LINQ-to-SQL 查询不返回结果

发布于 2024-10-20 05:05:51 字数 581 浏览 4 评论 0原文

我有一个使用 LINQ-to-SQL 的查询。它查询底层数据库表 Rooms。它使用Where条件来缩小结果范围，即：

性别。
当前入住率 < 最大占用
已选中

可用标志我知道这应该返回结果，但它一直返回空集。有什么想法吗？代码如下

    Dim selectedHalls = (From sh In dbHalls.Rooms _
                         Where sh.gender = Session("gender").ToString _
                         Where sh.max_occupancy > sh.current_occupancy _
                         Where sh.is_available = 1 _
                         Select sh.building_name).Distinct()

更新：我已经验证问题出在语句 where sh.is_available = 1 上，这没有意义，因为这是一个位字段。

原文

I have a query using LINQ-to-SQL. It queries an underlying database table Rooms. It uses Where conditions to narrow down the results, namely:

Gender.
Current Occupancy < Max Occupancy
Available Flag is Checked

I know this should return results but it keeps returning an empty set. Any ideas? Code is below

    Dim selectedHalls = (From sh In dbHalls.Rooms _
                         Where sh.gender = Session("gender").ToString _
                         Where sh.max_occupancy > sh.current_occupancy _
                         Where sh.is_available = 1 _
                         Select sh.building_name).Distinct()

UPDATE: I've verified that the issue is with the statement where sh.is_available = 1, which doesn't make sense since this is a bit field.

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高跟鞋的旋律 2024-10-27 05:05:52

我认为找出问题所在的最佳方法是生成 SQL 字符串，并通过直接针对数据源执行它来测试“它应该返回结果”的假设。

为此：（

      Dim sqlQuery As String =  dbHalls.GetCommand(
                    (From sh In dbHalls.Rooms _
                     Where sh.gender = Session("gender").ToString _
                     Where sh.max_occupancy > sh.current_occupancy _
                     Where sh.is_available = 1 _
                     Select sh.building_name).Distinct()
              ).CommandText

我通常使用 C#，但我认为这就是在 VB 中声明字符串的方式，对吧？）

无论如何，这将为您提供一条 SQL 语句，该语句比我们无法查看的情况下提供的任何信息都更丰富。在您的底层数据库中。

唯一让我觉得可能有问题的是 Session("gender")。您基本上依赖于要填充的 Session 对象，区分大小写的字符串键 "gender" 的值与您的 Session 中区分大小写的字符串字段 gender 相匹配。数据库。这听起来像是相当多的假设，可能会也可能不会被测试，并且可能是收到空结果的原因。

编辑
我刚刚看到你的更新。 Linq-to-sql，将位字段解释为布尔值，而不是整数值。尝试将其更改为 where sh.is_available

I think the best way to find out what the problem is to generate the SQL string and test your assumption that "it should return results" by executing it directly against the data source.

To do this:

      Dim sqlQuery As String =  dbHalls.GetCommand(
                    (From sh In dbHalls.Rooms _
                     Where sh.gender = Session("gender").ToString _
                     Where sh.max_occupancy > sh.current_occupancy _
                     Where sh.is_available = 1 _
                     Select sh.building_name).Distinct()
              ).CommandText

(I usually use C#, but I think that's how you declare a string in VB, right?)

Anyway, this will give you an SQL statement that will be more informative than anything we can give you without being able to look at your underlying database.

The only thing that jumps out at me as being potentially problematic is the Session("gender"). You are basically relying on your Session object to be populated, have a value for the case-sensitive string key "gender" that matches the case-sensitive string field gender in your database. This sounds like quite a few assumptions, that may or may not be tested and could be the reason for receiving empty results.

EDIT
I just saw your update. Linq-to-sql, interprets a bit field as a boolean value, not an integer value. Try changing it to just where sh.is_available

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