asp.net 常用数据库操作

    public SqlConnection conn = new SqlConnection(ConfigurationSettings.AppSettings["ConnStr"]);
    public SqlCommand cmd = new SqlCommand(); 
    public SqlDataAdapter objadpt = new SqlDataAdapter();
    public String sqlStr;
    DataTable dt = new DataTable();   

    public basedata()
    {
        //
        // TODO: 在此处添加构造函数逻辑
        //
    }
    /// <summary>
    /// 根据sql语句返回查询结果
    /// </summary>
    /// <param name="sqlStr"></param>
    /// <returns></returns>
    public DataTable gettable(string sqlStr)
    {     
        if(conn .State== ConnectionState.Closed)
            conn.Open();
        cmd.Connection = conn;
        cmd.CommandText = sqlStr;
        objadpt.SelectCommand = cmd;
    dt.Clear();
        objadpt.Fill(dt);
        if (conn.State == ConnectionState.Open)
           conn.Close();
        return dt;
    }

    /// <summary>
    /// 执行查询语句，返回SqlDataReader
    /// </summary>
    /// <param name="strSQL">查询语句</param>
    /// <returns>SqlDataReader</returns>
    public SqlDataReader GetReader(string sqlStr)
    {
        if (conn.State == ConnectionState.Closed)
            conn.Open();
        cmd.Connection = conn;
        cmd.CommandText = sqlStr;
        SqlDataReader myReader = cmd.ExecuteReader();
        return myReader;
        if (conn.State == ConnectionState.Open)
            conn.Close();
    }

    /// <summary>
    /// 执行sql语句，如delete或update
    /// </summary>
    /// <param name="sqlStr"></param>
    public void executecmd(string sqlStr)
        {
        if (conn.State == ConnectionState.Closed)
            conn.Open();
        cmd.Connection = conn;
        cmd.CommandText = sqlStr;
         cmd.ExecuteNonQuery();
         if (conn.State == ConnectionState.Open)
               conn.Close();
        }

    public string executecmdandback(string sqlStr)
    {
        string id;
        if (conn.State == ConnectionState.Closed)
            conn.Open();
        cmd.Connection = conn;
        cmd.CommandText = sqlStr + ";SELECT SCOPE_IDENTITY()";
        id = cmd.ExecuteScalar().ToString();//添加配偶并返回刚添加的ID
        if (conn.State == ConnectionState.Open)
            conn.Close();
        return id;
    }
    /// <summary>
    /// 按条件返回查询结果
    /// </summary>
    /// <param name="sqlStr"></param>
    /// <returns></returns>
    public string getresult(string sqlStr)
        {
            string id;
        if (conn.State == ConnectionState.Closed)
            conn.Open();
        cmd.Connection = conn;
        cmd.CommandText = sqlStr;
        id = Convert.ToString(cmd.ExecuteScalar());
        if (conn.State == ConnectionState.Open)
            conn.Close();
        return id;
}