Discussion on: C# and .NET Core Appreciation Post. The most beautiful piece of code I have ever seen... this month!

[Ken in NH]

I will add my voice to the others here who recommend avoiding LINQ syntax. Most MS development shops have gotten away from LINQ syntax and your query shows one good reason:

It might be more efficient for the where to execute before the join. With the LINQ syntax you can do it but it looks odd.

var user = (from t in _context.Tokens
    where t.Body == token
    join u in _context.Users
        on t.UserId equals u.Id
    select u).SingleOrDefault();

Now compare:

var user = _context
    .Tokens
    .Where(t => t.Body == token)
    .Join(
        _context.Users,
        t => t.UserId,
        u => u.Id,
        (t, u) => u)
    .SingleOrDefault();

For your specific case, I suggest you turn _context.Tokens into an IDictionary<string, Token> or even IDictionary<string, User> where the token body is the key. Then your method looks like this:

#nullable disable
private User GetUserByToken(string token)
    => _context.UsersByToken.TryGetValue(token, out var user)
    ? user
    : default;
#nullable restore

[Sdu]

I have a question with this one. How would my DBContext class look like, will this UsersByToken field have to be mapped to a table in the bd too?

One thing that has been mentioned a couple of times is that I should consider using IDictionary, I'm looking forward to it

[Ken in NH]

Ah. I did not know what _context was and I was not aware you were using EF. I assumed _context was some kind of property bag or class you controlled. So, the answer is no you would not have a UsersByToken property on your DbContext and it would not map to the database. Instead it should be a local field/property in your login class. Now that I understand you are making round trips to the database, you will find IDictionary<> to be even more efficient than your current code, but you will need a fall back to retrieving the user from the database if it is not found associated the provided token in your dictionary.

[Sdu]

Thank you for this. Seems like IDictionary and IQueryable are my best bet for getting the most out of EF