Merge pull request #129 from benmccallum/patch-1

Add note about sync-over-async

Author: koenbeuk

README.md

@@ -214,6 +214,9 @@ In this example we were not able to inherit from TriggeredDbContext since we wan
 ### Custom trigger types
 By default we offer 3 trigger types: `IBeforeSaveTrigger`, `IAfterSaveTrigger` and `IAfterSaveFailedTrigger`. These will cover most cases. In addition we offer `IRaiseBeforeCommitTrigger` and `IRaiseAfterCommitTrigger` as an extension to further enhance your control of when triggers should run. We also offer support for custom triggers. Let's say we want to react to specific events happening in your context. We can do so by creating a new interface `IThisThingJustHappenedTrigger` and implementing an extension method for `ITriggerSession` to invoke triggers of that type. Please take a look at how [Transactional triggers](https://github.com/koenbeuk/EntityFrameworkCore.Triggered/tree/master/src/EntityFrameworkCore.Triggered.Transactions) are implemented as an example.
 
+### Async triggers
+Async triggers are fully supported, though you should be aware that if they are fired as a result of a call to the synchronous `SaveChanges` on your DbContext, the triggers will be invoked and the results waited for by blocking the caller thread as discussed [here](https://github.com/koenbeuk/EntityFrameworkCore.Triggered/issues/127). This is known as the sync-over-async problem which can result in deadlocks. It's recommended to use `SaveChangesAsync` to avoid the potential for deadlocks, which is also best practice anyway for an operation that involves network/file access as is the case with an EF Core read/write to the database.
+
 ### Similar products
 - [Ramses](https://github.com/JValck/Ramses): Lifecycle hooks for EF Core. A simple yet effective way of reacting to changes. Great for situations where you simply want to make sure that a property is set before saving to the database. Limited though in features as there is no dependency injection, no async support, no extensibility model and lifecycle hooks need to be implemented on the entity type itself.
 - [EntityFramework.Triggers](https://github.com/NickStrupat/EntityFramework.Triggers). Add triggers to your entities with insert, update, and delete events. There are three events for each: before, after, and upon failure. A fine alternative to EntityFrameworkCore.Triggered. It has been around for some time and has support for EF6 and boast a decent community. There are plenty of trigger types to opt into including the option to cancel SaveChanges from within a trigger. A big drawback however is that it does not support cascading triggers so that triggers can never be relied on to enforce a domain constraint.