Problem statement:

The IDistributedCache API is very minimal, requiring a lot of boilerplate code to check for values, get missing values, serialize, deserialize, etc; this makes actually using the cache overly complex.

The purpose of this example is to show helper APIs for using IDistributedCache, so that callers can reuse common code for the caching aspects, and focus on the things that impact them:

• what the key is (specified only once)
• where the data should come from if it isn't available
• what the expiration options should be

Helper extension methods are provided in DistributedCacheExtensions that allow sync and async callbacks (to fetch missing data), optionally allowing the TState pattern (often associated with static lambdas in high throughput scenarios - in many real-world scenarios, the TState pattern can be overlooked with the simpler captured variables / non-static lambda approach.

The topic of serialization is discussed, with the example using System.Text.Json to avoid requiring external dependencies; however, other serializers are available with a range of different performance characteristics and feature sets.

Four routes are configured, using minimal APIs:

• /sync uses a synchronous simple lambda
• /async uses an asynchronous simple lambda
• /{foo}/{bar}/sync uses a synchronous static/TState lambda, also showing key-partitioning
• /{foo}/{bar}/async uses an asynchronous static/TState lambda, also showing key-partitioning

Each of these routes simply caches the current time, with a 30 second expiration; hitting the same route in that interval should show the same time, before updating. It uses the in-memory cache implementation, but other distributed cache stores are available.