Set Managed Metadata Values via REST

Question

I am able to query and get an array of all my term names and guids within a Term Set, but now I want to be able to set these via REST. When I look at the structure in JSON the section with my Managed Metadata appears as follows. It seems like a sub-array

"TextField": "My Text",
"MMField": {
    "Label": "7",
    "TermGuid": "7d5e44d8-e5a7-4eb7-9735-7b51cea64aa8",
    "WssId": 7
},

Using AngularJS I have tried posting to it via the following:

 var itemEntry = new appItems;

        $scope.createEvent = function () {
             // Taxonomy Value Posting
            itemEntry.TextField = 'Hooray Text';
            itemEntry.MMField.Label = '7';
            itemEntry.MMField.TermGuid = '7d5e44d8-e5a7-4eb7-9735-7b51cea64aa8';
            itemEntry.MMField.WssId = '7';
            itemEntry.$save(function () {
                $location.path('/');
            });
        }

However, it is failing on the first option of MMField.Label as follows:

Unable to set property 'Label' of undefined or null reference

Using REST I should be able to hit the straight values and set this, but I must be missing something obvious. Any clues/what am I missing to hit the sub values within MMField?

Answer 1

It probably fails because you haven't set itemEntry.MMField = {};

Try using object literal notation (note __metadata):

itemEntry.MMField = { 
  __metadata: { type: "SP.Taxonomy.TaxonomyFieldValue" }, 
  Label: '7',
  TermGuid: "7d5e44d8-e5a7-4eb7-9735-7b51cea64aa8", 
  WssId: -1 
};

Update:

An alternative solution is to set HTTP request header Content-Type to application/json;odata=nometadata (ref blog and ref msdn).

Then the object literal notation would look like this:

temEntry.MMField = { 
  Label: "7", 
  TermGuid: "7d5e44d8-e5a7-4eb7-9735-7b51cea64aa8", 
  WssId: -1 
};

Answer 2

Thanks to @erikb, I needed the proper format of my code. I was using dot notation, but needed to hit the array as follows. Please note that I am using the nometadata option in my headers, so my JSON does not have the verbose aspects such as __metadata: { type: "SP.Taxonomy.TaxonomyFieldValue" }.

 // Create item
        var itemEntry = new appItems;

        $scope.createEvent = function () {
            console.log("Clicked");
            itemEntry.CategoryId = $scope.vm.selectedCategory.value;
            itemEntry.Title = $scope.vm.eventdescription;
            // Taxonomy Value Posting
            itemEntry.MMField = {
                Label: $scope.term.selected.termName,
                TermGuid: $scope.term.selected.termGUID,
                WssId: -1
            }
            itemEntry.$save(function () {
                $location.path('/');
            });
        }