SQL Session with simultaneous In-Memory Cache? about session

[davidfowl]

Session is always backed by an IDistributedCache implementation. IMemoryCache is a different interface completely. Are you asking if you can use 2 implementations of session within the same app or are you asking if you can configure session to use the SQL implementation of IDistributedCache and also use IMemoryCache for other things?

If it's the latter, then yes, because those are 2 different interfaces that becomes trivial.

[Tratcher]

Sounds like he wants IDistributedCache for session and IMemoryCache for other stuff. Yes, that's just fine. Go look at the cache repo samples.

[SimonOrdo]

Right, so the sample at https://github.com/aspnet/Session/blob/dev/samples/SessionSample/Startup.cs says to do something like this:

// Uncomment the following line to use the Microsoft SQL Server implementation of IDistributedCache.
        // Note that this would require setting up the session state database.
        //services.AddSqlServerCache(o =>
        //{
        //    o.ConnectionString = "Server=.;Database=ASPNET5SessionState;Trusted_Connection=True;";
        //    o.SchemaName = "dbo";
        //    o.TableName = "Sessions";
        //});

I'm probably completely misinterpreting this, but to me that implies that in order to have SQL backed sessions, I need to change caching to also use a SQL store.

I I have all three:

services.AddSqlServerCache(); // add SQL backed implementation of IDistributedCache ?
services.AddCaching(); // add IMemoryCache,IDistributedCache for general in-proc caching?
services.AddSession(); 

The sample implies that without line 1 AddSqlServerCache(), the call to AddSession() results in the use of the IMemoryCache added from the call to AddCaching()?

How does AddSession know to use the SQL IDistributedCache instead of the IMemoryCache?

Am I just completely confused about how any of this works? LOL!

[Tratcher]

Session always uses IDistributedCache
https://github.com/aspnet/Session/blob/dev/src/Microsoft.AspNet.Session/SessionServiceCollectionExtensions.cs#L27
https://github.com/aspnet/Session/blob/dev/src/Microsoft.AspNet.Session/DistributedSessionStore.cs#L16
AddCaching adds a IDistributedCache implemented using IMemoryCache:
https://github.com/aspnet/Caching/blob/dev/src/Microsoft.Extensions.Caching.Memory/MemoryCacheServicesExtensions.cs#L23
If you replace that IDistributedCache registration with AddSqlServerCache then you use SQL distributed cache, but IMemoryCache is still registered as a seperate service.

[SimonOrdo]

Oh, I see. So the order in which I register them is key to making this work? Specifically, for my scenario it needs to be:

AddCaching(); // Add IMemoryCache and IDistributedCache
AddSqlServerCache(); // overwrite IDistributedCache registration from AddCaching with SQL backing
AddSession(); // which will now resolve to using SQL backed IDistributedCache

Is that about right?

[Tratcher]

Yes, that should work.

[SimonOrdo]

Phew! Thank for your time! I appreciate the help.

As a side note, it would be cool if the "AddServiceX" extension methods had some easy way to see what services they register without having to find the source (maybe in the method comments).