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NHibernate asks .NET to convert a string parameter to an integer, don't know why

Answer 1

+1 A:

For starters, you are mapping the ID columns twice: as a reference, and as part of a composite-id.

This is wrong, you should use the fluent equivalent of <key-many-to-one/> to map the id members.

But there's more... if this class doesn't have any data, why map it at all?

If would be better to have a Set of Staff in Class and vice-versa (mapped as many-to-many).

I'll assume your query is to the the Students for a "Staff".

Model:

public class Student : Entity<Guid>
{
}

public class Staff : Entity<Guid>
{
}

public class Class : Entity<Guid>
{
    public virtual ICollection<Student> Students { get; set; }
    public virtual ICollection<Staff> Staff { get; set; }
}

Mapping is just many-to-many on those collections, so I'll leave it out.

And query is a lot easier to do with HQL than Criteria:

var students = session.CreateQuery("see the query below")
                      .SetParameter("staff", id)
                      .List<Student>();

from Student s
where s in
        (select elements(c.Students)
         from Class c
         where :staff in elements(c.Staff))

Diego Mijelshon 2010-07-13 18:23:09

Thank you for your answer.I don't see how to do the desired SQL statement without adding the join table as an explicit entity (cf. http://stackoverflow.com/questions/1047895/nhibernate-query-filtering-on-a-list-of-values-using-criteria).I have removed the extra references (which were merely a convenience) and it does not change anything. I should mention this is a legacy database so options such as adding a surrogate key instead of the composite key are not an option.

MikeBaz 2010-07-13 18:31:34

The many-to-many exists in the appropriate domain objects. That doesn't tell me what's wrong here, though.

MikeBaz 2010-07-13 18:52:26

It looks like you are trying to use NHibernate like a Dataset, mapping based on columns. I'll try to add some better-looking code to the answer.

Diego Mijelshon 2010-07-13 19:13:51

Class actually has the mappings you show already for the student and staff references, and that is working without incident. I need to be able to alter the query at runtime, and it seemed that Criteria API was the right way to do that - otherwise I'd have to parse the HQL which I didn't want to do.

MikeBaz 2010-07-13 19:26:59

Answer 2

A:

Just to close this question off - I gave up on convincing NHibernate to do what I wanted. I decided instead to use General SQL Parser and a wrapper around the real command and connection providers. A similar task for a different reason is described at http://blog.theagileworkshop.com/2009/06/09/using-schemas-with-sqlite-for-in-memory-nhibernate-tests/. In any event, this avoids the whole issue because it forces me to work at the SQL level, which ot only lets me do what I want without NHibernate getting in the way but also allows HQL and even direct DB access to be intercepted.

MikeBaz 2010-07-21 13:24:44

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NHibernate asks .NET to convert a string parameter to an integer, don't know why

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