Many providers allow direct entity comparisons, specifically these are:

.Where(e => e != null)

At the top level this is effectively .Where(true)

.Where(e => e == null)

At the top-level this effectively is .Where(false)

.Where(e => e == f)

At the top-level this is effectively key comparisons.  e.g. Where(e => e.Id == f.Id)

.Where(e => e != f)

At the top-level this is effectively key comparisons.  e.g. Where(e => e.Id != f.Id)

Solution

We should probably just match any direct comparisons to the key which will handle all these scenarios as well as odd ones like .Where(e => e > f) if EF doesn't prevent that.

Open questions

1. Do we want to support owned entity comparisons? They don't have real keys so we'd have to do full-property comparisons which would be different from the top-level comparisons here and may match multiple entities as there is no ref integrity.