| title | description | author | ms.author | ms.date | ms.topic |
|---|---|---|---|---|---|
Implement a custom configuration provider |
Learn how to implement a custom configuration provider in .NET apps. Explore a database configuration provider that uses Entity Framework Core. |
IEvangelist |
dapine |
02/20/2024 |
how-to |
There are many configuration providers available for common configuration sources such as JSON, XML, and INI files. You may need to implement a custom configuration provider when one of the available providers doesn't suit your application needs. In this article, you'll learn how to implement a custom configuration provider that relies on a database as its configuration source.
The sample app demonstrates how to create a basic configuration provider that reads configuration key-value pairs from a database using Entity Framework (EF) Core.
The provider has the following characteristics:
- The EF in-memory database is used for demonstration purposes.
- To use a database that requires a connection string, get a connection string from an interim configuration.
- The provider reads a database table into configuration at startup. The provider doesn't query the database on a per-key basis.
- Reload-on-change isn't implemented, so updating the database after the app has started will not affect the app's configuration.
Define a Settings record type entity for storing configuration values in the database. For example, you could add a Settings.cs file in your Models folder:
:::code language="csharp" source="snippets/configuration/custom-provider/Models/Settings.cs":::
For information on record types, see Record types in C#.
Add an EntityConfigurationContext to store and access the configured values.
Providers/EntityConfigurationContext.cs:
:::code language="csharp" source="snippets/configuration/custom-provider/Providers/EntityConfigurationContext.cs":::
By overriding xref:Microsoft.EntityFrameworkCore.DbContext.OnConfiguring(Microsoft.EntityFrameworkCore.DbContextOptionsBuilder) you can use the appropriate database connection. For example, if a connection string was provided you could connect to SQL Server, otherwise you could rely on an in-memory database.
Create a class that implements xref:Microsoft.Extensions.Configuration.IConfigurationSource.
Providers/EntityConfigurationSource.cs:
:::code language="csharp" source="snippets/configuration/custom-provider/Providers/EntityConfigurationSource.cs":::
Create the custom configuration provider by inheriting from xref:Microsoft.Extensions.Configuration.ConfigurationProvider. The configuration provider initializes the database when it's empty. Since configuration keys are case-insensitive, the dictionary used to initialize the database is created with the case-insensitive comparer (StringComparer.OrdinalIgnoreCase).
Providers/EntityConfigurationProvider.cs:
:::code language="csharp" source="snippets/configuration/custom-provider/Providers/EntityConfigurationProvider.cs":::
An AddEntityConfiguration extension method permits adding the configuration source to the underlying ConfigurationManager instance.
Extensions/ConfigurationManagerExtensions.cs:
:::code language="csharp" source="snippets/configuration/custom-provider/Extensions/ConfigurationManagerExtensions.cs":::
Since the xref:Microsoft.Extensions.Configuration.ConfigurationManager is both an implementation of xref:Microsoft.Extensions.Configuration.IConfigurationBuilder and xref:Microsoft.Extensions.Configuration.IConfigurationRoot, the extension method can access the connection strings configuration and add the EntityConfigurationSource.
The following code shows how to use the custom EntityConfigurationProvider in Program.cs:
:::code language="csharp" source="snippets/configuration/custom-provider/Program.cs" highlight="9":::
To consume the custom configuration provider, you can use the options pattern. With the sample app in place, define an options object to represent the widget settings.
:::code language="csharp" source="snippets/configuration/custom-provider/WidgetOptions.cs":::
A call to xref:Microsoft.Extensions.DependencyInjection.OptionsConfigurationServiceCollectionExtensions.Configure%2A registers a configuration instance, which TOptions binds against.
:::code language="csharp" source="snippets/configuration/custom-provider/Program.cs" highlight="14,16-19":::
The preceding code configures the WidgetOptions object from the "WidgetOptions" section of the configuration. This enables the options pattern, exposing a dependency injection-ready IOptions<WidgetOptions> representation of the EF settings. The options are ultimately provided from the custom configuration provider.