I seem to have solved this: the update() function requires an array of objects as the argument, even if you just have one object to update, add it to an array. In my opinion, the function should check to see if the value it is receiving is an array or not and return an error before it carries on with the rest of the function. I can't see how I received a successful return from this function when it never worked and the argument supplied in the first place was wrong.