Populate dojo ItemFileReadStore from Grails "render as JSON"

I have created a method in my controller that will give me a JSON "file" if I browse to that URL directly. It is only in memory, not on disk, as it is generated at the time you hit the URL. I am trying to use this as my data store for a dojo tree, however, when I am using this, the Tree never populates, it just sits there with the "waiting" cursor. Is there a different way to populate the data for the Tree?

Here is the code below. "getFilterTree" returns a开发者_StackOverflow社区 rendered JSON object in grails

       var store = new dojo.data.ItemFileReadStore({
           url: "/SkillsDB/search/getFilterTree"
       });

       var treeModel = new dijit.tree.ForestStoreModel({
           store: store,
           query: {
               "type":"cat"
           },
           rootId: "root",
           rootLabel: "Filter Categories",
           childrenAttrs: ["children"]
       });

       new dijit.Tree({
           model: treeModel
       },
       "treeOne");

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It should definetely work.

For ItemFileReadStore, your json should comply with the structures shown in this page : http://dojotoolkit.org/reference-guide/dojo/data/ItemFileReadStore.html