ConfigurationRepository

A class library for ASP .NET Core applications for using databases as configuration repositories.

Installation:

• from NuGet;
• from package manager console:

Install-Package ConfigurationRepository

• from command line:

dotnet add package ConfigurationRepository

Dapper configuration repository

EntityFramework configuration repository

SqlClient configuration repository

Ms Sql Server + Dapper:

Let's assume that we have a database that stores a configuration table as key-value pairs:

create table Configuration
(
    [Key]   varchar(800)  not null primary key clustered,
    [Value] nvarchar(max)     null
);

insert Configuration ([Key], [Value])
values ('Logging:LogLevel:Default', N'Information'),
       ('Logging:LogLevel:Microsoft.AspNetCore', N'Warning');

This script defines a table with non-nullable Key column used as primary key and nullable Value column. The hierarchy of keys is linearized by colon [:] separators. The names of the table, columns and keys/indexes on them can be any.

So then in our application Program.cs file we may add a configuration provider like this:

var builder = WebApplication.CreateBuilder(args);

var connectionString = builder.Configuration.GetConnectionString("Dapper");

builder.Configuration.AddDapperRepository(
    repository => repository
        .UseDbConnectionFactory(() => new SqlConnection(connectionString))
        .WithSelectConfigurationQuery("select \"Key\", \"Value\" from Configuration"));

var app = builder.Build();

app.Run();

Here we:

• extract connection string named "Dapper" from existing configuration providers (i.e. appsettings.json);
• add database repository using Dapper with AddDapperRepository() extension method;
• define database connection factory that will create database connection for our provider using UseDbConnectionFactory() extension method and our connection string;
• define the select configuration query with WithSelectConfigurationQuery() extension method.

If our database source can change at any time in any way we may also add configuration reloader that with periodically reload our configuration from database:

var builder = WebApplication.CreateBuilder(args);

var connectionString = builder.Configuration.GetConnectionString("Dapper");

builder.Configuration.AddDapperRepository(
    repository => repository
        .UseDbConnectionFactory(() => new SqlConnection(connectionString))
        .WithSelectConfigurationQuery("select \"Key\", \"Value\" from Configuration"),
    source => source.WithPeriodicalReload());

builder.Services.AddConfigurationReloader();

var app = builder.Build();

app.Run();

Here we additionaly:

• define that our configuration provider source will use PeriodicalReload background service;
• register PeriodicalReload background service in our service collection.

We can define reload period as a time span passed as a parameter to WithPeriodicalReload() exstension method.

What if our config in database is too heavy to reload it frequently and we want to minimize our network traffic? Let`s just version our configurations adding a rowversion column to the configuration table:

create table Configuration
(
    [Key]     varchar(800)  not null primary key clustered,
    [Value]   nvarchar(max)     null,
    [Version] rowversion    not null unique
);

insert Configuration ([Key], [Value])
values ('Logging:LogLevel:Default', N'Information'),
       ('Logging:LogLevel:Microsoft.AspNetCore', N'Warning');

Here we additionaly:

• add a Version column of type rowversion to Configuration table;
• mark Version column with uniqe constraint to get an indexed column.

Then we make our configuration versioned by adding SelectCurrentVersionQuery to our repository:

var builder = WebApplication.CreateBuilder(args);

var connectionString = builder.Configuration.GetConnectionString("Dapper");

builder.Configuration.AddDapperRepository(
    repository => repository
        .UseDbConnectionFactory(() => new SqlConnection(connectionString))
        .WithSelectConfigurationQuery("select \"Key\", \"Value\" from Configuration")
        .WithSelectCurrentVersionQuery("select max(\"Version\") from Configuration"),
    source => source.WithPeriodicalReload());

builder.Services.AddConfigurationReloader();

var app = builder.Build();

app.Run();

Here we additionaly add WithSelectCurrentVersionQuery() extension method passing query that selects current configuration version.

ParametrizedConfiguration

ParametrizedConfiguration library presents a configuration provider that uses it`s own configuration data via other providers to parametrize parameter placeholders with values, accessed by parameter keys. By default placeholders defined between two % symbols like %param name%, where param name should be the key of the same configuration, the value of which will be substituted into %param name%. for example: This configuration:

{
  { "param1", "1+%param2%" },
  { "param2", "2+%param3%" },
  { "param3", "3" }
};

will be parametrized into this:

{
  { "param1", "1+2+3" },
  { "param2", "2+3" },
  { "param3", "3" }
};

This can be used to hide sensitive data from publicly stored configurations or to reuse same configuration values in several places. The code below demonstrates this:

using ParametrizedConfiguration;
using Microsoft.Extensions.Configuration;

// Assume secrets are set via environment variables somewere outside this code,
// we set them here just for clarity:
Environment.SetEnvironmentVariable("DatabaseName", "MyDatabase");
Environment.SetEnvironmentVariable("UserName", "Bob");
Environment.SetEnvironmentVariable("Password", "strongPassword");

// Define configuration that will be parametrized with it`s own values:
var configuration = new ConfigurationBuilder()
    .AddEnvironmentVariables()
    .WithParametrization()
    .Build();

// Let`s define our configuration key with parameters. It also won't be here
// in our production code, but will be loaded from configuration providers
// such as json-files or any other defined in ConfigurationBuilder.
configuration["ConnectionStrings:Mssql"] =
    "Server=mssql-server;Database=%DatabaseName%;User Id=%UserName%;Password=%Password%;TrustServerCertificate=True";

// Ok, now let`s get the connection string from configuration:
Console.WriteLine(configuration.GetConnectionString("mssql"));

// Output will be parametrized with values from same configuration:
// Server=mssql-server;Database=MyDatabase;User Id=Bob;Password=strongPassword;TrustServerCertificate=True