/// <summary>
  /// 数据库访问通用类
  /// </summary>
  public class SqlHelper
  {
  private string connectionString;
  /// <summary>
  /// 设定数据库访问字符串
  /// </summary>
  public string ConnectionString
  {
  set { connectionString = value; }
  }
  /// <summary>
  /// 构造函数
  /// </summary>
  /// <param name="connectionString">数据库访问字符串</param>
  public SqlHelper(string connectionString)
  {
  this.connectionString = connectionString;
  }
  /// <summary>
  /// 执行一个查询，并返回查询结果
  /// </summary>
  /// <param name="sql">要执行的sql语句</param>
  /// <param name="commandType">要执行的查询语句的类型，如存储过程或者sql文本命令</param>
  /// <returns>返回查询结果集</returns>
  public DataTable ExecuteDataTable(string sql,CommandType commandType)
  {
  return ExecuteDataTable(sql, commandType, null);
  }
  /// <summary>
  /// 执行一个查询，并返回结果集
  /// </summary>
  /// <param name="sql">要执行的sql文本命令</param>
  /// <returns>返回查询的结果集</returns>
  public DataTable ExecuteDataTable(string sql)
  {
  return ExecuteDataTable(sql, CommandType.Text, null);
  }
  /// <summary>
  /// 执行一个查询，并返回查询结果
  /// </summary>
  /// <param name="sql">要执行的sql语句</param>
  /// <param name="commandtype">要执行查询语句的类型，如存储过程或者sql文本命令</param>
  /// <param name="parameters">Transact-SQL语句或者存储过程参数数组</param>
  /// <returns></returns>
  public DataTable ExecuteDataTable(string sql, CommandType commandtype, SqlParameter[] parameters)
  {
  DataTable data = new DataTable(); //实例化datatable，用于装载查询结果集
  using (SqlConnection con = new SqlConnection(connectionString))
  {
  using (SqlCommand cmd = new SqlCommand(sql, con))
  {
  cmd.CommandType = commandtype;//设置command的commandType为指定的Commandtype
  //如果同时传入了参数，则添加这些参数
  if (parameters != null)
  {
  foreach (SqlParameter parameter in parameters)
  {
  cmd.Parameters.Add(parameter);
  }
  }
  //通过包含查询sql的sqlcommand实例来实例化sqldataadapter
  SqlDataAdapter adapter = new SqlDataAdapter(cmd);
  adapter.Fill(data);//填充datatable
  }
  }
  return data;
  }
  /// <summary>
  /// 返回一个SqlDataReader对象的实例
  /// </summary>
  /// <param name="sql">要执行的SQl查询命令</param>
  /// <returns></returns>
  public SqlDataReader ExecuteReader(string sql)
  {
  return ExecuteReader(sql, CommandType.Text, null);
  }
  /// <summary>
  ///
  /// </summary>
  /// <param name="sql">要执行的sql语句</param>
  /// <param name="commandType">要执行查询语句的类型，如存储过程或者SQl文本命令</param>
  /// <returns></returns>
  public SqlDataReader ExecuteReader(string sql,CommandType commandType)
  {
  return ExecuteReader(sql, commandType, null);
  }
  /// <summary>
  /// 返回一个sqldatareader对象的实例
  /// </summary>
  /// <param name="sql"></param>
  /// <param name="commandType"></param>
  /// <param name="parameters"></param>
  /// <returns></returns>
  public SqlDataReader ExecuteReader(string sql, CommandType commandType, SqlParameter[] parameters)
  {
  SqlConnection con = new SqlConnection(connectionString);
  SqlCommand cmd = new SqlCommand(sql, con);
  if (parameters != null)
  {
  foreach (SqlParameter parameter in parameters)
  {
  cmd.Parameters.Add(parameters);
  }
  }
  con.Open();
  //CommandBehavior.CloseConnection参数指示关闭reader对象时关闭与其关联的Connection对象
  return cmd.ExecuteReader(CommandBehavior.CloseConnection);
  }
  /// <summary>
  /// 执行一个查询，返回结果集的首行首列。忽略其他行，其他列
  /// </summary>
  /// <param name="sql">要执行的SQl命令</param>
  /// <returns></returns>
  public Object ExecuteScalar(string sql)
  {
  return ExecuteScalar(sql, CommandType.Text, null);
  }
  /// <summary>
  ///
  /// </summary>
  /// <param name="sql"></param>
  /// <param name="commandType"></param>
  /// <returns></returns>
  public Object ExecuteScalar(string sql, CommandType commandType)
  {
  return ExecuteScalar(sql, commandType, null);
  }
  /// <summary>
  ///
  /// </summary>
  /// <param name="sql"></param>
  /// <param name="commandType">参数类型</param>
  /// <param name="parameters"></param>
  /// <returns></returns>
  public Object ExecuteScalar(string sql,CommandType commandType, SqlParameter[] parameters)
  {
  Object result=null;
  SqlConnection con=new SqlConnection(connectionString);
  SqlCommand cmd=new SqlCommand(sql,con);
  cmd.CommandType= commandType;
  if(parameters!=null)
  {
  foreach (SqlParameter parapmeter in parameters)
  {
  cmd.Parameters.Add(parapmeter);
  }
  }
  con.Open();
  result=cmd.ExecuteScalar();
  con.Close();
  return result;
  }
  /// <summary>
  /// 对数据库进行增删改的操作
  /// </summary>
  /// <param name="sql">要执行的sql命令</param>
  /// <returns></returns>
  public int ExecuteNonQuery(string sql)
  {
  return ExecuteNonQuery(sql, CommandType.Text, null);
  }
  /// <summary>
  /// 数据库进行增删改的操作
  /// </summary>
  /// <param name="sql">对数据库进行操作的sql命令</param>
  /// <param name="commandType">要执行查询语句的类型，如存储过程或者sql文本命令</param>
  /// <returns></returns>
  public int ExecuteNonQuery(string sql, CommandType commandType)
  {
  return ExecuteNonQuery(sql, commandType, null);
  }
  /// <summary>
  /// 对数据库进行增删改的操作
  /// </summary>
  /// <param name="sql">要执行的sql语句</param>
  /// <param name="commandType">要执行的查询语句类型，如存储过程或者sql文本命令</param>
  /// <param name="parameters">Transact-SQL语句或者存储过程的参数数组</param>
  /// <returns></returns>
  public int ExecuteNonQuery(string sql, CommandType commandType, SqlParameter[] parameters)
  {
  int count = 0;
  SqlConnection con = new SqlConnection(connectionString);
  SqlCommand cmd = new SqlCommand(sql, con);
  cmd.CommandType = commandType;
  if (parameters != null)
  {
  foreach(SqlParameter parameter in parameters)
  {
  cmd.Parameters.Add(parameter);
  }
  }
  con.Open();
  count = cmd.ExecuteNonQuery();
  con.Close();
  return count;
  }
  /// <summary>
  /// 返回当前连接的数据库中所有用户创建的数据库
  /// </summary>
  /// <returns></returns>
  public DataTable GetTables()
  {
  DataTable table = null;
  using (SqlConnection con = new SqlConnection(connectionString))
  {
  con.Open();
  table = con.GetSchema("Tables");
  }
  return table;
  }
  }