Database constraint names and hash collision

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

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