[
  {
    "destination" : "incline_cal_by_user",
    "source"      : [ "incline_cal", "incline_cal_member" ],
    "pk_columns"  : {
      "incline_cal_member.user_id" : "_user_id",
      "incline_cal_member.cal_id"  : "_cal_id"
    },
    "npk_columns" : {
      "incline_cal.at_time" : "_at_time"
    },
    "merge"       : {
      "incline_cal.id" : "incline_cal_member.cal_id"
    },
    "shard-key"   : "_user_id"
  }
]