有没有性LevelDB的C＃的一个很好的端口？ [英] Is there a good port of leveldb for C#?
问题描述
我希望在我的纯C＃项目使用性LevelDB。
I wish to use leveldb in my pure C# project.
我用Google搜索了性LevelDB的C＃版本，但没有得到幸运的。
I have googled for a C# version of leveldb, but got no lucky.
任何人能告诉我在哪里可以找到性LevelDB的C＃版本？
Any one can tell me where I can find a C# version of leveldb?
感谢
推荐答案
不，我知道，但我一直在使用它在我的C＃项目中。如果你熟悉C ++，那么你就可以使自己的CLI的包装（不应该是一个比较麻烦），把它做成一个DLL，然后就可以加载像任何其他程序集引用C＃项目的DLL。
Not that I know of, but I've been using it in my C# project. If you're familiar with C++, then you can make your own CLI wrapper (shouldn't be that much trouble), build it as a DLL and then you can load that DLL in your C# project like any other assembly reference.
有一个窗户端口性LevelDB ，这是一个有点棘手得到它到Visual Studio，但如果你有问题我可以上传我的Visual Studio 2010的解决方案（这是战斗75％），整个事情的设置和准备建（除CLI包装）。我可以把它挂在github上或东西，这我其实在做反正规划，但我会尽快给你。
There is a windows port for leveldb and it's a little tricky to get it into Visual Studio, but if you're having trouble I can upload my Visual Studio 2010 solution (which is 75% of the battle) with the whole thing set-up and ready to build (except the CLI wrapper). I can put it up on github or something, which I'm actually planning on doing anyway, but I'll expedite it for you.
就像我说的，我一直在使用我的C＃项目的做法，它的伟大工程。不过，如果你有非常高的性能要求，那么我会建议，以减少配料上工作 p /调用。
Like I said, I've been using that approach for my C# project and it works great. However, if you have really high performance requirements, then I would recommend batching up "work" in order to reduce the P/Invokes.
请注意，我没有这个选项编译代码，但我只是张贴它作为一个例子。你的头文件可能是这样的：
Please note that I have not compiled this code, but I'm just posting it as an example. Your header file might look like this:
#pragma once
#include <exception>
#include "leveldb\db.h"
using namespace System::Runtime::InteropServices;
// Create the namespace
namespace LevelDBWrapperNS
{
// Note that size_t changes depending on the target platform of your build:
// for 32-bit builds, size_t is a 32-bit unsigned integer.
// for 64-bit builds, size_t is a 64-bit unsigned integer.
// There is no size_t equivalent in C#, but there are ways to
// mimic the same behavior. Alternately, you can change the
// size_t to unsigned long for 32-bit builds or unsigned long long (64-bit)
// Declare the leveldb wrapper
public ref class LevelDBWrapper
{
private:
leveldb::DB* _db;
public:
LevelDBWrapper(const std::string dataDirectory);
~LevelDBWrapper();
// A get method which given a key, puts data in the value array
// and sets the valueSize according to the size of the data it
// allocated. Note: you will have to deallocate the data in C#
void Get(const char* key, const size_t keySize, char* value, size_t &valueSize);
// A put method which takes in strings instead of char*
bool Put(const std::string key, const std::string value);
// A put method which takes in char* pointers
bool Put(const char* key, const size_t keySize, const char* value, const size_t valueSize);
// A delete method
bool Delete(const char* key, const size_t keySize);
private:
void Open(const char* dataDirectory);
};
}
您的cpp文件将是沿着线：
Your cpp file is going to be along the lines of:
#include "LevelDBWrapper.h"
// Use the same namespace as the header
namespace LevelDBWrapperNS
{
LevelDBWrapper::LevelDBWrapper(const std::string dataDirectory)
{
Open(dataDirectory.c_str());
}
LevelDBWrapper::~LevelDBWrapper()
{
if(_db!=NULL)
{
delete _db;
_db= NULL;
}
// NOTE: don't forget to delete the block cache too!!!
/*if(options.block_cache != NULL)
{
delete options.block_cache;
options.block_cache = NULL;
}*/
}
bool LevelDBWrapper::Put(const char* key, const size_t keySize, const char* value, const size_t valueSize)
{
leveldb::Slice sKey(key, keySize);
leveldb::Slice sValue(value, valueSize);
return _db->Put(leveldb::WriteOptions(), sKey, sValue).ok();
}
void LevelDBWrapper::Open(const char* dataDirectory)
{
leveldb::Options options;
// Create a database environment. This will enable caching between
// separate calls (and improve performance). This also enables
// the db_stat.exe command which allows cache tuning. Open
// transactional environment leveldb::Options options;
options.create_if_missing = true;
// Open the database if it exists
options.error_if_exists = false;
// 64 Mb read cache
options.block_cache = leveldb::NewLRUCache(64 * 1024 * 1024);
// Writes will be flushed every 32 Mb
options.write_buffer_size = 32 * 1024 * 1024;
// If you do a lot of bulk operations it may be good to increase the
// block size to a 64k block size. A power of 2 block size also
// also improves the compression rate when using Snappy.
options.block_size = 64 * 1024;
options.max_open_files = 500;
options.compression = leveldb::kNoCompression;
_db = NULL;
// Open the database
leveldb::Status status = leveldb::DB::Open(options, dataDirectory, &_db);
// Check if there was a failure
if(!status.ok())
{
// The database failed to open!
if(status.ToString().find("partial record without end")!=std::string::npos)
{
// Attempting to recover the database...
status = leveldb::RepairDB(dataDirectory, options);
if(status.ok())
{
// Successfully recovered the database! Attempting to reopen...
status = leveldb::DB::Open( options, dataDirectory, &_db);
}
else
{
// Failed to recover the database!
}
}
// Throw an exception if the failure was unrecoverable!
if(!status.ok())
{
throw std::runtime_error(std::string("Unable to open: ") + std::string(dataDirectory) +
std::string(" ") + status.ToString());
}
}
}
}
这。应该让你在正确的方向
This should get you in the right direction.
确定，得到的将是这样的：
OK, Get will look like this:
// Returns a buffer containing the data and sets the bufferLen.
// The user must specify the key and the length of the key so a slice
// can be constructed and sent to leveldb.
const unsigned char* Get(const char* key, const size_t keyLength, [Out]size_t %bufferLen);
来源是沿着线：
const unsigned char* LevelDBWrapper::Get(const char* key, const size_t keyLength, [Out]size_t %bufferLen)
{
unsigned char* buffer = NULL;
std::string value;
leveldb::Status s = db->Get(leveldb::ReadOptions(), Slice(key, keyLength), &value);
if(s.ok())
{
// we found the key, so set the buffer length
bufferLen = value.size();
// initialize the buffer
buffer = new unsigned char[bufferLen];
// set the buffer
memset(buffer, 0, bufferLen);
// copy the data
memcpy(memcpy((void*)(buffer), value.c_str(), bufferLen);
}
else
{
// The buffer length is 0 because a key was not found
bufferLen = 0;
}
return buffer;
}
请注意，不同的数据可能有不同的编码，所以我觉得通过非托管之间的数据的最安全的方式和托管代码使用指针和 UnmanagedMemoryStream 这里是你将如何获得在C＃中的一个关键相关的数据：
Note that different data may have different encoding, so I feel like the safest way to pass data between your unmanaged and managed code is to use pointers and an UnmanagedMemoryStream. Here is how you would get the data associated with a key in C#:
UInt32 bufferLen = 0;
byte* buffer = dbInstance.Get(key, keyLength, out bufferLen);
UnmanagedMemoryStream ums = new UnmanagedMemoryStream(buffer, (Int32)bufferLen, (Int32)bufferLen, FileAccess.Read);
// Create a byte array to hold data from unmanaged memory.
byte[] data = new byte [bufferLen];
// Read from unmanaged memory to the byte array.
readStream.Read(data , 0, bufferLen);
// Don't forget to free the block of unmanaged memory!!!
Marshal.FreeHGlobal(buffer);
再次的我还没有编译或运行代码的，但它应该让你在正确的轨道上。
Again, I have not compiled or run the code, but it should get you on the right track.
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