Laravel의 leftJoin에서 폐쇄를 사용하면 여러 조건을 지정할 수 있습니다

-- 家族の情報を全て取得、５歳以下の子供がいればその情報も一緒に
SELECT * FROM families
  INNER JOIN persons 
    ON families.id = persons.family_id
    AND persons.age <= 5;

Family::leftJoin('persons', 'families.id', '=', 'persons.family_id')->get();

Family::leftJoin('persons', function ($join) {
    $join->on('families.id', '=', 'persons.family_id')
      ->where('persons.age', '<=', 5)
    })->get();

    public function join($table, $first, $operator = null, $second = null, $type = 'inner', $where = false)
    {
        $join = $this->newJoinClause($this, $type, $table);

        if ($first instanceof Closure) {
            $first($join);

            $this->joins[] = $join;

            $this->addBinding($join->getBindings(), 'join');
        }

        else {
            $method = $where ? 'where' : 'on';

            $this->joins[] = $join->$method($first, $operator, $second);

            $this->addBinding($join->getBindings(), 'join');
        }

        return $this;
    }