具有相同键的JSON数组的总和

Question

I have a problem with javascript objects with arrays trying to update "quantity" if the selected item is choosen again.

The object I use is defined like this:

var Cart = {
    User: 0,
    Store: 0,
    UserID: 0, 
    Deliver: "Entrega",
    Date: "2014-01-01",
    Total: 0,
    ProductsCart: []
};

And in ProductsCart the array Im creating is the following:

Cart.ProductsCart.push({
        "ProductID": id,    //value sent from javascript function 
        "Quantity": Number(Quantity),
        "Price": Price.toFixed(2),
        "Name": name,
        "Desc": desc,
        "Date": date,
        "StoreID": store,
        "UserID": Number(UserID) //Special

The problem Im facing right now is that I have a javascript code to update the quantity of a selected product again, if exist it update the quantity but sometimes it works and sometimes not. This is the code

  var temp = {},
            i;

        for (i = Cart.ProductsCart.length - 1; i >= 0; i -= 1) {
            ProductID = Cart.ProductsCart[i].ProductID;
            UserID = Cart.ProductsCart[i].NinoID;
            if (temp.hasOwnProperty(ProductID) && temp.hasOwnProperty(UserID)) {
                Cart.ProductsCart[temp[ProductID]].Quantity += Cart.ProductsCart[i].Quantity;
                //Splice to make one array with updated quantity?
                Cart.ProductsCart.splice(i, 1);
            } else {

                temp[ProductID] = i;
                //I need to identify one product per user and filter the productos by user so Im using that UserID to identify every array per user 
                temp[UserID] = UserID;
            }
        }
        console.log(Cart.ProductsCart);

Now the problem is that sometimes it add the specific quantity to the product like

• Pizza, Quantity 1
• Drink, Quantity 1

But for some reason for the same user or different user I try to add a Cake, Quantity 1 the pizza or the Drink is altered in its quantity and the cake doesnt exist anymore. Hope you can guide where its the problem Thanks in advance

EDIT-------------

The original script (mine) works with specific products, because doing some tests I found that Im using fullcalendar and on every click on a specific day the code doesnt work, but If i dont make a click the code works.

Other thing is that Im using AJAX to bring the products by categories, the problem is not getting the ID, the problem is they dont identify the existing array

Answer 1

Suppose your array looks like this:

Pizza  4
Cake   3
Pizza  2
Pizza  5
Drink  2

At i = 2, you merge the two Pizza lines and splice one of them out:

Pizza  4
Cake   3
Pizza  7
Drink  2

The problem is, now you Pizza line is at index 2, not 3, but you still have temp.Pizza = 3 . So, at i = 0, you will incorrectly merge into the Drink line, which is now at index 3.

One solution would be to go forward through the array when merging, instead of backward, and splice() the later repetitions of a product, leaving the first one at the index that you recorded. Then just make sure that you do i -= 1 after splicing so that you'll look at that index again now that some other item has moved into that index.

Answer 2

Your problem is you're splicing your array mid-loop, which will cause undesired effects. You are iterating over an array for every item in the array, yet you are changing the items in that array as you are iterating. Can you see how this would cause you problems? :)

Take this example, which you can see demoed on this jsfiddle .

var arr = [
    "one",
    "two",
    "three",
    "four",
    "five"    
];

console.log('Without Splice ...');

for ( var i = 0; i <= arr.length - 1; i++ ) {
    console.log(arr[i]);
}

console.log('With Splice ...');

for ( var i = 0; i <= arr.length - 1; i++ ) {
    console.log(arr[i]);
    arr.splice(i, 1);
}

The first iteration logs each item, as you'd expect. The second iteration, though, logs only every other item (one, three, five). A safer bet would be to keep track of the items you want to remove in a temporary array, and then when you're iteration is done remove the items from your source based on what's in the temporary array.

Answer 3

Sorry, but I'm just not following your structure.

What I would do is make it so that you have an array of Cart objects and each Cart object would have essential items like the user the cart belongs to and what items and what quantity of those items:

/**
* @constructor
*/
var Cart = function(){
    var userID;
    var items = [];
    // array of Item
    ...
};

/**
* method for checking if item exists in cart
*/
Cart.prototype.hasItem = function(item){
    for (var i = 0; i < this.items.length; i++){
        if (this.items[i].itemId === item.itemId){
            return true;
        }
    }
    return false;
}


/**
* method for checking if item exists in cart
*/
Cart.prototype.updateItemQty= function(item, difference){
    for (var i = 0; i < this.items.length; i++){
        if (this.items[i].itemId === item.itemId){
            this.items[i].qty += difference;
        }
    }
}

Define Item:

var Item = function() {
    var ItemId;
    var qty;
    ...
}

then keep an array of Cart

var carts = [];

now provide a method or function for adding items to a particular cart

function addItem(item, userId){
    for (var i = 0; i < carts.length; i++){
        if (carts[i].userId === userId){
            // add or update item
            if (carts[i].hasItem(item)){
                carts[i].updateItemQty(item, 1);
            } else {
                carts[i].addItem(item);
            }
        } else {
            // add a new cart to carts array first
            // then add the item to that new cart
        }
    }

}