Retrieve a particular item from an array of JSON objects

Question

Retrieve a particular item from an array of JSON objects

My services.js file is structured like this:

    var app = angular.module('starter.services', [])


    .factory('Studies',function($http,$filter){
        var studies = [];
        $http.get("studies.json").success(
                function(data){
                    //studies = data;
                    angular.copy(data, studies);
                }
            );
        single_object = $filter('filter')(studies, function (d) {return d.nodeRef === "56e3382b-9a76-48ee-9c14-907e71b7a184";})[0];
        console.log(single_object);
      return {
        all: function(){
          return studies;
        }
    };
    })

Within the code above, I am making a get request for a json file that contains objects with attributes, one of them being "nodeRef". My goal is to filter out a specific object based on its nodeRef match. However, when checking the console, it returns "undefined". This may be happening because the console log gets called before the json file is fully loaded. Can someone please help provide a solution?

javascript json angularjs angularjs-scope angular-filters

Answer 1

Answer №1

When making an asynchronous request and triggering the filter before receiving a response from the server, you may encounter undefined since you are trying to apply a filter to an empty array at that moment.

To resolve this issue, it is recommended to move your filter function call inside the success block for proper functioning:

Let's update the Angular module 'starter.services' with the necessary changes:

.factory('Studies',function($http,$filter){
    var studies = [];
    $http.get("studies.json").success(
            function(data){
                //studies = data;
                angular.copy(data, studies);
                single_result = filter("56e3382b-9a76-48ee-9c14-907e71b7a184");
                console.log(single_result);
            }
        );
  function filter(node) {
    if (studies.length > 0) {
      return $filter('filter')(studies, function (d) {return d.nodeRef === node;})[0];
    }
  }
  return {
    all: function(){
      return studies;
    },
    filtered: filter
};
})

Answer 2

When making an asynchronous request and triggering the filter before receiving a response from the server, you may encounter undefined since you are trying to apply a filter to an empty array at that moment.

To resolve this issue, it is recommended to move your filter function call inside the success block for proper functioning:

Let's update the Angular module 'starter.services' with the necessary changes:

.factory('Studies',function($http,$filter){
    var studies = [];
    $http.get("studies.json").success(
            function(data){
                //studies = data;
                angular.copy(data, studies);
                single_result = filter("56e3382b-9a76-48ee-9c14-907e71b7a184");
                console.log(single_result);
            }
        );
  function filter(node) {
    if (studies.length > 0) {
      return $filter('filter')(studies, function (d) {return d.nodeRef === node;})[0];
    }
  }
  return {
    all: function(){
      return studies;
    },
    filtered: filter
};
})

Answer 3

Answer №2

The console is displaying "undefined" because the studies variable has not yet been populated after the ajax request. To fix this, move the filter and console log inside the .success function:

$http.get("studies.json").success(
            function(data){
                //studies = data;
                angular.copy(data, studies);
                single_object = $filter('filter')(studies, function (d)  {return d.nodeRef === "56e3382b-9a76-48ee-9c14-907e71b7a184";})[0];
                console.log(single_object);
            }
        );

It may also be helpful to use a promise to update studies when it is fully loaded. You can learn more about promises in Angular using Angular $q

To implement a promise, return it and then resolve it within the $http.success function like so: var deferred = $q.defer(); .factory('Studies',function($http,$q,$filter){

    var studies = [];
    $http.get("studies.json").success(
            function(data){
                //studies = data;
                angular.copy(data, studies);
                
                deferred.resolve(studies);
            }
        );

  return {
    all: function(){
      return deferred.promise;
    }
};
//In your controller, or elsewhere...
Studies.all().then(function(studies){ 
$scope.studies = $filter('filter')(studies, function (d) {return d.nodeRef === "56e3382b-9a76-48ee-9c14-907e71b7a184";})[0];
})

Answer 4

The console is displaying "undefined" because the studies variable has not yet been populated after the ajax request. To fix this, move the filter and console log inside the .success function:

$http.get("studies.json").success(
            function(data){
                //studies = data;
                angular.copy(data, studies);
                single_object = $filter('filter')(studies, function (d)  {return d.nodeRef === "56e3382b-9a76-48ee-9c14-907e71b7a184";})[0];
                console.log(single_object);
            }
        );

It may also be helpful to use a promise to update studies when it is fully loaded. You can learn more about promises in Angular using Angular $q

To implement a promise, return it and then resolve it within the $http.success function like so: var deferred = $q.defer(); .factory('Studies',function($http,$q,$filter){

    var studies = [];
    $http.get("studies.json").success(
            function(data){
                //studies = data;
                angular.copy(data, studies);
                
                deferred.resolve(studies);
            }
        );

  return {
    all: function(){
      return deferred.promise;
    }
};
//In your controller, or elsewhere...
Studies.all().then(function(studies){ 
$scope.studies = $filter('filter')(studies, function (d) {return d.nodeRef === "56e3382b-9a76-48ee-9c14-907e71b7a184";})[0];
})

Retrieve a particular item from an array of JSON objects

Answer №1

Answer №2

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