如何使用 .NET访问MySQL数据库

　.NET的数据库天然支持MSSQLServer，但是并非其他数据库不支持，而是微软基于自身利益需要，在支持、营销上推自己的数据库产品;但是作为平台战略，他并非排斥其他数据库，而是参考java体系提出了一套数据库访问规范，让各个第三方进行开发，提供特定的驱动。

　　MySQL是免费的数据库，在成本上具有无可替代的优势，但是目前来讲，并没有提供。微软把MySQL当作ODBC数据库，可以按照ODBC.Net规范进行访问，具体参考

　　http://www.microsoft.com/china/community/Columns/Luyan/6.mspx

　　而实际上，针对ODBC。Net的需要配置DSN的麻烦，而是出现了一个开源的系统MySQLDriverCS，对MySQL的开发进行了封装，实现了.net环境下对于MySQL数据库系统的访问。

　　http://sourceforge.net/projects/mysqldrivercs/

　　通过阅读源代码，我们看到MySQLDriverCS的思路是利用C函数的底层库来操纵数据库的，通常提供对MySQL数据库的访问的数据库的C DLL是名为libmySQL.dll的驱动文件，MySQLDriverCS作为一个.net库进行封装C风格的驱动。

　　具体如何进行呢?

　　打开工程后，我们看到其中有一个比较特殊的.cs文件CPrototypes.cs：

以下是引用片段：

#region LICENSE
/*
MySQLDriverCS: An C# driver for MySQL.
Copyright (c) 2002 Manuel Lucas Vi馻s Livschitz.

This file is part of MySQLDriverCS.

MySQLDriverCS is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

MySQLDriverCS is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with MySQLDriverCS; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

*/
#endregion
using System;
using System.Data;
using System.Runtime.InteropServices;
namespace MySQLDriverCS
{

//[StructLayout(LayoutKind.Sequential)]
public class MYSQL_FIELD_FACTORY
{
static string version;
public static IMYSQL_FIELD GetInstance()
{

if (version==null)
{
version = CPrototypes.GetClientInfo();
}
if (version.CompareTo("4.1.2-alpha")＞=0)
{
return new MYSQL_FIELD_VERSION_5();
}
else
return new MYSQL_FIELD_VERSION_3();
}
}
public interface IMYSQL_FIELD
{
string Name{get;}
uint Type{get;}
long Max_Length {get;}
}
///＜summary＞
/// Field descriptor
///＜/summary＞
[StructLayout(LayoutKind.Sequential)]//"3.23.32", 4.0.1-alpha
internal class MYSQL_FIELD_VERSION_3: IMYSQL_FIELD
{
///＜summary＞
/// Name of column
///＜/summary＞

public string name;
///＜summary＞
/// Table of column if column was a field
///＜/summary＞
public string table;
//public string org_table; /* Org table name if table was an alias */
//public string db; /* Database for table */
///＜summary＞
/// def
///＜/summary＞
public string def;
///＜summary＞
/// length
///＜/summary＞
public long length;
///＜summary＞
/// max_length
///＜/summary＞
public long max_length;
///＜summary＞
/// Div flags
///＜/summary＞
public uint flags;
///＜summary＞
/// Number of decimals in field
///＜/summary＞
public uint decimals;
///＜summary＞
/// Type of field. Se mysql_com.h for types
///＜/summary＞
public uint type;

///＜summary＞
/// Name
///＜/summary＞

public string Name
{
get{return name;}
}
///＜summary＞
/// Type
///＜/summary＞
public uint Type
{
get{return type;}
}
///＜summary＞
/// Max_Length
///＜/summary＞
public long Max_Length
{
get {return max_length;}
}
}

///＜summary＞
/// Field descriptor
///＜/summary＞
[StructLayout(LayoutKind.Sequential)]
internal class MYSQL_FIELD_VERSION_5: IMYSQL_FIELD
{
///＜summary＞
/// Name of column
///＜/summary＞
public string name;
///＜summary＞
/// Original column name, if an alias
///＜/summary＞
public string org_name;
///＜summary＞
/// Table of column if column was a field
///＜/summary＞
public string table;
///＜summary＞
/// Org table name if table was an alias
///＜/summary＞

public string org_table;
///＜summary＞
/// Database for table
///＜/summary＞
public string db;
///＜summary＞
/// Catalog for table
///＜/summary＞
//public string catalog;
///＜summary＞
/// def
///＜/summary＞
public string def;
///＜summary＞
/// length
///＜/summary＞
public long length;
///＜summary＞
/// max_length
///＜/summary＞
public long max_length;
///＜summary＞
/// name_length
///＜/summary＞
//public uint name_length;
///＜summary＞
/// org_name_length
///＜/summary＞
public uint org_name_length;
///＜summary＞
/// table_length
///＜/summary＞
public uint table_length;
///＜summary＞
/// org_table_length
///＜/summary＞
public uint org_table_length;
///＜summary＞
/// db_length
///＜/summary＞

public string org_table;
///＜summary＞
/// Database for table
///＜/summary＞
public string db;
///＜summary＞
/// Catalog for table
///＜/summary＞
//public string catalog;
///＜summary＞
/// def
///＜/summary＞
public string def;
///＜summary＞
/// length
///＜/summary＞
public long length;
///＜summary＞
/// max_length
///＜/summary＞
public long max_length;
///＜summary＞
/// name_length
///＜/summary＞
//public uint name_length;
///＜summary＞
/// org_name_length
///＜/summary＞
public uint org_name_length;
///＜summary＞
/// table_length
///＜/summary＞
public uint table_length;
///＜summary＞
/// org_table_length
///＜/summary＞
public uint org_table_length;
///＜summary＞
/// db_length
///＜/summary＞

//[StructLayout(LayoutKind.Explicit)]
public enum enum_field_types
{
FIELD_TYPE_DECIMAL, FIELD_TYPE_TINY,
FIELD_TYPE_SHORT, FIELD_TYPE_LONG,
FIELD_TYPE_FLOAT, FIELD_TYPE_DOUBLE,
FIELD_TYPE_NULL, FIELD_TYPE_TIMESTAMP,
FIELD_TYPE_LONGLONG,FIELD_TYPE_INT24,
FIELD_TYPE_DATE, FIELD_TYPE_TIME,
FIELD_TYPE_DATETIME, FIELD_TYPE_YEAR,
FIELD_TYPE_NEWDATE,
FIELD_TYPE_ENUM=247,
FIELD_TYPE_SET=248,
FIELD_TYPE_TINY_BLOB=249,
FIELD_TYPE_MEDIUM_BLOB=250,
FIELD_TYPE_LONG_BLOB=251,
FIELD_TYPE_BLOB=252,
FIELD_TYPE_VAR_STRING=253,
FIELD_TYPE_STRING=254,
FIELD_TYPE_GEOMETRY=255

};

///＜summary＞
/// C prototypes warpper for mysqllib.
///＜/summary＞
internal class CPrototypes
{
[ DllImport( "libmySQL.dll", EntryPoint="mysql_init" )]
unsafe public static extern void* mysql_init(void* must_be_null);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_close" )]
unsafe public static extern void mysql_close(void* handle);

// BEGIN ADDITION 2004-07-01 BY Alex Seewald
// Enables us to call mysql_option to activate compression and timeout
[ DllImport( "libmySQL.dll", EntryPoint="mysql_options" )]
unsafe public static extern void mysql_options(void* mysql, uint option, uint *value);
// END ADDITION 2004-07-01 By Alex Seewald

[ DllImport( "libmySQL.dll", EntryPoint="mysql_real_connect" )]
unsafe public static extern void* mysql_real_connect(void* mysql, string host, string user, string passwd, string db, uint port, string unix_socket, int client_flag);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_query" )]
unsafe public static extern int mysql_query(void*mysql, string query);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_store_result" )]
unsafe public static extern void *mysql_store_result(void *mysql);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_free_result" )]
unsafe public static extern void mysql_free_result(void*result);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_errno" )]
unsafe public static extern uint mysql_errno(void*mysql);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_error" )]
unsafe public static extern string mysql_error(void*mysql);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_field_count" )]
unsafe public static extern uint mysql_field_count(void*mysql);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_affected_rows" )]
unsafe public static extern ulong mysql_affected_rows(void*mysql);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_num_fields" )]
unsafe public static extern uint mysql_num_fields(void*result);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_num_rows" )]
unsafe public static extern ulong mysql_num_rows(void *result);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_fetch_field_direct" )]
unsafe public static extern IntPtr mysql_fetch_field_direct(void*result, uint fieldnr);

///＜returns＞Returns a string that represents the client library version＜/returns＞
[DllImport("libmySQL.dll",CharSet=System.Runtime.InteropServices.CharSet.Ansi,
EntryPoint="mysql_get_client_info", ExactSpelling=true)]
public static extern string GetClientInfo();

[ DllImport( "libmySQL.dll", EntryPoint="mysql_fetch_row" )]
unsafe public static extern IntPtr mysql_fetch_row(void*result);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_select_db" )]
unsafe public static extern int mysql_select_db(void*mysql,string dbname);
[ DllImport( "libmySQL.dll", EntryPoint="mysql_fetch_lengths" )]
unsafe public static extern UInt32 *mysql_fetch_lengths(void*result);

}
}


　　基本上是将C风格的基础数据结构进行.net的重新定义，然后通过InteropServices进行访问。

　　具体如何利用这个库进行操作，可以参考其中的例子。

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