C
C#•2d ago
C@NYON⭐ONL!NE

How to properly use IMemoryCache?

Hi, all: I'm working on improving latency for a Razor Page page load, which I can immediately do by caching query results. I've read this: https://www.learnrazorpages.com/razor-pages/caching, but I don't entirely understand how to: - Manage the lifetime of the cache disposable - Asynchronously get or create an entry As an example, I have the following: 
    public List<IndicatorDisplayExternal> IndicatorDisplays { get; set; } = [];
    private const string _indicatorDisplayKey = "IndicatorDisplays";
...
        IndicatorDisplays = await _memoryCache.GetOrCreateAsync(
            _indicatorDisplayKey,
            async entry => await _indicatorService.GetProblematicIndicatorDisplaysAsync()
        );
    public List<IndicatorDisplayExternal> IndicatorDisplays { get; set; } = [];
    private const string _indicatorDisplayKey = "IndicatorDisplays";
...
        IndicatorDisplays = await _memoryCache.GetOrCreateAsync(
            _indicatorDisplayKey,
            async entry => await _indicatorService.GetProblematicIndicatorDisplaysAsync()
        );
My main questions with this: - I didn't use a using statement like the page instructs with managing cache entries, is this okay? - The compiler is warning me of a possible null reference assignment, but how can GetOrCreateAsync return null if my GetProblematicIndicatorDisplaysAsync will never return null? Once I get this sorted I'd like to set the cache entry to expire after some time. Would that just look like: var options = new MemoryCacheEntryOptions().SetAbsoluteExpiration(DateTime.Now.AddMinutes(10)); Passing that as the last parameter of the GetorCreateAsync call (also, should options become a field of my class?). Any advice or warnings about using the IMemoryCache would be appreciated, thanks!
1 Reply
Sossenbinder
Sossenbinder•this hour
https://source.dot.net/#Microsoft.Extensions.Caching.Abstractions/MemoryCacheExtensions.cs,224 if you look at the implementation of the extension method you used, you can see that it wraps the entire CacheEntry disposal for you, so implicitly you're doing the wrong thing, but the surface API is just easier to use. For the nullability: It's perfectly valid to cache null on a key So even if you never intend to actually cache null, there's no rule which would keep you from doing it, so the memorycache methods also won't pretend that the value is always non-null If you know it's never going to be null you can always ! it For the entries, you can either pass them as a separate parameter and it will apply all of the options to the entry Or, within the second parameter callback, you can set the options on the entry directly So it's basically just a way to pass an entire options object if you have that stored for reuse somewhere

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