Hello all,

namespace NHibernate.Mapping

{

...

public class Table : IRelationalModel

{

...

public string UniqueColumnString(IEnumerable iterator, string referencedEntityName)

{

                ...

return (name.GetHashCode().ToString("X") + result.GetHashCode().ToString("X")); // Ouch!

}

}

}

We’ve just hit a problem on this line where we have two constraints on the same table.

Because they’re on the same table, name is the same.

And we have found a hash collision on result, due to weakness in how result is being generated.

Adding hashes together for string hashes isn’t safe.

In our case,

"BluewireTechnologies.Core.Framework.DynamicTypes2.Albatross.ITestManyA".GetHashCode()+"itestmanyaid".GetHashCode()

Is equal to:

"BluewireTechnologies.Core.Framework.DynamicTypes2.Albatross.ITestManyB".GetHashCode()+"itestmanybid".GetHashCode()

On V2 runtime.

Changing this code would cause the schemas NHibernate generates to change :-(

How much of people’s code would this break? (I don’t use NHibernate in a very conventional way, so I’m not very familiar with this)

Is it worth submitting a patch, or are we going to have to live with the broken behaviour for backwards compatibility?

Alun Harford