AngularJS: How to access scope from directive - angularjs-directive

Question

I'm using a directive to draw graphs:
drawGraph.directive "graph", ->
restrict: "E" # Use as element
scope: # Isolate scope
data: "=" # Two-way bind data to local scope
opts: "=?" # '?' means optional
template: "<div></div><div id='{{graph.id}}'></div>" # We need a div to attach graph to
link: (scope, elem, attrs) ->
graph = new Dygraph(elem.children()[0], scope.data, scope.opts)
While
<div id='{{graph.id}}'>
actually works in the partial, it returns
<div id></div>
when I use it in the template of the directive. Can anyone tell me why?
Update:
After the hint of #Marek, my directive now looks like this:
drawGraph.directive "graph", ->
restrict: "E" # Use as element
scope: # Isolate scope
data: "=" # Two-way bind data to local scope
opts: "=?" # '?' means optional
template: "<div></div><div class='legend'></div>" # We need a div to attach graph to
link: (scope, elem, attrs) ->
scope.opts.labelsDiv = elem.children()[0].getElementsByClassName("legend")[0]
scope.graph = new Dygraph(elem.children()[0], scope.data, scope.opts)
Options are added in the controller:
drawGraph.controller "MyCtrl", [ "myService", "$scope", (myService, $scope) ->
myService.async().then (d) ->
rawData = d
group = rawData
i = 0
while i < group.length
j = 0
while j < group[i].data.length
# Convert date
tmp = new Date(group[i].data[j][0])
group[i].data[j][0] = tmp
# Set draw options
group[i].opts =
labels: [ "x", "Your Price", "Market Price" ],
customBars: true,
labelsSeparateLines: "true",
hideOverlayOnMouseOut: false,
legend: "always",
showRangeSelector: true,
xAxisLabelWidth: 80,
++j
++i
$scope.graphs = group

Answer 1

Problem was that an isolated scope can't access the parent scope by default, so "id" needs to be defined in the scope of the directive.
drawGraph.directive "graph", [(graph) ->
restrict: "E"
scope:
data: "="
opts: "=?"
id: "="

Answer 2

You're not actually putting the graph into the scope.
The last line should be:
scope.graph = new Dygraph(elem.children()[0], scope.data, scope.opts)