Fighting Ember-Data to get a related record from the store.

isNumericId.js

/*
  When traversing record.eachRelationship in Ember-Data you
  may want to actually look up and include the record if it 
  is already in the store.
  
  Unfortunately, when dealing with records that are being saved
  get(record,attribute) may or may not return the record even if
  it is in the store.
  
  If the ID were a temporary ember one (i.e. `<ember-234:null>`)
  then get typically results in the record being returned.
  
  BUT
  
  It may also return
  -a numeric id as an int
  -a numeric id, as a string
  -null as null
  -null as 'null'
  -an array
  
  get is Ember.get
  _store is a reference to the store passed in to the parent method
*/

//option 1: hasRecordForId
var lookupRecord = function(parent,relationship){

  //usually this will be an existing record
  var relatedRecord = get(parent,relationship.key),
      type = relationship.type.typeKey
      ;
                    
  if( !isNaN(Number(relatedRecord)) ) {

      //check that there is a record in the store
      if( _store.hasRecordForId(type, relatedRecord) ) {
          //grab the record
          relatedRecord = _store.recordForId(type,relatedRecord);
      }
  }

  return relatedRecord;
}

/*
  Option 1 is a shorthand for weeding out objects, arrays,
  and non numbery strings.
  
  You might think option 1 above would be solid (it isn't, string
  'null' IDs turn out to have all sorts of bizzare return behavior).
*/


//option 2: dirtiest simple test
var lookupRecord = function(parent,relationship){

  //usually this will be an existing record
  var relatedRecord = get(parent,relationship.key),
      type = relationship.type.typeKey
      ;
                    
  if( relatedRecord == parseInt(relatedRecord,10) ) {

      //check that there is a record in the store
      if( _store.hasRecordForId(type, relatedRecord) ) {
          //grab the record
          relatedRecord = _store.recordForId(type,relatedRecord);
      }
  }

  return relatedRecord;
}
/*
  Option 2 works and is the shortest test that passes all our tests.
  
  But it is difficult to see clearly why it works.  Option 2 works
  because when parseInt(val,10) is called on an array, object, or non
  number string it will return NaN, while for a numberish string it
  will return that string recast as an int.  int 1 == '1' because ==
  does not enforce type but instead recasts the types of the objects
  it is checking.  Understanding everything that is going on makes
  this difficult to maintain.
*/


//option 3: maintainably clear test
var lookupRecord = function(parent,relationship){

  //usually this will be an existing record
  var relatedRecord = get(parent,relationship.key),
      type = relationship.type.typeKey,
      isNumericId = function(id){
          return id !== null && id !== 'null' && !isNaN(Number(id));
      }
      ;
                    
  if( isNumericId(relatedRecord) ) {

      //check that there is a record in the store
      if( _store.hasRecordForId(type, relatedRecord) ) {
          //grab the record
          relatedRecord = _store.recordForId(type,relatedRecord);
      }
  }

  return relatedRecord;
}
/*
  Instead of relying on murky type conversion underneath, we separate
  out null and 'null' as individual tests, and use our shorthand for
  filtering out anything that isn't numberish for the rest.
*/