AngularJs中的类操作和实例操作有什么区别？

Question

来自文档:

类操作返回空实例(下面有其他属性).实例操作返回操作的承诺

但是,文档没有明确区分类操作和实例操作.如果可能的话,你能指出一个很好的例子吗？

Answer 1

创建新资源类型时,可以为其提供可执行的操作列表.默认情况下,这些都是get,save,query,delete,和remove(我想删除只是删除别名).您可以添加自己的,如文档中所述.

关于类vs实例的事情是关于它为了方便使用而做的事情."类操作"是指从您自己创建的资源类调用操作,有点像其他语言中的静态或共享方法.当您还没有实例时,这可用作获取,查询或保存资源实例的入口点.get并且query是最明显的例子.如果您有Car资源,并且需要检索它,那么您从哪里开始？当然,有集体诉讼,如get.

现在,当您的资源类检索现有实例或创建新实例时,$resource将使用为您的资源定义的操作扩展您的实例,但为它们添加前缀,$以便它们不会与您资源上的字段发生冲突.这些是您的实例操作.实例和类之间的区别是实例是在当前实例的上下文中完成的.所以,如果你get的实例,但随后调用$save还是$delete该实例,它会保存或删除明确该实例.实例操作只是为了方便起见.

所以它们几乎相同,不同之处在于它们的使用环境.

function($resource) {     

   // first let's define a new resource for car, where all cars have an id field
   // calling $resource will create a new resource class that can be used to 
   // create, retrieve, update, or delete instances
   // this is usually done as a service and injected into controllers as needed.
   var Car = $resource('/api/car/:id', {id: '@id'});

   // the car class we just created has some class actions that can help you query for or get car instances
   // let's create a new instance of a car and save it
   var newCar = new Car({make: 'Toyota', model: 'Prius'});
   // the prototype of Car includes the instance action versions of the actions defined for the resource. below, $save is your instance action
   newCar.$save(); // server will respond with the object after it's saved, so we can now access the id. let's say the id it returned is 24, we'll reference this value later.


   // now, let's imagine some time later we want to retrieve the car and update it
   // Car.get is a class action that requests the resource from the server, parses the JSON into an object, and merges it with the Car instance prototype so you have your instance actions
   // let's get the car we created previously.
   // remember, this is done asynchronously, so we will do our work in a success handler that we provide to get
   Car.get({id: 24}, function(myCar) {
       // let's update the car now that we have it. let's set the year of the model and the color
       myCar.year = 2004;
       myCar.color = 'white';

       // now, let's save our changes by calling the instance action $save
       myCar.$save();
   });


   // now, let's query for all cars and get an array back
   // query is a class function that expects an array of your resource to be returned
   Car.query(function(cars) {
        // trivial example, we're just going to enumerate the cars we found and log some info about them
       for(var i = 0; i < cars.length; i++)
          console.log('Found ' + cars[0].color + ' ' cars[0].year + ' ' + cars[0].make + ' ' + cars[0].model);
   });


   // ok, let's delete the car we created earlier. use the class action delete
   Car.delete({id: 24});
}

从技术上讲,您可以将任何操作调用为类或实例,但很明显,有些操作很难用作实例操作,反之亦然.例如,虽然你在技术上可以query用作实例动作,但你不会在实践中这样做,因为它是额外的工作而且很尴尬(你必须这样做new Car().$query().这很愚蠢.Car.query()更容易,更有意义).因此,上面示例中的用法表示您的正常用法.

更新:

save VS $save

$save类似于save,但它假设您要在保存期间提交的数据本身,因为它$save是一个实例操作.它特别有用,因为在收到响应后,它将使用HTTP端点返回的对象更新自身.因此,如果您的服务使用服务器端填充的某些其他值(例如ID)保存对象,然后将对象作为JSON发回,$save则将使用返回的JSON对象更新实例.

 var car = new Car({make: 'Toyota', model: 'Prius'});
 // at this point there is no id property, only make and model
 car.$save(function() {
    // angular is async, so we need a success handler to continue the explanation

    // assuming your server assigned an ID and sent the resulting object back as JSON, you can now access id off the original object
    console.log(car.id); // has a value now
 });

您可以使用类方法执行类似的操作,但它很笨拙,特别是如果您正在处理它时控制器中的其他代码需要引用汽车

 Car.save({make: 'Toyota', model: 'Prius'}, function(car) {
       // ok, we have an ID now
       console.log(car.id);
 });

要么

 var car = new Car({...});
 Car.save(car, function(newCar) {
      car = newCar; // wut? that's awkward
 });

save 在您快速保存小对象或执行某种"火灾和忘记"的情况下,它可能很有用.无论如何,我很少使用save自己.