Question

我一直按照本指南中的建议设置SignalR，以便实时向客户端推送数据库更新：

https://www.codeproject.com/Tips/1075852/ASP-NET-MVC-SignalR-SqlDependency-and-EntityFramew?fid=1899771&df=90&mpp=25&sort=Position&spc=Relaxed&prof=True&view=Normal&fr=26

在我的控制器中使用简单的Linq查询时，一切正常：

public async Task<ActionResult> Messages()
{
    var collection = db.Messages;
    ViewBag.NotifierEntity = db.GetNotifierEntity<Message>(collection).ToJson();

    return View(await collection.ToListAsync());
}

但每当我想做一些稍微复杂的事情，比如：

public async Task<ActionResult> Messages()
{
    var username = CurrentUser().UserName;
    var collection = db.Messages.Where(m => m.Recipients
        .All(u => u.UserName == username));
    ViewBag.NotifierEntity = db.GetNotifierEntity<Message>(collection).ToJson();
    return View(await collection.ToListAsync());
}

我从JavaScriptSerializer收到有关循环引用的错误。我切换到Json.Net序列化器：

public static NotifierEntity FromJson(string value)
{
    if (String.IsNullOrEmpty(value))
        throw new ArgumentNullException("NotifierEntity Value can not be null.");

    //return new JavaScriptSerializer().Deserialize<NotifierEntity>(value);
    return JsonConvert.DeserializeObject<NotifierEntity>(value, new JsonSerializerSettings { 
        NullValueHandling = NullValueHandling.Ignore
    });
}

但是现在我在访问该页面时收到以下异常：

[Newtonsoft.Json.JsonSerializationException] {"Error converting value \"p__linq__0\" to type 'System.Data.SqlClient.SqlParameter'. Path 'SqlParameters[0]', line 1, position 1010."}

[InnerException] {"Could not cast or convert from System.String to System.Data.SqlClient.SqlParameter."}

但View本身似乎正确呈现。有人可以帮忙吗？

编辑：值包含以下内容：

"{\"SqlQuery\":\"SELECT \\r\\n    1 AS [C1], \\r\\n    [Extent1].[ID] AS [ID], \\r\\n    [Extent1].[Date] AS [Date], \\r\\n    [Extent1].[Title] AS [Title], \\r\\n    [Extent1].[Content] AS [Content], \\r\\n    [Extent1].[Read] AS [Read], \\r\\n    [Extent1].[Sender_Id] AS [Sender_Id]\\r\\n    FROM [dbo].[Messages] AS [Extent1]\\r\\n    WHERE  NOT EXISTS (SELECT \\r\\n        1 AS [C1]\\r\\n        FROM [dbo].[AspNetUsers] AS [Extent2]\\r\\n        WHERE ([Extent1].[ID] = [Extent2].[Message_ID]) AND (( NOT (([Extent2].[UserName] = @p__linq__0) AND (0 = (CASE WHEN (@p__linq__0 IS NULL) THEN cast(1 as bit) ELSE cast(0 as bit) END)))) OR (CASE WHEN ([Extent2].[UserName] = @p__linq__0) THEN cast(1 as bit) WHEN ( NOT (([Extent2].[UserName] = @p__linq__0) AND (0 = (CASE WHEN (@p__linq__0 IS NULL) THEN cast(1 as bit) ELSE cast(0 as bit) END)))) THEN cast(0 as bit) END IS NULL))\\r\\n    )\",\"SqlConnectionString\":\"Data Source=(LocalDb)\\\\MSSQLLocalDB;Initial Catalog=PrismContext;Integrated Security=SSPI;\",\"SqlPa
rameters\":[\"p__linq__0\"]}"

编辑2：GetNotifierEntity定义为：

public static NotifierEntity GetNotifierEntity<TEntity>(this DbContext dbContext, IQueryable iQueryable) where TEntity : EntityBase
{
    var objectQuery = dbContext.GetObjectQuery<TEntity>(iQueryable);
    return new NotifierEntity()
    {
        SqlQuery = objectQuery.ToTraceString(),
        SqlConnectionString = objectQuery.SqlConnectionString(),
        SqlParameters = objectQuery.SqlParameters()
    };
}

Json.Net反序列化转换值p_linq_0的错误

0 个答案: