Angular JS：选择菜单中带有ng-repeat选项的默认值

Question

I have tried to follow the examples on the Angular 1.4.12 docs and what I've found here, still I cannot set a default value for a select menu.

My html (using controller as of mob ):

<select name="userCurrencyType" 
   ng-model="mob.currencyType" 
   ng-options="s.name + ' - ' + s.code for s in mob.currencyTypes"></select>

Which correctly gives me a menu like:

Where my json is an array of objects:

[{ "code": "USD", "name": "United States Dollar" },
 { "code": "GBP", "name": "United Kingdom Pound" }...]

I want the default menu item to be the first item (USD). I have tried setting the ng-model to mob.currencyType and setting this in the controller both like:

  _this.currencyType = _this.currencyTypes[0];

and

_this.currencyType = { "code": "USD", "name": "United States Dollar" }

Neither approach gives me a default value set. What am I missing?

UPDATE

After some good suggestions from other users, and some experimenting, it would seem the problem was my data service call was not returning a promise:

  _this.currencyTypes = MockDataFactory.query({ filename: 'currency_codes' });

So I added

 _this.currencyTypes.$promise.then(function () {
    init();
  });

And then

  function init () {
    _this.currencyType = _this.currencyTypes[0];
  }

Answer 1

You can set using ng-init

<select ng-model="currency" ng-init="currency='United States Dollar'"   ng-options="code.name as code.name for code in currencyTypes">
</select>

DEMO

Answer 2

What you have is fine, just include a track by:

<select name="userCurrencyType" 
ng-model="mob.currencyType" 
ng-options="s.name + ' - ' + s.code for s in mob.currencyTypes track by s.code"></select>