实例讲解：.NET如何访问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 uint db_length;          ///<summary>          /// catalog_length          ///</summary>          public uint catalog_length;          ///<summary>          /// def_length          ///</summary>          public uint def_length;          ///<summary>          /// Div flags          ///</summary>          public uint flags;                  ///<summary>          /// Number of decimals in field          ///</summary>          public uint decimals;               ///<summary>          /// Character set          ///</summary>          public uint charsetnr;              ///<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;}          }      }         //[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);        } }

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