Backbone Paginated Collection

backbonepaginatedcollection.js

/** 
   * A useful little pagination collection extension. Handles two
   * types of collections:
   *   1. Those where the number of pages is discoered on first page
   *   2. Those whose number of pages is known in advance.
   * Used by startup Collection and Trends collection.
   */
  ST.Collections.PaginatedCollection = Backbone.Collection.extend({

    initialize : function(attributes, options) {
      options = (options || {});
      
      options.page  = options.page || 1;
      options.pages = options.pages || 1;
      options.total_pages = options.pages;
      
      // If fetching total page number from data, what's the attribute
      // name
      options.pages_attribute = options.pages_attribute || null;
      
      // max number of pages we'll fetch. Null will fetch all.
      options.page_max = options.page_max || null;
      
      // by default append to collection
      options.append = options.append || true;

      _.extend(this, options);
    },

    clear : function() {

      // remove all models
      this.reset([], { silent : true });

      // reset page counts
      this.page = 1;
      this.pages = 1;
      
    }, 

    sync : function(method, model, options) {
      var type = methodMap[method];

      if (this.append) {
        options.add = true;
      }

      // Default JSON-request options.
      var params = _.extend({
        type:         type,
        dataType:     'json'
      }, options);

      // Ensure that we have a URL.
      if (!params.url) {
        params.url = model.url();
      }

      // Ensure that we have the appropriate request data.
      if (!params.data && model && (method == 'create' || method == 'update')) {
        params.contentType = 'application/json';
        params.data = JSON.stringify(model.toJSON());
      }

      // For older servers, emulate JSON by encoding the request into an HTML-form.
      if (Backbone.emulateJSON) {
        params.contentType = 'application/x-www-form-urlencoded';
        params.data        = params.data ? {model : params.data} : {};
      }

      // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
      // And an `X-HTTP-Method-Override` header.
      if (Backbone.emulateHTTP) {
        if (type === 'PUT' || type === 'DELETE') {
          if (Backbone.emulateJSON) {
            params.data._method = type;
          }
          params.type = 'POST';
          params.beforeSend = function(xhr) {
            xhr.setRequestHeader('X-HTTP-Method-Override', type);
          };
        }
      }

      // Don't process data on a non-GET request.
      if (params.type !== 'GET' && !Backbone.emulateJSON) {
        params.processData = false;
      }

      // make first request, then on success, make all subsequent requests
      var page_params = _.clone(params);
      var fetch_pages = function(start, end) {
        for (var i = start; i <= end; i++) {
          page_params.url = model.url(i);
          page_params.success = function(data) {
            model.page += 1;
            if (options.success) {
              options.success(data);
            }

            // if this is the last page, call the done callback if we have one
            if ((model.page - 1) == model.pages && options.done) {
              options.done(model);
            }

          };
          $.ajax(page_params);
        }
      };

      // do we know how many pages we are already fetching? If so
      // just make N simultanious requests.
      if (model.pages_attribute === null) {
        fetch_pages(model.page, model.pages);
      } else {
        // we are getting total number of pages from the first call
        // and then going to fetch everything

        var success = function(fetch_pages) {
          return function(data) {
            
            if (model.page === 1) {
              model.pages = Math.min(model.page_max, data[model.pages_attribute]);  
              model.total_pages = data[model.pages_attribute];
            }
            
            // process first page
            options.success(data);
            model.page += 1;

            // if this is the last page, call the done callback if we have one
            if ((model.page - 1) == model.pages && options.done) {
              options.done(model);
            }

            fetch_pages(model.page, model.pages);
          };
        }(fetch_pages);

        params.success = success;
        $.ajax(params);
      }
    }


  });