初学SqlHelper

//数据库连接字符串
      public static readonly string constr = ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;

      //打开数据库
      public static SqlConnection OpenConnection()
      {
        SqlConnection conn = new SqlConnection(constr);
        conn.Open();
        return conn;
      }

      //执行不返回结果的sql，用于插入和更新，删除
      public static int ExecuteNonQuery(string cmdText, params SqlParameter[] parameters)
      {
        using (SqlConnection conn = new SqlConnection(constr))
        {
          conn.Open();
          return ExecuteNonQuery(conn, cmdText, parameters);
        }
      }

      //上面方法的重载方法
      public static int ExecuteNonQuery(SqlConnection conn, string cmdText, params SqlParameter[] parameters)
      {
        using (SqlCommand cmd = conn.CreateCommand())
        {
          cmd.CommandText = cmdText;
          cmd.Parameters.AddRange(parameters);
          return cmd.ExecuteNonQuery();
        }
      }

      //返回对象类型的sql查询，对象单个数据记录的中的某个值，或者count(*)计算的结果，在分页中会经常用到。
      public static object ExecuteScalar(string cmdText, params SqlParameter[] parameters)
      {
        using (SqlConnection conn = new SqlConnection(constr))
        {
          conn.Open();
          return ExecuteScalar(conn, cmdText, parameters);
        }
      }

      //以上方法的重载方法
      public static object ExecuteScalar(SqlConnection conn, string cmdText, params SqlParameter[] parameters)
      {
        using (SqlCommand cmd = conn.CreateCommand())
        {
          cmd.CommandText = cmdText;
          cmd.Parameters.AddRange(parameters);
          return cmd.ExecuteScalar();
        }
      }

      //获得数据表格的查询
      public static DataTable ExecuteDataTable(string cmdText, params SqlParameter[] parameters)
      {
        using (SqlConnection conn = new SqlConnection(constr))
        {
          conn.Open();
          return ExecuteDataTable(conn, cmdText, parameters);
        }
      }

      //以上方法的重载
      public static DataTable ExecuteDataTable(SqlConnection conn, string cmdText, params SqlParameter[] parameters)
      {
        using (SqlCommand cmd = conn.CreateCommand())
        {
          cmd.CommandText = cmdText;
          cmd.Parameters.AddRange(parameters);
          using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))
          {
            DataTable dt = new DataTable();
            adapter.Fill(dt);
            return dt;
          }
        }
      }

/// <summary>
        /// 查询表中总记录
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public async Task<ActionResult> ScalarData(ContactModel data)
        {
            string sql = "select count(*) from Contact";
            var DataSource = SqlHelper.ExecuteScalar(sql);
            return ReturnJson(new ResponseModel("0000", "成功", "共有记录"+DataSource.ToString()+"条"));
        }
        /// <summary>
        /// 分页查询表中数据
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public async Task<ActionResult> SelectPageData(ContactModel data)
        {
            int pageindex = data.pageindex;
            int pagesize = data.pagesize;
            string sql = "select top " + pagesize + " * from Contact where id not in (select top (" + pagesize * (pageindex - 1) + ") id from Contact)";
            var DataSource = SqlHelper.ExecuteDataTable(sql);
            string JsonString = string.Empty;
            JsonString = JsonConvert.SerializeObject(DataSource);
            return ReturnJson(new ResponseModel("0000", "成功", JsonString));
        }
        /// <summary>
        /// 查询表中所有数据
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public async Task<ActionResult> SelectData(ContactModel data)
        {
            string sql = "select * from Contact";
            //string sql = "select * from Contact where Name=ISNULL('" + data.name + "',Name)";
            var DataSource = SqlHelper.ExecuteDataTable(sql);

            //string sql = "select * from Contact where Name=ISNULL(@Name,Name)";
            //var DataSource = SqlHelper.ExecuteDataTable(sql, new SqlParameter("@Name", data.name));
            string JsonString = string.Empty;
            JsonString = JsonConvert.SerializeObject(DataSource);
            return ReturnJson(new ResponseModel("0000","成功", JsonString));
        }
        /// <summary>
        /// 在表中插入一条新的数据
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public async Task<ActionResult> InsertData(ContactModel data)
        {
            //string sql = "INSERT INTO Contact VALUES ('"+ data.name+"','"+data.enrollmentDate+"')";
            string sql = "INSERT INTO Contact VALUES (@name, @enrollmentDate)";
            SqlParameter[] param = new SqlParameter[] {
                new SqlParameter("@name",data.name),
                new SqlParameter("@enrollmentDate",data.enrollmentDate),
            };
            var DataSource = SqlHelper.ExecuteNonQuery(sql, param);
            if (DataSource == 1)
            {
                return ReturnJson(new ResponseModel("0000", "成功", ""));
            }
            return ReturnJson(new ResponseModel("9999", "处理失败", ""));
        }
        /// <summary>
        /// 根据id修改表中的数据
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public async Task<ActionResult> UpdateData(ContactModel data)
        {
            if (data.id == null)
            {
                return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
            }
            //string sql = "UPDATE Contact SET Name = '"+ data.name + "',EnrollmentDate = '" + data.enrollmentDate + "' WHERE ID = " + data.id;
            string sql = "UPDATE Contact SET Name = @name , EnrollmentDate = @enrollmentDate  WHERE ID = @id";
            SqlParameter[] param = new SqlParameter[] {
                new SqlParameter("@id",data.id),
                new SqlParameter("@name",data.name),
                new SqlParameter("@enrollmentDate",data.enrollmentDate),
            };
            var DataSource = SqlHelper.ExecuteNonQuery(sql, param);
            if (DataSource == 1)
            {
                return ReturnJson(new ResponseModel("0000", "成功", ""));
            }
            return ReturnJson(new ResponseModel("9999", "处理失败", ""));
        }
        /// <summary>
        /// 根据id删除表中的数据
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public async Task<ActionResult> DeleteData(ContactModel data)
        {
            string sql = "DELETE FROM Contact WHERE ID = @id";
            SqlParameter[] param = new SqlParameter[] {
                new SqlParameter("@id",data.id)
            };
            var DataSource = SqlHelper.ExecuteNonQuery(sql, param);
            if (DataSource == 1)
            {
                return ReturnJson(new ResponseModel("0000", "成功", ""));
            }
            return ReturnJson(new ResponseModel("9999", "处理失败", ""));
        }

        public JsonResult ReturnJson(ResponseModel response)
        {
            return this.Json(response, JsonRequestBehavior.AllowGet);
        }

 public class ContactModel
    {
        public int id { get; set; }
        public string name { get; set; }
        public string enrollmentDate { get; set; }
        public int pageindex { get; set; }
        public int pagesize { get; set; }
    }