Clever little C# and ASP.NET Core features that make me happy

I recently needed to refactor my podcast site which is written in ASP.NET Core 2.2 and running in Azure. The Simplecast backed API changed in a few major ways from their v1 to a new redesigned v2, so there was a big backend change and that was a chance to tighten up the whole site.

As I was refactoring I made a few small notes of things that I liked about the site. A few were C# features that I'd forgotten about! C# is on version 8 but there were little happinesses in 6.0 and 7.0 that I hadn't incorporated into my own idiomatic view of the language.

This post is collecting a few things for myself, and you, if you like.

I've got a mapping between two collections of objects. There's a list of all Sponsors, ever. Then there's a mapping of shows where a show might have n sponsors.

Out Var

I have to "TryGetValue" because I can't be sure if there's a value for a show's ID. I wish there was a more compact way to do this (a language shortcut for TryGetValue, but that's another post).

Shows2Sponsor map = null;

shows2Sponsors.TryGetValue(showId, out map); 
if (map != null)
{ 
    var retVal = sponsors.Where(o => map.Sponsors.Contains(o.Id)).ToList();
    return retVal;
}
return null;

I forgot that in C# 7.0 they added "out var" parameters, so I don't need to declare the map or its type. Tighten it up a little and I've got this. The LINQ query there returns a List of sponsor details from the main list, using the IDs returned from the TryGetValue.

if (shows2Sponsors.TryGetValue(showId, out var map))
    return sponsors.Where(o => map.Sponsors.Contains(o.Id)).ToList();
return null;

Type aliases

I found myself building JSON types in C# that were using the "Newtonsoft.Json.JsonPropertyAttribute" but the name is too long. So I can do this:

using J = Newtonsoft.Json.JsonPropertyAttribute;

Which means I can do this:

[J("description")] 

public string Description { get; set; }


[J("long_description")]
public string LongDescription { get; set; }

LazyCache

I blogged about LazyCache before, and its challenges but I'm loving it. Here I have a GetShows() method that returns a List of Shows. It checks a cache first, and if it's empty, then it will call the Func that returns a List of Shows, and that Func is the thing that does the work of populating the cache. The cache lasts for about 8 hours. Works great.

public async Task<List<Show>> GetShows()

{    

    Func<Task<List<Show>>> showObjectFactory = () => PopulateShowsCache();

    return await _cache.GetOrAddAsync("shows", showObjectFactory, DateTimeOffset.Now.AddHours(8));

}

private async Task<List<Show>> PopulateShowsCache()

{

    List<Show> shows = shows = await _simpleCastClient.GetShows();

    _logger.LogInformation($"Loaded {shows.Count} shows");

    return shows.Where(c => c.Published == true && c.PublishedAt < DateTime.UtcNow).ToList();

}

What are some little things you're enjoying?

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