record.js

// ...

  /**
    A list of any attributes that are expected to be empty when the record
    is initially loaded.

    This property is very useful for working with partially loaded records in
    order to efficiently bring in the full data only when necessary.

    # What is a partially loaded record?

    Backend developers will often combine data in order to reduce the number
    of requests that an application has to make.  Remember that we should think
    of the backend as returning resources, not records.  And so a resource
    response may include data for several other related records.

    For example, say we want to show a details page for a Super Hero record
    including a list of their arch-enemies.  If each model was its own resource,
    we would have to get the entire hero record (ex. /heros/1) and then retrieve
    each of the entire arch-enemy records (ex. /villians/2, /villians/3, ...)
    just to show their names.  But if we only want the names of the villians
    right now, we could optimize the '/heros/:id' resource to also include some
    information of the related villians in order to only make one request for
    the page.

    When we retrieve the hero, we would load several MyApp.Villian records with
    the partial information we have so far.

    # Bringing in the missing data

    The problem becomes knowing when to bring in the full details for the
    partially loaded record.  We shouldn't just call refresh every time that
    the record will be displayed, because it may have already been fully
    loaded elsewhere and this would be wasteful.  Likewise, we don't want to
    use flags in our data handling code, because this is error-prone and it's
    easy to accidentally mark a record as dirty when trying to set flags on
    it.

    Instead, you can simply indicate the names of any attributes using
    sparseAttributes that, when requested, should retrieve the full details of
    the record.

    For example,

        MyApp.Villian = SC.Record.extend({

          aliases: SC.Record.attr(Array),

          birthdate: SC.Record.attr(SC.DateTime),

          henchmen: SC.Record.toMany('MyApp.Henchman'),

          name: SC.Record.attr(String),

          plotDevice: SC.Record.attr(String),

          // Getting any of these attributes will refresh the record if they
          // have not yet been loaded.
          sparseAttributes: ['birthdate', 'plotDevice']

        });

    Note, you don't have to list every attribute that may not be loaded upfront,
    just so long as at least one of the attributes is undefined initially and
    the record has never been retrieved.

    @type Array
    @default null
  */
  sparseAttributes: null,
  
// ...