Wrong mapping when using long Id

[manuel-ornato]

Hi,

Great lib overall, thanks for sharing your work.

I have a mapping issue when using long Ids.

Here is a short console app sample that reproduces the problem: longIdsIssue.cs.

I create 4 dynamic Expandos with distincts long Ids. There is a child table Id (int) too.
As you see all Ids (parents and children) are distincts, so in the end we should have 4 distinct instances of the parent class, each one being linked to a distinct instance of the child class.

Instead, the mapping results in only 2 instances of the parent class, one containing 3 children and the other containing the last child.

The problem goes away if I change Ids to int.

Manuel

[manuel-ornato]

Hi,

I found the culprit in GetIdentifierHash (InternalHelpers.cs):

unchecked
{
    // Include identifier hashcode to avoid collisions between e.g. multiple int IDs
    identifierHash += identifierValue.GetHashCode() + identifier.GetHashCode();
}

One can't rely on GetHashCode() to uniquely identify a long. Actually one can't rely on an hash code to uniquely identify anything... It's just a hash, not a key.

Colllisions will happen and well... they did. In the sample I provided, 3 of my 4 long values have the same hash code. In my real database there are more than 1000 collisions actually.

I guess the fix would be to maintain your own hastable collision mecanism. That is ìnstanceCache should be a Dictionary<Tuple<int, int, object>, ICollection<object>>() and then you would have to compare the real identifiers before returning an instance.

Hope this helps.

Manuel

[manuel-ornato]

I submitted PR #49 to fix this.
Just changed the Cache Key to compare identifiers whole values and not their hashcodes.

[odelvalle]

Fixed. Pull request #49 merged in master