class Contractor extends Eloquent {
   protected $table = 'contractors';

   public function contractorTrades() {
          return $this->hasMany('ContractorTrade', 'contractor_id', 'id');
   }
}

class ContractorTrade extends Eloquent {
   protected $table = 'contractor_trades';

   public function contractor() {
          return $this->belongsTo('Contractor');
   }
}

class Trade extends Eloquent {
   protected $table = 'trades';
}

Contractor::first()->contractorTrades();