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// A simple module to replace `Backbone.sync` with *localStorage*-based
// persistence. Models are given GUIDS, and saved into a JSON object. Simple
// as that.
// Generate four random hex digits.
function S4() {
return (((1+Math.random())*0x10000)|0).toString(16).substring(1);
};
// Generate a pseudo-GUID by concatenating random hexadecimal.
function guid() {
return (S4()+S4()+"-"+S4()+"-"+S4()+"-"+S4()+"-"+S4()+S4()+S4());
};
// Our Store is represented by a single JS object in *localStorage*. Create it
// with a meaningful name, like the name you'd give a table.
var Store = function(name) {
this.name = name;
var store = localStorage.getItem(this.name);
this.data = (store && JSON.parse(store)) || {};
};
_.extend(Store.prototype, {
// Save the current state of the **Store** to *localStorage*.
save: function() {
localStorage.setItem(this.name, JSON.stringify(this.data));
},
// Add a model, giving it a (hopefully)-unique GUID, if it doesn't already
// have an id of it's own.
create: function(model) {
if (!model.id) model.id = model.attributes.id = guid();
this.data[model.id] = model;
this.save();
return model;
},
// Update a model by replacing its copy in `this.data`.
update: function(model) {
this.data[model.id] = model;
this.save();
return model;
},
// Retrieve a model from `this.data` by id.
find: function(model) {
return this.data[model.id];
},
// Return the array of all models currently in storage.
findAll: function() {
return _.values(this.data);
},
// Delete a model from `this.data`, returning it.
destroy: function(model) {
delete this.data[model.id];
this.save();
return model;
}
});
// Override `Backbone.sync` to use delegate to the model or collection's
// *localStorage* property, which should be an instance of `Store`.
Backbone.sync = function(method, model, options) {
var resp;
var store = model.localStorage || model.collection.localStorage;
switch (method) {
case "read": resp = model.id ? store.find(model) : store.findAll(); break;
case "create": resp = store.create(model); break;
case "update": resp = store.update(model); break;
case "delete": resp = store.destroy(model); break;
}
if (resp) {
options.success(resp);
} else {
options.error("Record not found");
}
};
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