This is a dangerous, slippery slope. In .NET there are two and only two equality semantics: reference and value type.
Assuming that ibatis is now also checking .Equals as opposed to its previous reliance on only GetHashcode, the responsibility falls on the creator of the class being checked for equality, not on ibatis, to perform the appropriate comparison. Reference types that wish to use a value-type equality semantic must implement the appropriate method overrides themselves (as System.String does, for example). Ibatis must in turn use only .GetHashcode() and .Equals(...). Any other expected behaviour indicates that the class being compared has implemented the wrong equality semantic. Jeremy Gray -----Original Message----- From: Clinton Begin (JIRA) [mailto:[EMAIL PROTECTED] Sent: Monday, October 24, 2005 4:07 PM To: ibatis-dev@incubator.apache.org Subject: [jira] Reopened: (IBATISNET-118) CacheKey.Equals(object) override can return true when the parameters have the same HashCode but are not equal. [ http://issues.apache.org/jira/browse/IBATISNET-118?page=all ] Clinton Begin reopened IBATISNET-118: ------------------------------------- This is still an issue. The equals method is using hashcode exclusively to compare the values. It cannot, no matter what the hashcode algorithm is, 32 bits will never be enough to compare uniqueness. So.... The Equals method of the cachekey object should.... 1) use hashcode for each parameter to determine initial match (for performance) 2) double-check the using a true equals method that directly compares each parameter for exact equality. There is NO other way to do this. We had the same problem in Java, and it's a pretty serious bug...anything that ends up returning incorrect results from the DB is our highest priority. Let me know if you'd like an explanation of the sequence of events, problem and solution from the Java version. Cheers, Clinton > CacheKey.Equals(object) override can return true when the parameters have the same HashCode but are not equal. > ------------------------------------------------------------------------ -------------------------------------- > > Key: IBATISNET-118 > URL: http://issues.apache.org/jira/browse/IBATISNET-118 > Project: iBatis for .NET > Type: Bug > Components: DataMapper > Versions: DataMapper 1.2.1 > Environment: Windows > Reporter: Thomas Tannahill > Assignee: Gilles Bayon > Fix For: DataMapper 1.3 > > CacheKey.Equals(object) override can return true when the parameters have the same HashCode but are not equal. This can cause false cache hits. > Only an issue for complex parameters. > Failing NUnit test: > ---- UNIT TEST BEGIN ---- > using IBatisNet.DataMapper; > using IBatisNet.DataMapper.TypeHandlers; > using NUnit.Framework; > namespace IBatisNet.DataAccess > { > [TestFixture] > public class CacheKeyTests > { > private const long A_LONG = 1L; > private const long ANOTHER_LONG_WITH_SAME_HASHCODE = -9223372034707292159; > > public CacheKeyTests() > { > } > [Test] > public void ShouldNotBeConsideredEqualWhenParametersHaveTheSameHashCodeButAreNotEqua l() > { > TypeHandlerFactory factory = new TypeHandlerFactory(); > // Two cache keys are equal except for the parameter. > CacheKey key = new CacheKey(factory, "STATEMENT", "SQL", new TestClass(A_LONG), new string[] {"AProperty"}, 0, 0, CacheKeyType.Object); > CacheKey aDifferentKey = new CacheKey(factory, "STATEMENT", "SQL", new TestClass(ANOTHER_LONG_WITH_SAME_HASHCODE), new string[] {"AProperty"}, 0, 0, CacheKeyType.Object); > Assert.IsFalse(aDifferentKey.Equals(key)); // should not be equal. > } > } > public class TestClass > { > private long aProperty; > public TestClass(long aProperty) > { > this.aProperty = aProperty; > } > public long AProperty > { > get { return aProperty; } > set { aProperty = value; } > } > } > } > ---- UNIT TEST END ---- > The test passes if you replace this line in CacheKey.Equals(): > if (_hashCode != cacheKey._hashCode) return false; > with something like this: > if (this._parameter == null && cacheKey._parameter != null) return false; > if (this._parameter != null && cacheKey._parameter == null) return false; > if (!this._parameter.Equals(cacheKey._parameter)) return false; -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira
