KendoUI grid with custom dropdown column passing whole object instead of Id

I am using Kendo frontend with Angular / Breeze. I have an editable grid with one column being a dropdown. Everything works fine until rescue occurs. The problem is that my otat call expects:

Id (guid), Name, Description, CategoryId (guid)

When the dropdown changes, it runs the save command and is sent back like this:

Id (guid), Name, Description, Category (categoryId, Name, Desc)

Where and how to make a grid to send only the categoryId instead of the whole category object?

    vm.columns = [
        { field: 'name', title: 'name' },
        { field: 'desc', title: 'description' },
        {
            field: 'categoryId',
            title: 'group',
            template: getCategory,
            editor: categoryDropDown
        }
    ];

    function categoryDropDown(container, options) {
        $('<input data-text-field="categoryName" data-value-field="categoryId" data-bind="value:' + options.field + '"/>')
            .appendTo(container)
            .kendoDropDownList({
                dataTextField: "categoryName",
                dataValueField: "categoryId",
                dataSource: vm.categories
            });
    }

    function getCategory(item) {
        for (var i = 0, length = vm.category; i < length; i++) {
            console.log(vm.categories[i].categoryId);
            if (vm.categories[i].categoryId === item.categoryId) {
                return vm.categories[i].categoryName;
            }
        }
        return '';
    }

      

        
        
        
      

    

Here is the schema for the main data source:

     schema: {
            model: {
                id: 'Id',
                fields: {
                    categoryName: { editable: true },
                    categoryDesc: { editable: true },
                    categoryId: { editable: true }
                }
            }
        }