combining multiple API requests and processing before returning promise from factory method

Question

combining multiple API requests and processing before returning promise from factory method

For quite some time, I've been relying on the promise generated by a simple http method. However, my current need involves chaining multiple API calls, processing the data, and then returning that processed data. The issue I'm encountering with my existing setup is that the factory isn't returning the promise, causing it to not wait for the data before moving on to the next line in the controller.

app.factory('mytestService', ['$http', function($http){
    getSomeDataById: function(id){
    var userAllProjects = [];
     var myHelperService = this.getSecondData;
     this.getFirstData(id).then(function(response){ // first api call
         var idObjectValue = response['result'][0]['id'];
         myHelperService(idObjectValue).then(function(response){ //second api call
           userAllProjects= response['projectList']
        });
   });
    return userAllProjects
   }
]);

Now, when attempting to access in the controller:

$scope.allProjects = mytestService.getSomeDataById(1234);
console.log($scope.allProjects);

the console displays undefined. It's clear that this happens because it doesn't wait for the service to complete before moving on to the next line.

I am new to Angular promises and would appreciate any guidance on how to address this issue. Feel free to ask if you require more details.

javascript angularjs promise

Answer 1

Answer №1

Presenting a new concept called Promise Chaining, which is generally favored over the creation of new deferred

fetchDataById: function(id){
    var userProjects = [];
	var helperService = this.retrieveAdditionalData;

    // Instead of creating a new promise, 
    // return the existing one to avoid unresolved promises if any call in the chain fails
    return this.fetchFirstData(id).then(function(response){ // initial API request
        var idValue = response['result'][0]['id'];
        return helperService(idValue);  // secondary API request
        // Avoid chaining .then here for better readability, 
        // it can be moved to the outer layer

    }).then(function(response){
        userProjects = response['projectList'];
        // Return necessary data for use in .then of fetchDataById() here
    });
});

Answer 2

Presenting a new concept called Promise Chaining, which is generally favored over the creation of new deferred

fetchDataById: function(id){
    var userProjects = [];
	var helperService = this.retrieveAdditionalData;

    // Instead of creating a new promise, 
    // return the existing one to avoid unresolved promises if any call in the chain fails
    return this.fetchFirstData(id).then(function(response){ // initial API request
        var idValue = response['result'][0]['id'];
        return helperService(idValue);  // secondary API request
        // Avoid chaining .then here for better readability, 
        // it can be moved to the outer layer

    }).then(function(response){
        userProjects = response['projectList'];
        // Return necessary data for use in .then of fetchDataById() here
    });
});

Answer 3

Answer №2

Instead of using then in your controller, you can integrate it within the controller itself.

Factory

app.factory('mytestService', ['$http', function($http) {
    getSomeDataById: function(id) {
        var myHelperService = this.getSecondData;
        return this.getFirstData(id);
    },
    secondApiCall : function(idObjectValue){
      return myHelperService(idObjectValue);
    }
}]);

Controller

mytestService.getSomeDataById(1234).then(function(response){
  mytestService.secondApiCall(response['result'][0]['id']).then(function(response2){
    $scope.allProjects = response.data;
  })
});

Answer 4

Instead of using then in your controller, you can integrate it within the controller itself.

Factory

app.factory('mytestService', ['$http', function($http) {
    getSomeDataById: function(id) {
        var myHelperService = this.getSecondData;
        return this.getFirstData(id);
    },
    secondApiCall : function(idObjectValue){
      return myHelperService(idObjectValue);
    }
}]);

Controller

mytestService.getSomeDataById(1234).then(function(response){
  mytestService.secondApiCall(response['result'][0]['id']).then(function(response2){
    $scope.allProjects = response.data;
  })
});

Answer 5

Answer №3

Check out the following code snippet.

fetchDataById: function(id){
  var userDataPromise = $q.defer();
  var myService = this.getSecondData;
  
  this.getFirstData(id).then(function(response){ // first API call
     var idValue = response['result'][0]['id'];
     
     myService(idValue).then(function(response){ //second API call
       userDataPromise.resolve(response['projectList']);
    });
  });
  
  return userDataPromise.promise;
}

The concept here is to create a deferred object initially and then return the promise. Once the data is retrieved, resolve the deferred object which will make the data available in your controller.

Please note that you must include $q as a dependency for this to work correctly.

Reference: https://docs.angularjs.org/api/ng/service/$q

Answer 6

Check out the following code snippet.

fetchDataById: function(id){
  var userDataPromise = $q.defer();
  var myService = this.getSecondData;
  
  this.getFirstData(id).then(function(response){ // first API call
     var idValue = response['result'][0]['id'];
     
     myService(idValue).then(function(response){ //second API call
       userDataPromise.resolve(response['projectList']);
    });
  });
  
  return userDataPromise.promise;
}

The concept here is to create a deferred object initially and then return the promise. Once the data is retrieved, resolve the deferred object which will make the data available in your controller.

Please note that you must include $q as a dependency for this to work correctly.

Reference: https://docs.angularjs.org/api/ng/service/$q

combining multiple API requests and processing before returning promise from factory method

Answer №1

Answer №2

Answer №3

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