ADO.NET无连接模式的详细介绍

无连接模式：可以在没有打开连接时在内存中操作数据，dataadapter通过管理连接为无连接模式提供服务，当要从数据库中查询数据时，dataadapter打开一个连接，填充指定的dataset,等数据读取完马上自动关闭连接，然后可以对数据做修改，再次使用dataadapter打开连接，持久化修改(无论是更新，删除或是更新)，最后自动关闭连接，使用无连接模式的情况是有一些独立数据，它们不会发生改变或者很少改变，因为在将填充dataset和更新数据这段时间内数据库中的实际数据也许会发生改变，如果需要将数据立即持久化到数据库请使用连接模式

读取数据到dataset:无连接意味着一个连接建立了一个与数据库的会话，请求的数据读入到dataset中，然后通过断开数据库的连接关闭会话，这时会话因为与数据库的断开而关闭，dataset成为一个无连接的数据库

/// <summary>
      /// 查询学生信息
      /// </summary>
      /// <returns>返回填充了学生表的dataset</returns>
      public dataset getuserinfor()
      {
          string str = "data source=.;initial catalog=student;integrated security=true";
          var conn = new sqlconnection(str);
          dataset ds = new dataset();
          var sda = new sqldataadapter("select * from student",conn);
          sda.fill(ds, "student");//调用fill方法时，sqldataadapter会自动打开连接，读取数据然后关闭连接
          foreach (datarow dr in ds.tables["student"].rows)
          {
              console.writeline(dr["name"]);
          }
          return ds;
      }

将dataset的修改保存到数据库
插入数据

/// <summary>
      /// 插入学生信息，并返回插入后的dataset
      /// </summary>
      /// <param name="stu">学生实体类</param>
      public dataset insertstudnt(student stu)
      {
          dataset ds = getuserinfor();
          string str = "data source=.;initial catalog=student;integrated security=true";
          string sql = "insert into student values (@name,@age)";
          var conn = new sqlconnection(str);
          var cmd = new sqlcommand(sql,conn);
          var sda = new sqldataadapter();
          sqlparameter sqlparam1 = new sqlparameter()
          {
              parametername = "@name",
              sourcecolumn = "name"
          };
          sqlparameter sqlparam2 = new sqlparameter()
          {
              parametername = "@age",
              sourcecolumn = "age"
          };
          sqlparameter[] sqlparamarray = new sqlparameter[] {sqlparam1,sqlparam2 };
          cmd.parameters.addrange(sqlparamarray);
          sda.insertcommand = cmd;
          datarow dr = ds.tables["student"].newrow();
          dr["name"] = stu.name;
          dr["age"] = stu.age;
          ds.tables["student"].rows.add(dr);
          sda.update(ds,"student");
          return ds;

      }

更新数据

/// <summary>
      /// 根据id更新姓名和年龄
      /// </summary>
      /// <param name="name">姓名</param>
      /// <param name="age">年龄</param>
      /// <param name="id">学生id</param>
      /// <returns>返回更新后的dataset</returns>
      public dataset updatestudent(student stu,int id)
      {
          dataset ds = getuserinfor();
          string str = "data source=.;initial catalog=student;integrated security=true";
          string sql = "update student set name=@name,age=@age where id=@id";
          var conn = new sqlconnection(str);
          var cmd = new sqlcommand(sql, conn);
          var sda = new sqldataadapter();
          sqlparameter param1 = new sqlparameter()
          {
              parametername="@name",sourcecolumn="name"
          };
          sqlparameter param2 = new sqlparameter()
          {
              parametername = "@age",
              sourcecolumn = "age",
              sqldbtype=sqldbtype.int
          };
          sqlparameter param3 = new sqlparameter()
          {
              parametername = "@id",
              sourcecolumn = "id"
          };
          sqlparameter[] param = new sqlparameter[] {param1,param2,param3 };
          cmd.parameters.addrange(param);
          sda.updatecommand = cmd;
          datatable dt = ds.tables["student"];
          foreach (datarow dr in dt.rows)
          {
              int oldid=convert.toint32(dr["id"]);
              if (oldid == id)
              {
                  dr["name"] = stu.name;
                  dr["age"] = stu.age;
              }
          }
          sda.update(ds,"student");
          return ds;
      }

删除数据

/// <summary>
      /// 根据id删除一个学生
      /// </summary>
      /// <param name="id">返回更新后的dataset</param>
      public dataset deletestudent(int id)
      {
          dataset ds = getuserinfor();
          string str = "data source=.;initial catalog=student;integrated security=true";
          string sql = "delete from student where id=@id";
          var conn = new sqlconnection(str);
          var cmd = new sqlcommand(sql, conn);
          var sda = new sqldataadapter();
          sqlparameter param = new sqlparameter()
          {
              parametername="@id",sourcecolumn="id",sqldbtype=sqldbtype.int
          };
          cmd.parameters.add(param);
          sda.deletecommand = cmd;
          datatable dt=ds.tables["student"];
          foreach (datarow dr in dt.rows)
          {
              int oldid = convert.toint32(dr["id"]);
              if (oldid == id)
                  dr.delete();
          }
          sda.update(ds,"student");
          return ds;
      }