Creating a custom ConfigurationProvider for a Entity Framework Core source
ASP.NET Core has a lightweight configuration system that is designed to be highly extensible. It lets you aggregate many configuration values from multiple different sources, and then access those in a strongly typed fashion using the Options
pattern.
Using packages in the Microsoft.Extensions.Configuration
namespace, you can read configuration from:
- Azure Key Vault
- Azure App Configuration
- Command-line arguments
- Custom providers (installed or created)
- Directory files
- Environment variables
- In-memory .NET objects
- Settings files
For PineBlog I wanted some values that can be set in the appsettings.json
to be set from the admin UI as well. These values are stored in the database and exposed through a Entity Framework Core (EF Core) DbContext
.
In this post I'm going to describe creating a custom configuration provider that uses EF Core. For the sake of simplicity it is a more general description than the implementation in PineBlog.
Default configuration
Web apps based on the ASP.NET Core dotnet new
templates call CreateDefaultBuilder when building a host. This provides default configuration for the app, for instance the appsettings.json
using the File Configuration Provider. For more information see the official documentation on this topic.
public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>();;
The ConfigOptions
In this example we will have a ConfigOptions
class that maps to the configuration in appsettings.json
. And a ConfigEntity
class that overrides some of those configuration values from the database.
public class ConfigOptions
{
public string BackgroundColor { get; set; }
public int ItemsPerPage { get; set; }
public bool ShowHeader { get; set; }
// this property will not be overridden by ConfigEntity
public string ApiKey { get; set; }
}
public class ConfigEntity
{
public string BackgroundColor { get; set; }
public int ItemsPerPage { get; set; }
public bool ShowHeader { get; set; }
}
The appsettings.json
look like this:
{
"ConfigOptions": {
"BackgroundColor": "#ff0000",
"ItemsPerPage": 2,
"ShowHeader": true,
"ApiKey": "h&Ww1vbFP6y2RW7Nx$$Q&&KW"
}
}
Creating a custom configuration provider
With the basics out of the way, we can now start creating our custom configuration provider.
In order to create a custom provider, you need to implement the IConfigurationProvider
and IConfigurationSource
interfaces from the Microsoft.Extensions.Configuration.Abstractions
package. Or you can use any of the provided base classes to get started.
Configuration source
The IConfigurationSource
interface only has one method that needs implementing.
And because we will be using EF Core as a configuration source we need a DbContextOptionsBuilder
action to use the DbContext
from the configuration provider. We also have a ReloadDelay
to avoid triggering a reload before a change is completely saved.
public class ConfigEntityConfigurationSource : IConfigurationSource
{
public Action<DbContextOptionsBuilder> OptionsAction { get; set; }
public bool ReloadOnChange { get; set; }
// Number of milliseconds that reload will wait before calling Load. This helps avoid triggering a reload before a change is completely saved. Default is 500.
public int ReloadDelay { get; set; } = 500;
public IConfigurationProvider Build(IConfigurationBuilder builder)
{
return new ConfigEntityConfigurationProvider(this);
}
}
Configuration provider
For our custom configuration provider we use the ConfigurationProvider
base class, this is the most basic implementation of IConfigurationProvider
. The configuration provider initializes the database when it's empty.
We override the Load
method with our custom implementation, this method loads (or reloads) the data for the provider. Here we instantiate the DbContext
using the OptionsAction
from the configuration source. And we then get a ConfigEntity
from the database and set its values to the configuration dictionary of the configuration provider.
And by using the same keys for the configuration values (e.g. ConfigOptions.BackgroundColor
) as we used in the appsettings.json
we will effectively override those values with the values from the database.
public class ConfigEntityConfigurationProvider : ConfigurationProvider
{
private readonly ConfigEntityConfigurationSource _source;
public ConfigEntityConfigurationProvider(ConfigEntityConfigurationSource source)
{
_source = source;
}
public override void Load()
{
var builder = new DbContextOptionsBuilder<EntityDbContext>();
_source.OptionsAction(builder);
using (var context = new CustomDbContext(builder.Options))
{
context.Database.EnsureCreated();
var config = context.ConfigEntity.SingleOrDefault();
if (config == null) return;
Data = new Dictionary<string, string>();
Data.Add($"{nameof(ConfigOptions)}.{nameof(ConfigOptions.BackgroundColor)}", config.BackgroundColor);
Data.Add($"{nameof(ConfigOptions)}.{nameof(ConfigOptions.ItemsPerPage)}", config.ItemsPerPage);
Data.Add($"{nameof(ConfigOptions)}.{nameof(ConfigOptions.ShowHeader)}", config.ShowHeader);
}
}
}
We now have a configuration provider that loads its values from the database. But it will only do this once, when the application is started, and we want it to reload as well when the user updates the ConfigEntity
in the database.
Reloading configuration on entity changes
To trigger a reload of the configuration when the ConfigEntity
in the database changes, we need to let the configuration provider know that the entity has changed. We'll solve this by triggering an event on a entity change observer class and listening for this event in our configuration provider.
Entity change observer
We create a singleton class that has an EventHandler
for the entity changes. Our configuration provider can listen for this event to update the configuration.
I've made this class an old school singleton, since injecting it into the DbContext
was a bit complicated. And we use ThreadPool.QueueUserWorkItem
offload the invoking of the event to a background thread, so it doesn't block the DbContext.SaveChanges
.
public class EntityChangeObserver
{
public event EventHandler<EntityChangeEventArgs> Changed;
public void OnChanged(EntityChangeEventArgs e)
{
ThreadPool.QueueUserWorkItem((_) => Changed?.Invoke(this, e));
}
#region singleton
private static readonly Lazy<EntityChangeObserver> lazy = new Lazy<EntityChangeObserver>(() => new EntityChangeObserver());
private EntityChangeObserver() { }
public static EntityChangeObserver Instance => lazy.Value;
#endregion singleton
}
Notify the observer
Create a custom (base) class that extends DbContext
, and override the SaveChanges
methods.
public abstract class EntityDbContext : DbContext
{
public override int SaveChanges()
{
OnEntityChange();
base.SaveChanges()
}
public override async Task<int> SaveChangesAsync(CancellationToken cancellationToken)
{
OnEntityChange();
return await base.SaveChangesAsync(cancellationToken);
}
private void OnEntityChange()
{
foreach(var entry in ChangeTracker.Entries()
.Where(i => i.State == EntityState.Modified || i.State == EntityState.Added))
{
EntityChangeObserver.Instance.OnChanged(new EntityChangeEventArgs(entry));
}
}
}
Trigger a reload
To let the configuration provider know the entity has changed and to trigger a reload, we need to listen for the EntityChangeObserver.Changed
event. And because we only want to reload when the ConfigEntity
changes, we add a check to see if that is the type of the changed entity.
public ConfigEntityConfigurationProvider(ConfigEntityConfigurationSource source)
{
_source = source;
if (_source.ReloadOnChange)
EntityChangeObserver.Instance.Changed += EntityChangeObserver_Changed;
}
private void EntityChangeObserver_Changed(object sender, EntityChangeEventArgs e)
{
if (e.Entry.Entity.GetType() != typeof(ConfigEntity))
return;
Thread.Sleep(_source.ReloadDelay);
Load();
}
Add the configuration in the application
And finally in the Program.cs
we can now configure the IConfigurationSource
.
WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>()
.ConfigureAppConfiguration((hostingContext, config) => {
config.Add(new ConfigEntityConfigurationSource {
OptionsAction = o => o.UseInMemoryDatabase("db", new InMemoryDatabaseRoot()),
ReloadOnChange = true
});
});
Our application will now load the ConfigOptions
from the appsettings.json
, then use the ConfigEntityConfigurationSource
to override some of the values (when present in the database). And when the user updates the ConfigEntity
in the database the values will be reloaded.
Note: Use IOptionsSnapshot
to support reloading options with minimal processing overhead. Options are computed once per request when accessed and cached for the lifetime of the request. See the official documentation on reload configuration data with IOptionsSnapshot.
HttpExceptions updated for .NET Core 3.0
HttpExceptions has been updated to version 2.3 for use with the new .NET Core 3.0.
HttpExceptions?
HttpExceptions lets you return exceptions over HTTP e.g. as ASP.NET Core Problem Details, and has HTTP-specific exception classes that enable ASP.NET to generate exception information.
Getting started
In ASP.NET Core 3.0 you add the HttpExceptions services and the middleware in the Startup.cs
of your application. The change from 2.x to 3.0 is that you now add it to AddControllers()
instead of to AddMvcCore()
.
public void ConfigureServices(IServiceCollection services)
{
...
services.AddControllers().AddHttpExceptions();
...
}
Then you can add the HttpExceptions middleware using the application builder. UseHttpExceptions
should be the first middleware
component added to the pipeline. That way the UseHttpExceptions
Middleware catches any exceptions that occur in later calls. When
using HttpExceptions you don't need to use UseExceptionHandler
or UseDeveloperExceptionPage
.
public void Configure(IApplicationBuilder app)
{
app.UseHttpExceptions(); // this is the first middleware component added to the pipeline
...
}
InvalidModelStateResponseFactory API behavior
From this release on HttpExceptions always overrides the default Microsoft.AspNetCore.Mvc.ApiBehaviorOptions.InvalidModelStateResponseFactory
and related settings and
will use the configured ExceptionMappers. The SuppressInvalidModelStateResponseFactoryOverride
has been removed.
Where can I get it?
The code can be found on GitHub at: github.com/ofpinewood/http-exceptions. And there is also a sample project you can have a look at.
You can install the Opw.HttpExceptions and Opw.HttpExceptions.AspNetCore NuGet packages from the package manager console:
PM> Install-Package Opw.HttpExceptions
PM> Install-Package Opw.HttpExceptions.AspNetCore
Introducing PineBlog a new ASP.NET Core blogging engine

Why another blogging engine?
I've had a blog website for years (I do still need to move the old posts to this blog), and have been using various blogging engines. But I had some time lately and wanted to try some new things, so I thought lets build my own! When I started I knew there were a few things that I really wanted it to be/have:
- Super easy installation, basically add a NuGet package and done
- Modern architecture, I chose to use a Clean Architecture (youtube: Clean Architecture with ASP.NET Core)
- Light-weight, just a blogging engine nothing more..
- Write my posts in Markdown
So that is what I've been building :) So if you want to know more about it, please read on..
And I will write a more in depth blog post about Clean Architecture later.
Features
- Markdown post editor
- File management
- Light-weight using Razor Pages
- SEO optimized
- Open Graph protocol
- Clean Architecture
- Entity Framework Core, SQL database
- Azure Blob Storage, for file storage
- ..only a blogging engine, nothing else..
What is not included
Because PineBlog is very light-weight it is not a complete website, it needs to be integrated in an existing web application of you need to create a basic web application for it. There are a few things PineBlog depends on, but that it does not provide.
- Authentication and authorization
Note: The admin pages require that authentication/authorization has been setup in your website, the admin area has a
AuthorizeFilter
with the default policy set to all pages in that area folder.
Where can I get it?
You can install the Opw.PineBlog metapackage from the console.
> dotnet add package Opw.PineBlog
The Opw.PineBlog metapackage includes the following packages.
Opw.PineBlog.EntityFrameworkCore package
The PineBlog data provider that uses Entity Framework Core.
Opw.PineBlog.RazorPages package
The PineBlog UI using ASP.NET Core MVC Razor Pages.
Opw.PineBlog.Core package
The PineBlog core package. This package is a dependency forOpw.PineBlog.RazorPages
andOpw.PineBlog.EntityFrameworkCore
.
Getting started
You add the PineBlog services and the RazorPages UI in the Startup.cs of your application.
public void ConfigureServices(IServiceCollection services)
{
...
services.AddPineBlog(Configuration);
services.AddMvc().AddPineBlogRazorPages();
// or services.AddMvcCore().AddPineBlogRazorPages();
...
}
Configuration
A few properties need to be configured before you can run your web application with PineBlog.
{
"ConnectionStrings": {
"DefaultConnection": "Server=inMemory; Database=pineblog-db;"
},
"PineBlogOptions": {
"Title": "PineBlog",
"Description": "A blogging engine based on ASP.NET Core MVC Razor Pages and Entity Framework Core",
"ItemsPerPage": 5,
"CreateAndSeedDatabases": true,
"ConnectionStringName": "DefaultConnection",
"AzureStorageConnectionString": "UseDevelopmentStorage=true",
"AzureStorageBlobContainerName": "pineblog",
"FileBaseUrl": "http://127.0.0.1:10000/devstoreaccount1"
}
}
Blog layout page
For the Blog area you need to override the _Layout.cshtml
for the pages, to do this create a new _Layout.cshtml
page in the Areas/Blog/Shared
folder. This will make the blog pages use that layout page instead of the one included in the Opw.PineBlog.RazorPages
package.
In the new page you can set the layout page of your website. Make sure to add the head
and script
sections.
@{
Layout = "~/Pages/Shared/_Layout.cshtml";
}
@section head {
@RenderSection("head", required: false)
}
@section scripts {
@RenderSection("scripts", required: false)
}
@RenderBody()
Your layout page
PineBlog is dependent on Bootstrap 4.3 and Font Awesome 4.7, so make sure to include them in your layout page and add the necessary files to the wwwroot
of your project (see the sample project for an example).
<html>
<head>
...
<environment include="Development">
<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Open+Sans:400,700|Merriweather:700">
<link rel="stylesheet" href="~/css/bootstrap.css" />
<link rel="stylesheet" href="~/css/font-awesome.min.css">
</environment>
<environment exclude="Development">
<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Open+Sans:400,700|Merriweather:700">
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css"
asp-fallback-href="~/css/bootstrap.min.css"
asp-fallback-test-class="sr-only"
asp-fallback-test-property="position"
asp-fallback-test-value="absolute"
integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T"
crossorigin="anonymous">
<link rel="stylesheet" href="~/css/font-awesome.min.css" asp-append-version="true">
</environment>
...
</head>
<body>
...
<environment include="Development">
<script src="~/js/jquery.js"></script>
<script src="~/js/popper.min.js"></script>
<script src="~/js/bootstrap.js"></script>
</environment>
<environment exclude="Development">
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"
asp-fallback-src="~/js/jquery.min.js"
asp-fallback-test="window.jQuery"
integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8="
crossorigin="anonymous">
</script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js"
integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1"
crossorigin="anonymous">
</script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"
asp-fallback-src="~/js/bootstrap.min.js"
asp-fallback-test="window.jQuery && window.jQuery.fn && window.jQuery.fn.modal"
integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM"
crossorigin="anonymous">
</script>
</environment>
</body>
</html>
Overriding the UI
You can override any other Razor view you like by following the same steps as described above for the layout page. For an example have a look at the sample project where we override the footer (_Footer.cshtml).
Admin layout page
For the Admin area layout page do the same as you did for the Blog area.
...more
For more information, please check PineBlog on GitHub.