How to use Azure Cache for Redis in a .NET Core web app

If you need a distributed cache and are planning on deploying your .NET Core web app to Azure, using Azure Cache for Redis as your cache provider is a good choice.

The steps below show you how to get started…

Create an Azure Cache for Redis instance using the portal

Search for ‘azure cache for redis’ on the portal and on the create screen fill in details such as resource group, DNS name, location and cache type.

Choose the same location as whatever app will be consuming your cache to minimise latency. When you’re just getting setup I’d recommend choosing the Basic C0 cache as this is the cheapest and you can always upgrade later. For all the other tabs just accept the defaults for the moment.

Create a new Redis cache in the portal

After Azure has finished creating your new cache, navigate into it and go to the Access keys page as shown below.

Copy the primary connection string somewhere as you’ll need to put this into your appsettings.json file in the next step.

Viewing Azure Redis access keys

Setup and configure your app

Install Microsoft.Extensions.Caching.StackExchangeRedis from NuGet.

Amend Startup.cs…

Amend startup.cs to use caching

Add a connection string pointing to your Redis instance on Azure into your appsettings.json file. Remember you can get this from the Access keys page as shown above. In our real apps we’d likely store this value in Azure Key Vault.

appsetting-redis-cache

Create a cache wrapper or helper class

At this stage your app should be able to set and read items in Azure Redis by instantiating a concrete instance of the IDistributedCache instance. The next step is to create a simple thin wrapper around this interface. It’s not 100% needed but it helps keep code that is using the cache a little bit neater.

Since .NET Core 3.0 Microsofts default JSON deserializer has been System.Text.Json, however it doesn’t support circular references so in the below example I’ve fallen back to using Newtonsoft.

Note… according to Microsoft System.Text.Json will support circular references from .NET 6.0.

Cache wrapper

Inject IDistributedCache into your controller or service class

Since dependency injection is built into .NET Core and because we’ve registered the Redis Cache service in our Startup.cs file we can inject an instance of the IDistributedCache into our controller class…

Inject IDistributedCache

Check the cache when retrieving data

Finally to use the cache when getting data… we can implement the cache-aside pattern. In this pattern we…

First check the cache for a particular key.
If it does not exist we read data from the DB and store it in the cache.
If it does exist in cache we use the cached version of the data.

Below I’m checking the cache for a list of products…

Example of cache-aside pattern

In this case I’ve not set any DistributedCacheEntryOptions meaning items will not expire. If you need to set absolute or sliding expirations on items you can set the relevant options when adding them to the cache.

Remove items from cache after they’ve been updated

When some data change occurs which means previously cached items are now stale we can remove items from the cache as below…

Invalidate items in cache by removing them

In this case the list of products I previously cached is no longer valid as I’ve deleted one of them.

Depending on the situation we might not have to explicitly remove certain items from the cache like above. In many cases some staleness is acceptable so in this case we might set a sliding expiration of 1 hour or depending on the data just re-cache certain items overnight.

How to test your app is storing items in and reading from Azure Cache for Redis

To confirm everything is working as expected we can run the monitor command in the Redis console direct on the Azure portal.

Override the default controller scaffold templates in Visual Studio 2019 and .NET 5.0

The real power of scaffolding in Visual Studio comes from the ability to override the templates which are used to generate the controllers and views. This gives us complete control of the C# and HTML which is emitted by the scaffolding process.

The templates for Visual Studio 2019 and .NET 5.0 are stored in C:\Users\USERNAME\.nuget\packages\microsoft.visualstudio.web.codegenerators.mvc\5.0.2 as shown below…

Where to find scaffold templates

We can update these templates directly in the above location but this is problematic as it is local to a developers machine and therefore not easily shared with other team members and because changes made here would affect all projects on the machine which may not be desired.

A better way is to copy the templates into our MVC projects like below so they can be checked into source control and shared across the team.

Required folder structure for custom scaffolding

This works as by convention Visual Studio will look for a Templates folder in the MVC project first before using the machine level folder.

Note… you may see build errors related to the templates you’ve just copied into your project before you first try to scaffold. These will go away when Microsoft.VisualStudio.Web.CodeGeneration.Design is installed which Visual Studio will do as part of the scaffold process.

Scaffolding multiple controllers at once from the command line

After you’ve customised your templates you can rescaffold your controllers one by one manually from the GUI, but a better way is to call the asp.net core scaffolding engine from a bat file.

Enabling view refresh after .CSHTML changes for new projects in Visual Studio

Since .NET Core 3.0 your views in MVC won’t refresh after you change your .CSHTML markup. You can enable this for existing projects by installing Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation and setting AddRazorRuntimeCompilation() in your Startup.cs -> ConfigureServices method…

… and …

for new projects you can check the ‘Enable Razor runtime compilation’ checkbox for 3.1 projects onwards when creating the projects.

Enable view refresh for new projects in Visual Studio

Opening web apps in Incognito mode from Visual Studio

If you’re working on a web app in Visual Studio and want to launch it in Incognito mode to make sure you have a 100% reset state you can do this from the ‘Browse With…’ option which is next to the run button. From here you can add a browser with any supported launch switches you desire such as ‘–incognito’ (shown below) or perhaps ‘–disable-extensions’ to speed browser load time up.

We can see on Chromium based browsers that there is a lot of command line switches available and of course they can be combined.

Opening web apps in Incognito mode

Using ToLower() or ToUpper() in C# to compare strings is not safe in all cultures

If you’re using Resharper, Roslynator or similar you’ll likely see string comparisons using ToLower() or ToUpper() flagged.

Why?

Well these comparisons are not safe in all cultures. The canonical example is the ‘Turkish i problem‘ which relates to how in Turkish the dot is present on the top of the uppercase version of ‘i’ and there is no dot on the lowercase version of the ‘i’. This means using .ToLower() etc. may return different results on machines with different culture settings.

On their Best practices for comparing strings in .NET page Microsoft recommends using StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase for comparisons as your safe default for culture-agnostic string matching.

StringCompare example in C#

Aside from safe comparisons, StringComparison also expresses intent more clearly and does not need to create strings so there’s a potential performance boost too.