How do I union/merge two Collections by their '

问题:

I have two collections (Menu and Orders)

Menu collection contains array of Item objects

[{'id': '1', 'name': 'apple'}, {'id': '2', 'name': 'orange'}]

And Orders collection also contains array of Item objects

[{'id': '1', 'quantity': '0'}]

And I want them merged together their attributes by ID into another collection (this is needed for templating purposes only):

[{'id': '1', 'name': 'apple', 'quantity': '1'}, {'id': '2', 'name': 'orange'}]

Is there a underscore method on this or I need to define a function for this? [it seems i tried all merging functions on underscore but none of them works the way I expected]

回答1:

Assuming your collections are Backbone collections

var menus = new Backbone.Collection([
    {'id': '1', 'name': 'apple'}, 
    {'id': '2', 'name': 'orange'}
]);

var orders = new Backbone.Collection([{'id': '1', 'quantity': 1}]);

you can take advantage of the functions proxied on collections and of collection.get :

var merged = menus.map(function(menu) {
    var id = menu.get('id'),
        order = orders.get(id);

    if (!order) return menu.toJSON();

    return _.extend(menu.toJSON(), order.toJSON());
});

And a Fiddle to play with http://jsfiddle.net/bs6jN/

回答2:

Don't think there is a function defined in underscore.js for this but one way to do it is by using the _.map and _.find functions as follows,

var menus = [{'id': '1', 'name': 'apple'}, {'id': '2', 'name': 'orange'}];

var orders = [{'id': '1', 'quantity': '0'}];

var newMenu = _.map(menus, function (menu) {  
    var order = _.find(orders, function (o) { 
        return o.id == menu.id;
    }); 
    return _.extend(menu, order); 
});

console.log(newMenu);

回答3:

This should do the job:

var result = [];
_.each(menu, function(el){
    _.extend(el,_.where(orders, {id: el.id})[0] || {});
    result.push(el);
});

回答4:

If it is an union you want to do, you can do it using the underscore way:

// collectionUnion(*arrays, iteratee)
function collectionUnion() {
    var args = Array.prototype.slice.call(arguments);
    var it = args.pop();

    return _.uniq(_.flatten(args, true), it);
}

It just an improvment of the original function _.union(*arrays), adding an iteratee to work collection (array of object).

Here how to use it:

var result = collectionUnion(a, b, c, function (item) {
    return item.id;
});

The original function which is just working with array, looks like that:

_.union = function() {
  return _.uniq(flatten(arguments, true, true));
};

And in bonus a full example:

// collectionUnion(*arrays, iteratee)
function collectionUnion() {
    var args = Array.prototype.slice.call(arguments);
    var it = args.pop();

    return _.uniq(_.flatten(args, true), it);
}

var a = [{id: 0}, {id: 1}, {id: 2}];
var b = [{id: 2}, {id: 3}];
var c = [{id: 0}, {id: 1}, {id: 2}];

var result = collectionUnion(a, b, c, function (item) {
    return item.id;
});

console.log(result); // [ { id: 0 }, { id: 1 }, { id: 2 }, { id: 3 } ]

EDIT: I wrote a blog post if you want more details: http://geekcoder.org/union-of-two-collections-using-underscorejs/

回答5:

We ca merge with plain js like this

    var arrOne = [{'id': '1', 'name': 'apple'}, {'id': '2', 'name': 'orange'}];
    var arrTwo = [{'id': '1','quantity': '0'}];

    function mergeArr(arrOne, arrTwo) {
        var mergedArr = [];
        arrOne.forEach(function (item) {
            var O = item;
            arrTwo.forEach(function (itemTwo) {
                if (O.id === itemTwo.id) {
                    O.quantity = itemTwo.quantity;

                }
            });
            mergedArr.push(O);

        });

        return mergedArr;
    }