backbone.js - How to prevent adding same JSON object or model to collection multiple times? -

i json data via ajax, want add these data collection. want add/update new/existing objects collection. did in 2 ways. both not working, , kind of know why not working. there must solution that.
1)

var book = backbone.model.extend({}); var library = backbone.collection.extend({model: book}); var library = new library(); var bookjson = {   title: "one thousand , 1 nights",   author: "scheherazade" } var book1 = new book(bookjson); var book2 = new book(bookjson); library.add(book1, {merge: true}); library.add(book2, {merge: true}); 

result library.length = 2

2)

var book = backbone.model.extend({}); var library = backbone.collection.extend({model: book}); var library = new library(); var book = {   title: "one thousand , 1 nights",   author: "scheherazade" } library.add(book, {merge: true}); library.add(book, {merge: true}); 

result library.length = 2

i want add/update same model/json object once collection. thanks.

your json has no id value, backbone not know same when add twice.

var book = backbone.model.extend({}); var library = backbone.collection.extend({model: book}); var library = new library(); var book = {   id: 1,   // 'id' default idattribute.   title: "one thousand , 1 nights",   author: "scheherazade" } library.add(book, {merge: true}); library.add(book, {merge: true}); 

or:

var book = backbone.model.extend({     idattribute: 'title'  // might not thing use id, though. }); var library = backbone.collection.extend({model: book}); var library = new library(); var book = {   title: "one thousand , 1 nights",   author: "scheherazade" } library.add(book, {merge: true}); library.add(book, {merge: true}); 

normally, not set id on client side, let server assign id when first save new model. but... lack of id why see 2 code.