C# 奇怪的 lambda 行为
有人可以指出为什么会发生这种情况：
我正在使用 NHibernate 和 Linq 提供程序。
失败的代码列于此处：
var sequence = session.Query<T>();
var wtfSequence = sequence.Where(x => true);
var okaySequence = sequence.Where(x => x.Id > 0);
调试显示此后的 sequence （这是一个 IQueryable）包含 2 个元素，分别是添加到数据库中。
我希望第一个 Where 语句生成该序列中的所有元素，但不幸的是它留下了 0 个元素。
（为什么？？？ )
相反，第二个 Where 语句实际上会产生 2 个元素，因为它应该起作用。
这里是NHibernate -> Sqlite 查询第一个和第二个 Where 语句。
NHibernate: select cast(count(*) as INTEGER) as col_0_0_ from "BinaryUnitProxy_IndicatorUnitDescriptor" binaryunit0_ where @p0='true';@p0 = 'True' [Type: String (0)]
NHibernate: select cast(count(*) as INTEGER) as col_0_0_ from "BinaryUnitProxy_IndicatorUnitDescriptor" binaryunit0_ where binaryunit0_.Id>@p0;@p0 = 0 [Type: Int32 (0)]
现在，如果我使用我的 InMemoryRepository 测试相同的代码，它将每个实体存储在简单的列表，(x => true) 工作得很好。
那么 - 为什么在使用 NHibernate 时会发生这种情况？这是一个错误还是我做错了什么？
谢谢。
Could someone point out why this could be happening:
I am using NHibernate and the Linq provider for it.
The code that fails is listed here:
var sequence = session.Query<T>();
var wtfSequence = sequence.Where(x => true);
var okaySequence = sequence.Where(x => x.Id > 0);
Debugging shows that sequence (which is an IQueryable<T>) after this contains 2 elements, which were added to the database.
I expect the first Where statement to yield all elements from that sequence, but unfortunately it leaves 0 elements.
(WHY???)
The second Where statement, on the contrary, actually yields 2 elements as it should work.
Here are the NHibernate -> Sqlite queries for the first and second Where statements.
NHibernate: select cast(count(*) as INTEGER) as col_0_0_ from "BinaryUnitProxy_IndicatorUnitDescriptor" binaryunit0_ where @p0='true';@p0 = 'True' [Type: String (0)]
NHibernate: select cast(count(*) as INTEGER) as col_0_0_ from "BinaryUnitProxy_IndicatorUnitDescriptor" binaryunit0_ where binaryunit0_.Id>@p0;@p0 = 0 [Type: Int32 (0)]
Now, if I test the same code with my InMemoryRepository, which stores every entity in a simple list, the (x => true) works absolutelty fine.
So - why does this happen when using NHibernate? Is this a bug or I am doing something wrong?
Thank you.
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评论（3）
我不了解 NHibernate，但从生成的 SQL 中问题很明显：您的数据库不认为 true（小写 t）等于 True（大写 T）。在 SQL Server 中，您可以通过修改数据库排序规则来更改此设置（这是一个非常糟糕的主意，除非您出于其他原因希望不区分大小写）。
我的猜测是这是 NHibernate 中的一个错误，您需要解决它。测试
t => 1 == 1而不是t => true，这可能会起作用，具体取决于 NHibernate 代码的编写方式。I don't know NHibernate, but the problem is obvious from the generated SQL: Your database does not consider true (lowercase t) equal to True (uppercase T). In SQL server you can change this by modifying the database collation (which is a really bad idea unless you want case insensitivity for other reasons).
My guess is this is a bug in NHibernate that you need to work around. Test
t => 1 == 1instead oft => true, which might work depending on how the NHibernate code is written.我的猜测是，根据您显示的 SqLite 输出，这是 NHibernate 中的一个错误。您可以尝试
X => X.Id == X.Id而不是X => true并看看是否有效。My guess is that this is a bug in NHibernate based on the SqLite output that you show. You could try
X => X.Id == X.Idrather thanX => trueand see if that works.对我来说看起来像一个错误。它将布尔运算转换为字符串计算，甚至搞砸了，因为它使用
true设置查询并使用True进行计算，因此区分大小写的测试将失败。Looks like a bug to me. Its converting a boolean operation to a string evaluation, and even that's screwed up, as it sets up the query with
trueand evaluates usingTrue, so a case-sensitive test would fail.