DBHelper c#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;

namespace Demo
{
class DBHelper
{
private static string connectionString = "Data Source=.;Initial Catalog=AddressPhone;Integrated Security=True";
private SqlConnection connection = new SqlConnection(connectionString);
public SqlCommand cmd;

/// <summary>
/// 添加，删除更新
/// </summary>
/// <param name="sql"></param>
/// <returns></returns>
public bool ExecuteNonQuery(string sql)
{
try
{
connection.Open();
cmd = connection.CreateCommand();
cmd.CommandText = sql;
// 返回值是int类型，受影响的行数
if (cmd.ExecuteNonQuery() > 0)
{
return true;
}
else
{
return false;
}
}
catch (Exception e)
{

Console.WriteLine("异常消息" + e.Message);
return false;
}
finally
{
connection.Close();
}
}

/// <summary>
/// 查询
/// </summary>
/// <param name="sql"></param>
/// <returns></returns>
public List<List<object>> Query(string sql)
{
try
{
connection.Open();

cmd = connection.CreateCommand();
cmd.CommandText = sql;
SqlDataReader reader = cmd.ExecuteReader();
List<List<object>> list = new List<List<object>>();
List<object> ls = null;
while (reader.Read())
{
ls = new List<object>();
int count = reader.FieldCount;
for (int i = 0; i < count; i++)
{
ls.Add(reader.GetValue(i));
}
list.Add(ls);
}

reader.Close();
return list;
}
catch (Exception e)
{
Console.WriteLine("异常消息" + e);
return null;
}
finally
{
connection.Close();

}
}

/// <summary>
///  查询数量用
/// </summary>
/// <param name="sql"></param>
/// <returns></returns>
public int GetCount(string sql)
{
try
{
connection.Open();
cmd = connection.CreateCommand();
cmd.CommandText = sql;
int count = Convert.ToInt32(cmd.ExecuteScalar());

return count;
}
catch (Exception e)
{
Console.WriteLine("异常消息" + e);
return 0;
}
finally
{
connection.Close();

}
}

}
}