How AngularJS implements Model caching_AngularJS

How to implement a Model cache in AngularJS?

You can return a constructor in the Provider and design a cache field in the constructor. This approach will be introduced at the end of this article.

Generally speaking, Model should be assigned to a variable in Scope.

Some directly assign the object to the Scope variable; some return an object in the Provider and then assign it to the Scope variable; some return a constructor in the Provider and then assign it to the Scope variable. Let’s experience it one by one in this article.

First customize a directive to change the value of a scope variable by clicking a button.

angular
 .module('app',[])
 .directive('updater', function(){
  reutrn {
   scope: {
    user: '='
   },
   template: '<button>Change User.data to whaaaat&#63;</button>',
   link: function(scope, element, attrs){
    element.on('click', function(){
     scope.user.data = 'whaaaat&#63;';
     scope.$apply();
    })
   }
  }

■ Assign an object to the Scope variable

 .controller('FirstCtrl', function(){
  var first = this;
  first.user = {data: 'cool'};
 })
 .controller('SecondCtrl', function(){
  var second = this;
  second.user = {data: 'cool'};
 })

In page:

<div ng-controller="FirstCtrl">
 {{user.data}}
 <input ng-model="user.data">
 <div updater user="user"></div>
</div>

<div ng-controller="SecondCtrl">
 {{user.data}}
 <input ng-model="user.data">
 <div updater user="user"></div>
</div>

Above,

• ● Changing the value of input in FirstCtrl only affects the variable user in FirstCtrl and does not affect the variable user in SecondCtrl
• ● Clicking the button in FirstCtrl only affects the variable user in FirstCtrl
• ● Changing the value of input in SecondCtrl only affects the variable user in SecondCtrl and does not affect the variable user in FirstCtrl
• ● Clicking the button in SecondCtrl only affects the variable user in SecondCtrl

■ Return an object in Provider and assign it to Scope variable

 .controller('ThirdCtrl',['User', function(User){
  var third = this;
  third.user = User;
 }])
 .controller('FourthCtrl', ['User',function(User){
  var fourth = this;
  fourth.user = User;
 }])
 //provider返回对象
 .provider('User', function(){
  this.$get = function(){
   return {
    data: 'cool'
   }
  };
 })

In page:

<div ng-controller="ThirdCtrl">
 {{user.data}}
 <input ng-model="user.data">
 <div updater user="user"></div>
</div>

<div ng-controller="FourthCtrl">
 {{user.data}}
 <input ng-model="user.data">
 <div updater user="user"></div>
</div>

Above,

• ● Change the value of input in ThirdCtrl, and simultaneously affect the variables user in ThirdCtrl and FourthCtrl
• ● Click the button in ThirdCtrl to affect the variables user in ThirdCtrl and FourthCtrl simultaneously
• ● Change the value of input in FourthCtrl, and simultaneously affect the variables user in ThirdCtrl and FourthCtrl
• ● Click the button in FourthCtrl to simultaneously affect the variables user in ThirdCtrl and FourthCtrl

■ Return a constructor in Provider and assign it to the Scope variable

 .controller('FifthCtrl',['UserModel', function(UserModel){
  var fifth = this;
  fifth.user = new UserModel();
 }])
 .controller('SixthCtrl',['UserModel', function(UserModel){
  var sixth = this;
  sixth.user = new UserModel();
 }])
 //provider返回构造函数，每一次构造，就生成一个实例
 .provider('UserModel', function(){
  this.$get = function(){
   return function(){
    this.data = 'cool';
   }
  }
 })

In page:

<div ng-controller="FifthCtrl">
 {{user.data}}
 <input ng-model="user.data">
 <div updater user="user"></div>
</div>

<div ng-controller="SixthCtrl">
 {{user.data}}
 <input ng-model="user.data">
 <div updater user="user"></div>
</div>

Above,

• ● Changing the value of input in FifthCtrl only affects the variable user in FifthCtrl and does not affect the variable user in SixthCtrl
  
• ● Clicking the button in FifthCtrl only affects the variable user in FifthCtrl
  
• ● Changing the value of input in SixthCtrl only affects the variable user in SixthCtrl and does not affect the variable user in FifthCtrl
  
• ● Clicking the button in SixthCtrl only affects the variable user in SixthCtrl

■ Return a constructor in Provider with a cache field and assign it to the Scope variable

 .controller('SeventhCtrl',['SmartUserModel', function(SmartUserModel){
  var seventh = this;
  seventh.user = new SmartUserModel(1);
 }])
 .controller('EighthCtrl',['SmartUserModel', function(SmartUserModel){
  var eighth = this;
  eighth.user = new SmartUserModel(1);
 }])
 //provider返回构造函数，根据id获取，如果第一次就创建一个放缓存字段中，以后从缓存中获取
 .provider('SmartUserModel', function(){
  this.$get = ['$timeout', function($timeout){
   var User = function User(id){
    //先从缓存字段提取
    if(User.cached[id]){
     return User.cached[id];
    }
    this.data = 'cool';
    User.cached[id] = this;
   };
   
   User.cached = {};
   return User;
  }];
 })

In page:

<div ng-controller="SeventhCtrl">
 {{user.data}}
 <input ng-model="user.data">
 <div updater user="user"></div>
</div>

<div ng-controller="EighthCtrl">
 {{user.data}}
 <input ng-model="user.data">
 <div updater user="user"></div>
</div>

Above,

• ● Change the value of input in SeventhCtrl, and simultaneously affect the variables user in SeventhCtrl and EighthCtrl
• ● Click the button in SeventhCtrl to affect the variables user in SeventhCtrl and EighthCtrl simultaneously
• ● Change the value of input in EighthCtrl, and simultaneously affect the variables user in SeventhCtrl and EighthCtrl
• ● Click the button in EighthCtrl to affect the variables user in SeventhCtrl and EighthCtrl simultaneously

The above is the entire content of this article, I hope it will be helpful to everyone’s study.