bug in select max of string in linq to nhibernate

If you can submit the code within a few days it should be present in the 3.3.3 release.

In the meantime, you can use the same code with an official 3.3.2 build by just subclassing from DefaultLinqToHqlGeneratorsRegistry to add the registration and set the configuration property linqtohql.generatorsregistry to its assembly qualified name. (Or in you can use the Loquacious-configuration LinqToHqlGeneratorsRegistry<MyLinqToHqlGeneratorsRegistry>()

Rather than spend time on a workaround, I think the quickest solution for you would be to simply add the support for ToInt32 and similar. I don't think it should be very difficult.

See for instance for some example:
https://github.com/nhibernate/nhibernate-core/blob/master/src/NHibernate/Linq/Functions/MathGenerator.cs
The treeBuilder variable at the bottom has a Cast() method to output the corresponding HQL

Then it's need to be registered in
https://github.com/nhibernate/nhibernate-core/blob/master/src/NHibernate/Linq/Functions/DefaultLinqToHqlGeneratorsRegistry.cs

By cast to nullable int , this problem is resolved. So my problem is other thing. My purpose of use to Parse() or ToInt32(), for this that cast string to int Before Max(). Is there another solution for my problem?

my expect query is :

select
max(cast(product0_.QuantityPerUnit as INT) as col_0_0_)
from
Products product0_

For clarity, closing as not an issue - Max() over strings works correctly.

For supporting Parse() and ToInt32() etc, I've opened NH-3377.

Supporting these methods shouldn't be too difficult (inherit from BaseHqlGeneratorForMethod). Wanna have a go at creating a pull request to fix NH-3377?

string comparing works different way than numbers. If you will run your original query with linq-2-objects you will get the same result ("900" but not "80001")