判断数据库的数据是否存在

目的：判断类别名称是否已存在
1.在DAL层中SQLHelper写入代码：

        /// <summary>
        /// 该方法执行传入的SQL查询语句
        /// </summary>
        /// <param name="sql">ＳＱＬ查询语句</param>
        /// <returns></returns>
        public DataTable ExecuteQuery(string sql)
        {
            DataTable dt = new DataTable();
            string connStr = @"server=SIKU;database=newssystem;uid=sa;pwd=123456";
            SqlConnection conn = new SqlConnection(connStr);
            conn.Open();
            SqlCommand cmd = new SqlCommand(sql, conn);
            SqlDataReader  sdr = cmd.ExecuteReader();
            dt.Load(sdr);
            sdr.Close ();
            conn.Close();
            return dt;
        }
2。在DAL层中CategoryDAO中写入代码：
        /// <summary>
        /// 判断类别名称是否已存在
        /// </summary>
        /// <param name="caName">类别名称</param>
        /// <returns></returns>
        public bool IsExists(string caName)
        {
            bool flag = false;
            string sql = "select * from category where [name]='" + caName + "'";
            DataTable dt = new DataTable();
            SQLHelper sqlhelper = new SQLHelper();
            dt = sqlhelper.ExecuteQuery(sql);
            if (dt.Rows.Count > 0)
            {
                flag = true;
            }
            return flag;
        }
3.在Web层中Default.cs中输入：
public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //绑定GridView
        GridView1.DataSource = new CategoryDAO().SelectAll();
        GridView1.DataBind();

    }
    //Button事件
    protected void Button1_Click(object sender, EventArgs e)
    {
        string caName = TextBox1.Text;
        bool b = new CategoryDAO().IsExists(caName);
        Response.Write(b);
    }
}