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实例讲解:.NET如何访问MySQL数据库

时间:2009-11-14 17:53:16  来源:互联网  作者:未知

  .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);
 
     }
}
  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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