        require: "^uiTable",
        restrict: "E",
        replace: true,
        scope: {
            title: "@title",
            cssClass: "@class",
            dataField: "@field"
        },
        link: function($scope, element, attrs, tableControl) {
            $scope.type = ColumnType.DropDown;
            tableControl.addColumn($scope);
        }
    };
});
//myApp.factory('myService', function() {});
var ColumnType = { Check: 1, DropDown: 2 };
myApp.controller('MyCtrl', function($scope) {
    $scope.students = [{id:1, std:10, passed: true}, {id:2, std:9, passed: false}];
$scope.stds= [{Value: 10, Name: '10the std'},{Value: 9, Name: '9the std'},{Value: 8, Name: '8the std'}];
});

JSFIDDLE