[英]SqlDependency.OnChange firing but SqlDataReader is not returning with data
当我使用datetime列过滤器执行查询时
WHERE [Order].CreatedOn >= @CreatedOn
使用SqlDependency
,对数据源的更改将触发SqlDependency.OnChange
事件,但与SqlCommand
关联的SqlDataReader
不会返回数据( reader.HasRows
始终返回false
)。
当我只是将我的SQL语句中的过滤条件更改为
WHERE [Order].StatusId = 1"
它只是工作正常, SqlDataReader
返回数据( reader.HasRows
返回true
)
码:
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace SignalRServer
{
public partial class DepartmentScreen : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
var u = System.Security.Principal.WindowsIdentity.GetCurrent().User;
var UserName = u.Translate(Type.GetType("System.Security.Principal.NTAccount")).Value;
CheckForNewOrders(DateTime.Now);
}
private void CheckForNewOrders(DateTime dt)
{
string json = null;
string conStr = ConfigurationManager.ConnectionStrings["connString"].ConnectionString;
using (SqlConnection connection = new SqlConnection(conStr))
{
string query = string.Format(@"
SELECT [Order].OrderId
FROM [dbo].[Order]
WHERE [Order].CreatedOn >= @CreatedOn");
// query = string.Format(@"
// SELECT [Order].OrderId
// FROM [dbo].[Order]
// WHERE [Order].StatusId = 1");
using (SqlCommand command = new SqlCommand(query, connection))
{
command.Parameters.Add("@CreatedOn", SqlDbType.DateTime);
command.Parameters["@CreatedOn"].Value = DateTime.Now;
command.Notification = null;
SqlDependency dependency = new SqlDependency(command);
dependency.OnChange += new OnChangeEventHandler(dependency_OnChange);
connection.Open();
SqlDataReader reader = command.ExecuteReader();
if (reader.HasRows)
{
reader.Read();
json = reader[0].ToString();
}
}
}
SignalRHub hub = new SignalRHub();
hub.OrderReceived(json, null);
}
private void dependency_OnChange(object sender, SqlNotificationEventArgs e)
{
if (e.Type == SqlNotificationType.Change)
{
CheckForNewOrders(DateTime.Now);
}
else
{
//Do somthing here
//Console.WriteLine(e.Type);
}
}
}
}
图片:
从onchange
事件调用方法CheckForNewOrders
command.Parameters.Add("@CreatedOn", SqlDbType.DateTime);
command.Parameters["@CreatedOn"].Value = DateTime.Now;
对于参数@CreatedOn
您传递DateTime.Now
(不是其更改的时间)。 在数据库中不会有任何满足条件的数据。
将DateTime.Now作为引用日期传递时,您不太可能检索在某个时间点创建的记录(除非将来创建记录,因此您的服务器时间或列名称有问题) “createdOn”非常具有误导性。
要根据某个更新日期获取最新记录,您需要执行以下操作:
_refDate
,初始化为您选择的值,在我的情况下为DateTime.MinValue以获取第一次调用中的所有记录,然后仅以递增方式获取它们,也可以采取DateTime.Now在一个时刻开始) dependency_OnChange
事件被触发时,您需要使用_refDate
的最后一个值触发查询,以便获取尚未检索到的所有内容 _refDate
的值,依此类推。 没有测试,但这应该工作(照顾_refDate全局可访问)
public partial class DepartmentScreen : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
var u = System.Security.Principal.WindowsIdentity.GetCurrent().User;
var UserName = u.Translate(Type.GetType("System.Security.Principal.NTAccount")).Value;
CheckForNewOrders(_refDate);
}
private DateTime _refDate = DateTime.MinValue;
private void CheckForNewOrders(DateTime dt)
{
string json = null;
string conStr = ConfigurationManager.ConnectionStrings["connString"].ConnectionString;
using (SqlConnection connection = new SqlConnection(conStr))
{
string query = string.Format(@"
SELECT [Order].OrderId, [Order].CreatedOn
FROM [dbo].[Order]
WHERE [Order].CreatedOn >= @CreatedOn");
// query = string.Format(@"
// SELECT [Order].OrderId
// FROM [dbo].[Order]
// WHERE [Order].StatusId = 1");
using (SqlCommand command = new SqlCommand(query, connection))
{
command.Parameters.Add("@CreatedOn", SqlDbType.DateTime);
command.Parameters["@CreatedOn"].Value = dt;
command.Notification = null;
SqlDependency dependency = new SqlDependency(command);
dependency.OnChange += new OnChangeEventHandler(dependency_OnChange);
connection.Open();
SqlDataReader reader = command.ExecuteReader();
if (reader.HasRows)
{
while (reader.Read())
{
//json = reader[0].ToString();
var date = Convert.ToDateTime(reader["CreatedOn"]);
if (date > _refDate)
{
_refDate = date;
}
}
}
}
}
//SignalRHub hub = new SignalRHub();
//hub.OrderReceived(json, null);
}
private void dependency_OnChange(object sender, SqlNotificationEventArgs e)
{
if (e.Type == SqlNotificationType.Change)
{
CheckForNewOrders(_refDate);
}
else
{
//Do somthing here
//Console.WriteLine(e.Type);
}
}
}
}
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