Equals / GetHashCode inconsistent in Identity object
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Description
Hi,
is there a reason why when pre-computing hashCode in Identity, otherTypes parameter is included but when comparing to other in Equals, it is not included?
https://github.com/StackExchange/Dapper/blob/master/Dapper/SqlMapper.Identity.cs
AFAIK, when two object equal, they should have the same hashcode, but if two identity objects were created with different otherTypes parameter, they won't.
We are occasionally seeing a production exception coming from multimap caused by an incorrect type cast. We think it might be caused by the same sql query used in MultiMap with different generic parameters where a deserializer cached for type X is returned for a different type Y. But we can't reproduce it reliably though.
Update: we linked our project to dapper source code for another round of debugging and now we are pretty sure our issue is caused by the Equals/GetHashCode inconsistency.
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Research direction
Start with Dapper/SqlMapper.Identity.cs and trace Identity.Equals alongside the precomputed GetHashCode, focusing on the otherTypes parameter. Then inspect the identity cache and MultiMap path for a regression case involving different generic parameters; done means equal identities produce matching hashes and the incorrect deserializer cast is no longer observed.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- csharp
- Domain
- databases
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100