封装SqlHelper类

using System.Data;
using System.Data.SqlClient;


namespace SqlHelperNameSpace
{
    class SqlHelper
    {
        private static readonly string ConStr = "Data Source=.;database=mlh;Integrated Security=True";
        public static int ExecuteNonQuery(string sql)
        {
            using (SqlConnection con = new SqlConnection(ConStr))
            {
                con.Open();
                using (SqlCommand cmd = new SqlCommand(sql, con))
                {
                    int a = -1;
                    a = cmd.ExecuteNonQuery();
                    con.Close();
                    return a;
                }
            }
        }
        public static int ExecuteScalar(string sql)
        {
            using (SqlConnection con = new SqlConnection(ConStr))
            {
                con.Open();
                using (SqlCommand cmd = new SqlCommand(sql, con))
                {

                    try
                    {
                        return (int)cmd.ExecuteScalar();
                    }
                    catch
                    {
                        throw;
                    }
                }
            }
        }
        public static SqlDataReader SqlDataReader(string sql)
        {
            SqlConnection con = new SqlConnection(ConStr);
            using (SqlCommand cmd = new SqlCommand(sql, con))
            {
                con.Open();
                try
                {
                    //关闭reader的同时把数据库连接给关掉
                    return cmd.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
                }
                catch
                {
                    throw;
                }
            }
        }
        public static DataTable SqlDataAdapter(string sql)
        {
            using (SqlConnection con = new SqlConnection(ConStr))
            {
                using (SqlCommand cmd = new SqlCommand(sql, con))
                {
                    con.Open();
                    DataSet ds = new DataSet();
                    try
                    {
                        SqlDataAdapter sda = new SqlDataAdapter(cmd);
                        sda.Fill(ds, "table");
                        DataTable dt = ds.Tables["table"];
                        con.Close();
                        return dt;
                    }
                    catch
                    {
                        con.Close();
                        throw;
                    }
                }
            }
        }

    }
}