January 27, 2025
I'm doing dotnet development for eight years, but just today I finally realised, what is the difference between .Find(..) and .Where(..):
When Where always makes request to database, Find looks first by id in already cached entities and only if not found, checks in database.
I must have read about it previously, but only today I have found that one particularly big chunk of a very important command works accidentally correctly because of that: we make a very big loop, in each iteration we create new entity with id from external source and saving to database happen only afterwards. Would we have used Where, entries would be duplicated (and exception thrown), but with Find it's possible to get cached version, that was not yet saved to database.
Here is small example that demonstrates what I mean:
public record Person(int Id, string Name);
using var db = new AppDbContext(); db.Database.EnsureCreated(); db.Peoples.Add(new Person(60, "John")); db.Peoples.FirstOrDefault(p => p.Id == 60); // will return null var jackByFind = db.Peoples.Find(60); // will return entity
It is also possible to make query to cache using DbSet<T>.Local.Where(..), but afaik there is no straightforward way to make complex query by non-key parameters to cached version and, if not found - to database.