IdentityMap throws when records are loaded & modified.

[Hawxy]

When using an identity map, it will throw when records that have been previously loaded are modified & stored, as the record will not meet the reference equality check.

       ProjectAsync<MyEntityEdited>(async (edited, operations) =>
        {
            var entities = await operations.LoadManyAsync<MyEntity>(created.IdList);

            var updatedEntities = entities.Select(x => x with { SomeId = edited.Id }).ToArray();
            operations.Store(updatedEntities);
        });

System.InvalidOperationException
Document 'MyEntity' with same Id already added to the session.
   at Marten.Internal.Storage.IdentityMapDocumentStorage`2.store(IMartenSession session, T document, TId& id)
   at Marten.Internal.Storage.IdentityMapDocumentStorage`2.Store(IMartenSession session, T document)
   at Marten.Internal.Sessions.DocumentSessionBase.storeEntity[T](T entity, IDocumentStorage`1 storage)
   at Marten.Internal.Sessions.DocumentSessionBase.store[T](IEnumerable`1 entities)
   at Marten.Internal.Sessions.DocumentSessionBase.Store[T](T[] entities)

Relevant part of the identity map:

marten/src/Marten/Internal/Storage/IdentityMapDocumentStorage.cs

Line 53 in 6459822

if (!ReferenceEquals(existing, document))

[Hawxy]

@jeremydmiller I've fixed this locally by checking if the type implements IEquatable<T> and skipping the equality check if it does. Can push it up if you're fine with that as a solution.

[jeremydmiller]

I'm good with that, go for it