Backbone.js Model defaults and parse -

i've got backbone.model representing google books api volume:

    var book = backbone.model.extend({      defaults: {         volumeinfo : {             title: 'n.a.',             authors: 'n.a.',             publisher: 'n.a.',             publisheddate: 'n.a.',             imagelinks : {                 smallthumbnail: '/unavailable.jpg'             }         }     },      parse: function(resp) {         if (resp.volumeinfo.authors) {             resp.volumeinfo.authors = resp.volumeinfo.authors.join(',');         }         return resp;     } }); 

which fed template:

<script type="text/template" id="bookcollectionrow">     <tr>         <td><img class="thumbnail" src="<%= volumeinfo.imagelinks.smallthumbnail %>" /></td>         <td><a target="_blank" href="<%= volumeinfo.canonicalvolumelink %>"><%= volumeinfo.title %></a></td>         <td><%= volumeinfo.authors %></td>         <td><%= volumeinfo.publisher %></td>         <td><%= volumeinfo.publisheddate %></td>     </tr> </script> 

upon parsing template, when volume json not contain imagelinks receive error:

uncaught typeerror: cannot read property 'smallthumbnail' of undefined. 

i know fix checking if in model or in template what's purpose of defaults model property then? work if not overriding parse?

a few things. first, shouldn't have nested objects backbone model attributes in general - can ok if can treat attribute atomically, perfect example of when can't. data-model perspective, imagelinks should own backbone model class, should volumeinfo.

second, if defaults object literal ({}) instead of function, same object used default attrs each model instance. think want this:

defaults: function(){     return {         volumeinfo : {} // should new volumeinfo({}) imo     }; }, 

but data model bigger issue - .defaults doesn't kind of nested-object-template thing seem going for, , reason: doesn't work well, first of many gotchas you'll run if don't keep instance data pretty flat.