初学SqlHelper - 实现增删改查

 //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;
           }
         }
       }

- SqlHelper

 /// <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("", "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 - ) + ") id from Contact)";
             var DataSource = SqlHelper.ExecuteDataTable(sql);
             string JsonString = string.Empty;
             JsonString = JsonConvert.SerializeObject(DataSource);
             return ReturnJson(new ResponseModel("", "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("","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 == )
             {
                 return ReturnJson(new ResponseModel("", "成功", ""));
             }
             return ReturnJson(new ResponseModel("", "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 == )
             {
                 return ReturnJson(new ResponseModel("", "成功", ""));
             }
             return ReturnJson(new ResponseModel("", "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 == )
             {
                 return ReturnJson(new ResponseModel("", "成功", ""));
             }
             return ReturnJson(new ResponseModel("", "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; }
     }