nl_tokens: serializeBelongsTo can be used to customize how DS . belongsTo properties are serialized .
pl_tokens: function ( record , json , relationship ) { var key = relationship . key ; var belongsTo = get ( record , key ) ; key = this . keyForRelationship ? this . keyForRelationship ( key , "belongsTo" ) : key ; if ( isNone ( belongsTo ) ) { json [ <mask> ] = belongsTo ; } else { json [ key ] = get ( belongsTo , 'id' ) ; } if ( relationship . options . polymorphic ) { this . serializePolymorphicType ( record , json , relationship ) ; } }