让我们实例讲解一下.NET如何访问MySQL数据库
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.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?
编程语言（programming language），是用来定义计算机程序的形式语言。它是一种被标准化的交流技巧，用来向计算机发出指令。一种计算机语言让程序员能够准确地定义计算机所需要使用的数据，并精确地定义在不同情况下所应当采取的行动。[1]
最早的编程语言是在电脑发明之后产生的，当时是用来控制提花织布机及自动演奏钢琴的动作。在电脑领域已发明了上千不同的编程语言，而且每年仍有新的编程语言诞生。很多编程语言需要用指令方式说明计算的程序，而有些编程语言则属于声明式编程，说明需要的结果，而不说明如何计算。编辑语言排行榜
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
*/c语言编程入门
#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;}
}
///
/// Field descriptor
///
[StructLayout(LayoutKind.Sequential)]//”3.23.32″, 4.0.1-alpha
internal class MYSQL_FIELD_VERSION_3: IMYSQL_FIELD
{
///
/// Name of column
///
public string name;
///
/// Table of column if column was a field
///
public string table;
//public string org_table; /* Org table name if table was an alias */
//public string db; /* Database for table */
///
/// def
///
public string def;
///
/// length
///
public long length;
///
/// max_length
///
public long max_length;
///
/// Div flags
///
public uint flags;
///
/// Number of decimals in field
///
public uint decimals;
///
/// Type of field. Se mysql_com.h for types
///
public uint type;
///
/// Name
///
public string Name
{
get{return name;}
}
///
/// Type
///
public uint Type
{
get{return type;}
}
///
/// Max_Length
///
public long Max_Length
{
get {return max_length;}
}
}
///
/// Field descriptor
///
[StructLayout(LayoutKind.Sequential)]
internal class MYSQL_FIELD_VERSION_5: IMYSQL_FIELD
{
///
/// Name of column
///
public string name;
///
/// Original column name, if an alias
///
public string org_name;
///
/// Table of column if column was a field
///
public string table;
///
/// Org table name if table was an alias
///
public string org_table;
///
/// Database for table
///
public string db;
///
/// Catalog for table
///
//public string catalog;
///
/// def
///
public string def;
///
/// length
///
public long length;
///
/// max_length
///
public long max_length;
///
/// name_length
///
//public uint name_length;
///
/// org_name_length
///
public uint org_name_length;
///
/// table_length
///
public uint table_length;
///
/// org_table_length
///
public uint org_table_length;
///
/// db_length
///
public uint db_length;
///
/// catalog_length
///
public uint catalog_length;
///
/// def_length
///
public uint def_length;
///
/// Div flags
///
public uint flags;
///
/// Number of decimals in field
///
public uint decimals;
///
/// Character set
///
public uint charsetnr;
///
/// Type of field. Se mysql_com.h for types
///
public uint type;
///
/// Name
///
public string Name
{
get {return name;}
}
///
/// Type
///
public uint Type
{
get {return type;}
}
///
/// Max_Length
///
public long Max_Length
{
get {return max_length;}
}
}
//[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
};
///
/// C prototypes warpper for mysqllib.
///
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 a string that represents the client library version
[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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