ASP.NET Core › Caching

How would you cache the results of an expensive, paginated database query while correctly handling different page/filter parameter combinations?

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Answer

Include all parameters that affect the query's result set (page number, page size, sort order, filter values) as part of the cache key, since caching under a key that ignores a parameter would return the wrong page/filtered results to a subsequent request with different parameters -- Output Caching's VaryByQueryKeys handles this declaratively for HTTP-level caching, while application-level caching requires manually composing a sufficiently unique key string.

// Application-level: composite key including all relevant parameters
var cacheKey = $"products-page{page}-size{pageSize}-sort{sortBy}-category{category}";

// Output Caching: declarative equivalent
[HttpGet]
[OutputCache(VaryByQueryKeys = new[] { "page", "pageSize", "sortBy", "category" })]
public IActionResult GetProducts(int page, int pageSize, string sortBy, string category) { ... }

Real-world example A bug where users saw identical results regardless of their selected sort order was traced to a cache key that only included the page number, not the sortBy parameter, causing the first-cached sort order to be returned for every subsequent request.

Common follow-ups: What happens if you forget to include a parameter that affects the query in the cache key?;How does an overly granular cache key (too many parameter combinations) hurt cache hit rate?

Entity Framework Core & Data Access;ASP.NET Core Middleware & Request Pipeline