Another way in which several of the Underscore methods can be used is by extracting a specific Model or Models from a Collection. The simplest way to do this is with the where and findWhere methods, which return all the (or in the case of findWhere, the first) Models that match a provided attributes object. For example, if you want to extract all the books in a Collection, which have exactly one hundred pages, you can use the where method, as shown here:
var books = new Backbone.Collection([
{
pages: 100, title: "Backbone Essentials 5: The Essentials Return"
}, {
pages: 100, title: "Backbone Essentials 6: We're Not Done Yet?"
},{
pages: 25, title: "Completely Fake Title"
}
]);
var hundredPageBooks = books.where({pages: 100});
// hundredPageBooks array of all of the books except Completely Fake Title
var firstHundredPageBook = books.findWhere({pages: 100});
firstHundredPageBook; // Backbone Essentials 5: The Essentials ReturnWhat if we need a more complicated selection? For instance, what if instead of extracting all the books with exactly a hundred pages, we wanted to extract any book with a hundred or more pages? For this sort of extraction, we can use the more powerful filter method, or its inverse, the reject method, instead:
var books = new Backbone.Collection([
{
pages: 100, title: "Backbone Essentials 5: The Essentials Return"
}, {
pages: 200, title: "Backbone Essentials 7: How Are We Not Done Yet?"
}, {
pages: 25, title: "Completely Fake Title"
}
]);
var hundredPageOrMoreBooks = books.filter(function(book) {
return book.get('pages') >= 100;
});
hundredPageOrMoreBooks; // again, this will be an array of all books but the last
var hundredPageOrMoreBooks = books.reject(function(book) {
return book.get('pages') < 100;
});
hundredPageOrMoreBooks; // this will still be an array of all books but the last