asp.net core 将配置文件配置迁移到数据库（一）

Intro

asp.net core 配置默认是项目根目录下的 appsettings.json 文件，还有环境变量以及 command line arguments，有一些链接字符串等信息可能放在数据库里更好一些，也方便修改与维护，有的配置可能多个应用共享一些配置，这样维护在数据库里可能就只需要配置一次。有人可能说那你为什么不直接搞个配置中心呢，开始是想直接接入一个配置中心，后来觉得项目不大可以不必引入配置中心，直接自己造个轮子从数据库读取配置就可以了，于是就想自己实现一套基于数据库的 ConfigurationProvider

探索 Configuration

Configuration 源码在 https://github.com/aspnet/Extensions/tree/master/src/Configuration

微软也提供了一些自己实现的 ConfigurationProvider

自定义基于 EF 的 ConfigurationProvider

需要实现两个接口

1. 实现

   IConfigurationProvider

   接口

using System.Linq;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;

namespace WeihanLi.Configuration.EntityFramework
{
internal class EntityFrameworkConfigurationProvider : ConfigurationProvider
{
private readonly DbContextOptions<ConfigurationsDbContext> _dbContextOptions;

public EntityFrameworkConfigurationProvider(DbContextOptions<ConfigurationsDbContext> dbContextOptions)
{
_dbContextOptions = dbContextOptions;
}

public override void Load()
{
using (var dbContext = new ConfigurationsDbContext(_dbContextOptions))
{
var configurations = dbContext.Configurations.AsNoTracking()
.ToArray();
if (configurations.Length == 0)
return;

foreach (var configuration in configurations)
{
Data[configuration.Key] = configuration.Value;
}
}
}
}
}

1. 实现

   IConfigurationSource

   接口

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;

namespace WeihanLi.Configuration.EntityFramework
{
internal class EntityFrameworkConfigurationSource : IConfigurationSource
{
private readonly Action<DbContextOptionsBuilder<ConfigurationsDbContext>> _action;

public EntityFrameworkConfigurationSource(Action<DbContextOptionsBuilder<ConfigurationsDbContext>> action)
{
_action = action;
}

private readonly DbContextOptionsBuilder<ConfigurationsDbContext> DbContextOptionsBuilder = new DbContextOptionsBuilder<ConfigurationsDbContext>();

public IConfigurationProvider Build(IConfigurationBuilder builder)
{
_action.Invoke(DbContextOptionsBuilder);
return new EntityFrameworkConfigurationProvider(DbContextOptionsBuilder.Options);
}
}
}

扩展方法：

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;

namespace WeihanLi.Configuration.EntityFramework
{
public static class RedisConfigurationExtension
{
/// <summary>
/// Adds an <see cref="IConfigurationProvider"/> that reads configuration values from EntityFramework.
/// </summary>
/// <param name="builder">The <see cref="IConfigurationBuilder"/> to add to.</param>
/// <param name="action">Configures the configurationsDbContext source.</param>
/// <returns>The <see cref="IConfigurationBuilder"/>.</returns>
public static IConfigurationBuilder AddEntityFramework(this IConfigurationBuilder builder, Action<DbContextOptionsBuilder<ConfigurationsDbContext>> action)
=> builder.Add(new EntityFrameworkConfigurationSource(action));
}
}

更多源码参考：https://github.com/WeihanLi/AspNetCorePlayground/tree/master/WeihanLi.Configuration.EntityFramework

使用

修改 Program 文件 WebHost 的构建，参考https://github.com/WeihanLi/AspNetCorePlayground/blob/master/TestWebApplication/Program.cs：

WebHost.CreateDefaultBuilder(args)
.ConfigureAppConfiguration(configBuilder =>
{
var configuration = configBuilder.Build();
configBuilder.AddEntityFramework(config => config.UseSqlServer(configuration.GetConnectionString("Configurations"));
})
.UseStartup<Startup>();

源码

你可以修改源码来进一步定制符合你需要的基于数据库的 ConfigurationProvider