Backbone.js Underscore.js filtering a collection v

问题:

I'm basically trying to do what is done with this question, but with an array and return all objects using the values of the corresponding array, not just the value: Filter backbone collection by attribute value

My natural instinct is to use _.filter or _.partition on the persons collection, but am confused on how these are being compared & returned and am not getting the desired outcome.

With the following, passing the id in via the router:

friendsRoute: function(id){                                                                       
  persons = new App.Collections.Persons();                                                   
  persons.fetch().done(function(){                                                           
    var single = persons.find(function(i){                                                   
      return i.get('id') == id;                                                              
    });                                                                                      
    var friendsIds = single.get('friends');


    var friends = ?


    //var friendsList = new App.Views.FriendsList();
    //friendsList.render({ friends: friends });
  });                                                                                        
},                                                                                           

I have a friendsIds array (Joe's friends):

friendsIds = [1,4,5]

And trying to get the matched ids from the following JSON and display their names in my friendsList view:

[
  { "id": 1, "name": "Steve", "age": 22, "friends": [4] },
  { "id": 2, "name": "Mary", "age": 18, "friends": [1,3] },
  { "id": 3, "name": "Joe", "age": 43, "friends": [1,4,5] },
  { "id": 4, "name": "Tommy", "age": 19, "friends": [1] },
  { "id": 5, "name": "Leslie", "age": 27, "friends": [2,4] }
]

回答1:

I think you could use a combination of map and findWhere to do this:

var friends = _.map(friendsIds, function(id) { 
    return _.findWhere(persons, { 'id': id }); 
});

回答2:

var friendsIds = [1,4,5];
var friends = [
  { "id": 1, "name": "Steve", "age": 22, "friends": [4] },
  { "id": 2, "name": "Mary", "age": 18, "friends": [1,3] },
  { "id": 3, "name": "Joe", "age": 43, "friends": [1,4,5] },
  { "id": 4, "name": "Tommy", "age": 19, "friends": [1] },
  { "id": 5, "name": "Leslie", "age": 27, "friends": [2,4] }
];
var filteredFriends = _.filter(friends, function(frnd){
return _.contains(friendsIds, frnd.id);
});
console.log(filteredFriends);

See the difference in performance with filter and map here

Make use of filter and contains

FIDDLE