Incorrect hashcode caching in Entity

[CodesInChaos]

Entity caches the hash code on the first call to GetHashCode(). This is a bug because the properties from which the hashcode is calculated can change thus rendering the cached hashcode invalid and violation the combined contract of Equals and GetHashCode.

[alecwhittington]

feel free to fork, apply the fix, and issue a pull request

[geoffreysmith]

GetHashCode() uses the DomainSignature properties to calculate the HashCode(), "Since it is recommended that GetHashCode change infrequently, if at all, in an object's lifetime, it's important that properties are carefully selected which truly represent the signature of an object." I'm okay with it calling from a cache rather than calculating it each time, unless you had additional thoughts on the matter?

[geoffreysmith]

Okay it has been a week with no response, please feel free to send me a note and I'll open this back up for discussion.

[cbp123]

The implemented version of GetHashCode() causes problems when used across sessions. For example, consider the following test:

public void Test()
{
var foo = new Foo();

// Try uncommenting the next line
// foo.GetHashCode()

foo.Bars.Add(Session.Load<Bar>(55));

Session.Save(foo);

Session.Flush();
Session.Clear();

var reloadedFoo = Session.Load<Foo>(foo.Id);

Assert.That(foo.Bars.Contains(reloadedFoo));

}

This test can pass or it can fail.
It will pass if you leave the call to GetHashCode() line commented out. It will fail if you uncomment the line.

I can see why you have decided to cache the hashcode, but I find that it can be confusing and problematic.