Entity framework: Different connection issues occurring occasionally

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votes

In the last few days, we are recording different exceptions thrown by entity framework (version 6) on our live stage, which only occur occasionally and show error messages, which all relate to the database connection.

  • Not allowed to change the 'ConnectionString' property. The connection's current state is closed.

  • The context cannot be used while the model is being created. This exception may be thrown if the context is used inside the OnModelCreating method or if the same context instance is accessed by multiple threads concurrently. Note that instance members of DbContext and related classes are not guaranteed to be thread safe.

  • Unexpected connection state. When using a wrapping provider ensure that the StateChange event is implemented on the wrapped DbConnection.

  • The underlying provider failed on Open.

We can not remember that we've changed anything and as already said these errors occur only sometimes. We can not reproduce them on local stage.

Does anyone have an idea what is going wrong or how to investigate?

Edit: It is an ASP.NET MVC 5 application which uses Unity IoC for instantiation. We use a self-written PerRequestLifeTimeManager which runs absolutely smooth in other mvc applications.

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c#asp.net-mvcentity-frameworkentity-framework-6
Can you share the piece of code where you are seeing this error? Were you able to identify any pattern or use case during which the error pops up? Do you have any application logs which can tell at which line of code the exception is thrown? - Chetan
I'm pretty sure that you're using contexts the wrong way. Probably as static members, but surely in a way that they're accessible by multiple threads. Refactoring time! - Gert Arnold
It's impossible to say without code. However, I would tend to agree with @GertArnold. You should have one and only one context instance per request. If you're newing up multiple instances per request or, conversely, using it statically or as a singleton, etc. you're going to have issues. - Chris Pratt
I don't think it makes sense to share code because there are hundreds of lines where we access the database ;) Thanks for the hint regarding database contexts shared accross requests. Actually we use a PerRequestLifetimeManager in Unity IoC but maybe there is an instantiation issue before or after the execution of the mvc action. - krani

1 Answers

2
votes

Thanks to the hint of @Gerd Arnold and @Chris Pratt I was able to figure out the root-cause of my issue.

Indeed the exceptions where caused by an instance of DbContext which was used concurrently accross multiple requests. This DbContext is part of an service which is injected by Unity property injection into an action filter. What I didn't know yet is that action filters don't get instantiated per request in APS.NET MVC but they are cached and reused. So do not inject instances of DbContext or DbContext-based classes into action filters!

We solved that issue by calling DependencyResolver.Current.GetService<ClassType>() instead of using Dependency-attribute in our filter's code to get an instance of the respective dependency (Please note that you lose the testability of the filter through this workaround)

It took me many hours to find the solution. To those users who occasionally encounter the same errors as mentioned in my question I would recommend check your appliation for any DbContext-based classes which might get used concurrently accross requests/threads.

  1. Check your Unity IoC rules
  2. Look for classes which do not get instantiated through IoC but might be used concurrently.
  3. Check all steps along the MVC request lifecycle