10. Identity Map
Suspect:1 Roger
Suspect:2 Todd
Suspect:3 Michael
Suspect:4 Fred
... ...
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11. Object Creation
if class and ID is in identity map
return the cached object
else
create new object
put it in identity map
return the new object
end
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12. Backbone.IdentityMap
Backbone ‘Plugin’
Overrides Model Constructor
Does not alter original Backbone
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13. Before
...
var Suspect = Backbone.Model.extend({
...
});
var Suspects = Backbone.Collection.extend({
model: Suspect,
url: "/suspects"
});
...
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14. After
...
var Suspect = Backbone.IdentityMap(
Backbone.Model.extend({
...
})
);
var Suspects = Backbone.Collection.extend({
model: Suspect,
url: "/suspects"
});
...
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16. How does it work?
Backbone.IdentityMap = function(originalConstructor) {
var newConstructor =
_.extend(function(attributes, options) {
// Execute our identity map logic
...
return newOrCachedObject;
}, originalConstructor);
return newConstructor;
};
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17. How does it work
with Backbone?
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18. Backbone.Collection
...
_prepareModel: function(model, options) {
options || (options = {});
if (!(model instanceof Model)) {
var attrs = model;
options.collection = this;
model = new this.model(attrs, options);
if (!model._validate(model.attributes, options)) {
model = false;
}
} else if (!model.collection) {
model.collection = this;
}
return model;
},
...
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19. Backbone.Model
...
// Create a new model with identical attributes
to this one.
clone: function() {
return new this.constructor(this.attributes);
},
...
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20. Caveats
Maps take space
Logout should clear the map
Tests should clear the map
Can’t subclass (yet)
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