public:

explicit LevelDBCursor(leveldb::Iterator* iter)

: iter_(iter) { SeekToFirst(); }

~LevelDBCursor() { delete iter_; }

virtual void SeekToFirst() { iter_->SeekToFirst(); }

virtual void Next() { iter_->Next(); }

virtual string key() { return iter_->key().ToString(); }

virtual string value() { return iter_->value().ToString(); }

virtual bool valid() { return iter_->Valid(); }

private:

leveldb::Iterator* iter_;

public:

explicit LevelDBTransaction(leveldb::DB* db) : db_(db) { CHECK_NOTNULL(db_); }

virtual void Put(const string& key, const string& value) {

batch_.Put(key, value);

}

virtual void Commit() {

leveldb::Status status = db_->Write(leveldb::WriteOptions(), &batch_);

CHECK(status.ok()) << "Failed to write batch to leveldb "

<< std::endl << status.ToString();

}

private:

leveldb::DB* db_;

leveldb::WriteBatch batch_;

DISABLE_COPY_AND_ASSIGN(LevelDBTransaction);

public:

LevelDB() : db_(NULL) { }

virtual ~LevelDB() { Close(); }

virtual void Open(const string& source, Mode mode);

virtual void Close() {

if (db_ != NULL) {

delete db_;

db_ = NULL;

}

}

virtual LevelDBCursor* NewCursor() {

return new LevelDBCursor(db_->NewIterator(leveldb::ReadOptions()));

}

virtual LevelDBTransaction* NewTransaction() {

return new LevelDBTransaction(db_);

}

private:

leveldb::DB* db_;