ASP.NET Core – How to add your own action filter

Action filters allow you to look at requests right before they are routed to an action method (and responses right after they are returned from the action method). The simplest way to add your own action filter in ASP.NET Core is to subclass ActionFilterAttribute and then override the appropriate methods depending on if you want … Read more

C# – Add or overwrite a value in ConcurrentDictionary

The simplest way to add or overwrite a value in a ConcurrentDictionary is to use the indexer: If the key doesn’t exist, this adds it. If the key exists, this overwrites it. The indexer is thread-safe. The indexer is the simplest way to unconditionally add / overwrite a value. Sometimes you’ll want to use other … Read more

C# – How to use Polly to do retries

Whenever you’re dealing with code that can run into transient errors, it’s a good idea to implement retries. Transient errors, by definition, are temporary and subsequent attempts should succeed. When you retry with a delay, it means you think the the transient error will go away by itself after a short period of time. When … Read more

System.InvalidOperationException: Collection was modified; enumeration operation may not execute

If you try to add/remove items from a collection while it’s being looped over in a foreach loop (enumerated), then you’ll get the following exception: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.at System.Collections.Generic.List`1.Enumerator.MoveNext() This error can happen in two scenarios: You’re looping over the collection in a foreach loop and modifying it (add/removing) … Read more