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rocksdb/include/leveldb/write_batch.h

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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
//
// WriteBatch holds a collection of updates to apply atomically to a DB.
//
// The updates are applied in the order in which they are added
// to the WriteBatch. For example, the value of "key" will be "v3"
// after the following batch is written:
//
// batch.Put("key", "v1");
// batch.Delete("key");
// batch.Put("key", "v2");
// batch.Put("key", "v3");
//
// Multiple threads can invoke const methods on a WriteBatch without
// external synchronization, but if any of the threads may call a
// non-const method, all threads accessing the same WriteBatch must use
// external synchronization.
#ifndef STORAGE_LEVELDB_INCLUDE_WRITE_BATCH_H_
#define STORAGE_LEVELDB_INCLUDE_WRITE_BATCH_H_
#include <string>
#include "leveldb/status.h"
namespace leveldb {
class Slice;
class WriteBatch {
public:
WriteBatch();
~WriteBatch();
// Store the mapping "key->value" in the database.
void Put(const Slice& key, const Slice& value);
// Merge "value" with the existing value of "key" in the database.
// "key->merge(existing, value)"
void Merge(const Slice& key, const Slice& value);
// If the database contains a mapping for "key", erase it. Else do nothing.
void Delete(const Slice& key);
// Clear all updates buffered in this batch.
void Clear();
// Support for iterating over the contents of a batch.
class Handler {
public:
virtual ~Handler();
virtual void Put(const Slice& key, const Slice& value) = 0;
// Merge is not pure virtual. Otherwise, we would break existing
// clients of Handler on a source code level.
// The default implementation simply throws a runtime exception.
virtual void Merge(const Slice& key, const Slice& value);
virtual void Delete(const Slice& key) = 0;
};
Status Iterate(Handler* handler) const;
// Retrieve the serialized version of this batch.
std::string Data() { return rep_; }
// Returns the number of updates in the batch
int Count() const;
// Constructor with a serialized string object
WriteBatch(std::string rep): rep_(rep) {}
private:
friend class WriteBatchInternal;
std::string rep_; // See comment in write_batch.cc for the format of rep_
// Intentionally copyable
};
} // namespace leveldb
#endif // STORAGE_LEVELDB_INCLUDE_WRITE_BATCH_H_