How to index and query STL map containers by multiple keys?

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悲哀的现实 2020-12-16 14:20

I came across one requirement where the record is stored as

Name :  Employee_Id  :  Address

where Name and Employee_Id are supposed to be k

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盖世英雄少女心 (楼主)

2020-12-16 15:09

Example with tew keys:

#include 
#include 
#include 

template 
class MultiKeyMap {
  public:
  struct Entry
  {
    KEY1 key1;
    KEY2 key2;
    OTHER otherVal;
    Entry( const KEY1 &_key1,
           const KEY2 &_key2,
           const OTHER &_otherVal):
           key1(_key1),key2(_key2),otherVal(_otherVal) {};
    Entry() {};
  };
  private:
  struct ExtendedEntry;
  typedef std::shared_ptr ExtendedEntrySptr;
  struct ExtendedEntry {
    Entry entry;
    typename std::map::iterator it1;
    typename std::map::iterator it2;
    ExtendedEntry() {};
    ExtendedEntry(const Entry &e):entry(e) {};
  };
  std::map byKey1;
  std::map byKey2;

  public:
  void del(ExtendedEntrySptr p)
  {
    if (p)
    {
      byKey1.erase(p->it1);
      byKey2.erase(p->it2);
    }
  }

  void insert(const Entry &entry) {
    auto p=ExtendedEntrySptr(new ExtendedEntry(entry));
    p->it1=byKey1.insert(std::make_pair(entry.key1,p)).first;
    p->it2=byKey2.insert(std::make_pair(entry.key2,p)).first;
  }
  std::pair getByKey1(const KEY1 &key1) 
  {
    const auto &ret=byKey1[key1];
    if (ret)
      return std::make_pair(ret->entry,true);
    return std::make_pair(Entry(),false);
  }
  std::pair getByKey2(const KEY2 &key2) 
  {
    const auto &ret=byKey2[key2];
    if (ret)
      return std::make_pair(ret->entry,true);
    return std::make_pair(Entry(),false);
  }
  void deleteByKey1(const KEY1 &key1)
  {
    del(byKey1[key1]);
  }
  void deleteByKey2(const KEY2 &key2)
  {
    del(byKey2[key2]);
  }
};


int main(int argc, const char *argv[])
{
  typedef MultiKeyMap M;
  M map1;
  map1.insert(M::Entry(1,"aaa",7));
  map1.insert(M::Entry(2,"bbb",8));
  map1.insert(M::Entry(3,"ccc",9));
  map1.insert(M::Entry(7,"eee",9));
  map1.insert(M::Entry(4,"ffffd",9));
  map1.deleteByKey1(7);
  auto a=map1.getByKey1(2);
  auto b=map1.getByKey2("ffffd");
  auto c=map1.getByKey1(7);
  std::cout << "by key1=2   (should be bbb ): "<< (a.second ? a.first.key2:"Null") << std::endl;
  std::cout << "by key2=ffffd (should be ffffd ): "<< (b.second ? b.first.key2:"Null") << std::endl;
  std::cout << "by key1=7   (does not exist): "<< (c.second ? c.first.key2:"Null") << std::endl;
  return 0;
}

Output:

by key1=2   (should be bbb ): bbb
by key2=ffffd (should be ffffd ): ffffd
by key1=7   (does not exist): Null

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