ASP.NET Core的配置（4）：多样性的配置来源[下篇]

2023-01-05 17:55:37

我们在上篇和中篇对配置模型中默认提供的各种ConfigurationProvider进行了深入详尽的介绍，如果它们依然不能满足项目中的配置需求，我们可以还可以通过自定义ConfigurationProvider来支持我们希望的配置来源。就配置数据的持久化方式来说，将配置存储在数据库中应该是一种非常常见的方式，接下来我们就是创建一个针对数据库的ConfigurationProvider，它采用最新的Entity Framework 7来完成数据库的存取操作。

目录
MemoryConfigurationProvider
EnvironmentVariablesConfigurationProvider
CommandLineConfigurationProvider
JsonConfigurationProvider
XmlConfiguationProvider
IniConfigurationProvider
自定义ConfigurationProvider

我们将这个自定义ConfigurationProvider命名为DbConfigurationProvider。在正式对它的实现展开介绍之前，我们先来看看它在项目中的应用。我们创建一个ASP.NET Core控制台程序来演示对这个DbConfigurationProvider应用，由于我们需要使用到Entity Framework 7，并且采用SQL Server数据库，所以我们需要在project.json文件中按照如下的方式添加对“EntityFramework.MicrosoftSqlServer”这个NuGet包的依赖。

   1: {

   2:   ...

   3:   "dependencies": {

   4:     "Microsoft.Extensions.Configuration": "1.0.0-rc1-final",

   5:     "EntityFramework.MicrosoftSqlServer": "7.0.0-rc1-final"

   6:   },

   7: }

我们按照如下的方式读取相关配置并将绑定为一个Profile对象。我们调用自定义的扩展方法AddDatabase创建一个DbConfigurationProvider对象并将其注册到创建的ConfigurationBuilder对象上。我们在调用扩展方法AddDatabase的时候指定了连接的目标数据库，同时设置了一些初始的配置项（如果确保配置项存在于目标数据库中，这个参数是不需要指定的），它们提供了组成一个完整的Profile对象的基础数据。

   1: string connectionString = "...";

   2: Profile profile = new ConfigurationBuilder().AddDatabase(optionsBuilder => optionsBuilder.UseSqlServer(connectionString),

   3:         new Dictionary<string, string>

   4:         {

   5:             ["Profile:Gender"]                    = "Male",

   6:             ["Profile:Age"]                       = "18",

   7:             ["Profile:ContactInfo:Email"]         = "foobar@outlook.com",

   8:             ["Profile:ContactInfo:PhoneNo"]       = "123456789"

   9:         })

  10:     .Build().Get<Profile>("Profile");

如上面的代码片断所示，针对自定义的DbConfigurationProvider的应用仅仅体现在我们为ConfigurationBuilder定义的扩展方法AddDatabase上，所以使用起来是非常方便的，那么这个扩展方法背后有着怎样的逻辑实现呢？DbConfigurationProvider采用Entity Framework 7以Code First的方式进行数据操作，如下所示的ApplicationSetting是表示基本配置项的POCO类型，我们将配置项的Key以小写的方式存储。另一个ApplicationSettingsContext是对应的DbContext类型。

   1: [Table("ApplicationSettings")]

   2: public class ApplicationSetting

   3: {

   4:     private string key;

5:

   6:     [Key]

   7:     public string Key

   8:     {

   9:         get { return key; }

  10:         set { key = value.ToLowerInvariant(); }

  11:     }

12:

  13:     [Required]

  14:     [MaxLength(512)]

  15:     public string Value { get; set; }

16:

  17:     public ApplicationSetting()

  18:     {}

19:

  20:     public ApplicationSetting(string key, string value)

  21:     {

  22:         this.Key     = key;

  23:         this.Value     = value;

  24:     }

  25: }

26:

  27: public class ApplicationSettingsContext : DbContext

  28: {

  29:     public ApplicationSettingsContext(DbContextOptions options) : base(options)

  30:     {}

31:

  32:     public DbSet<ApplicationSetting> Settings { get; set; }

  33: }

如下所示的是DbConfigurationProvider和扩展方法AddDatabase的定义。DbConfigurationProvider它的构造函数具有两个参数，一个参数类型为Action<DbContextOptionsBuilder>，用来对创建DbContext采用的DbContextOptions进行设置，另一个可选的参数用来指定一些需要自动初始化的配置项。在重写的Load方法中，我们利用创建的DbContexts从数据库中读取所有的配置项并作为自身的配置字典。

   1: public class DbConfigurationProvider: ConfigurationProvider

   2: {

   3:     public Func<DbContextOptions> DbContextOptionsAccessor { get; private set; }

4:

   5:     public DbConfigurationProvider(Action<DbContextOptionsBuilder> setup, IEnumerable<KeyValuePair<string, string>> settings = null)

   6:     {

   7:         DbContextOptionsBuilder<ApplicationSettingsContext> optionsBuilder = new DbContextOptionsBuilder<ApplicationSettingsContext>();

   8:         setup(optionsBuilder);

   9:         this.DbContextOptionsAccessor = () => optionsBuilder.Options;

10:

  11:         if (settings!=null && settings.Any())

  12:         {

  13:             using (ApplicationSettingsContext dbContext = new ApplicationSettingsContext(this.DbContextOptionsAccessor()))

  14:             {

  15:                 dbContext.Database.EnsureCreated();

  16:                 foreach (var item in settings)

  17:                 {

  18:                     ApplicationSetting setting = dbContext.Settings.FirstOrDefault(it => it.Key == item.Key.ToLowerInvariant());

  19:                     if (null == setting)

  20:                     {

  21:                         dbContext.Settings.Add(new ApplicationSetting(item.Key, item.Value));

  22:                     }

  23:                     else

  24:                     {

  25:                         setting.Value = item.Value;

  26:                     }

  27:                 }

  28:                 dbContext.SaveChanges();

  29:             }

  30:         }

  31:     }

32:

  33:     public override void Load()

  34:     {

  35:         using (ApplicationSettingsContext dbContext = new ApplicationSettingsContext(this.DbContextOptionsAccessor()))

  36:         {

  37:             var dictionary = dbContext.Settings.ToDictionary(it => it.Key, it => it.Value);

  38:             this.Data = new Dictionary<string, string>(dictionary, StringComparer.OrdinalIgnoreCase);

  39:         }

  40:     }

  41: }

42:

  43: public static class DbConfigurationProviderExtensions

  44: {

  45:     public static IConfigurationBuilder AddDatabase(this IConfigurationBuilder builder, Action<DbContextOptionsBuilder> setup,

  46:         IEnumerable<KeyValuePair<string, string>> settings = null)

  47:     {

  48:         builder.Add(new DbConfigurationProvider(setup, settings));

  49:         return builder;

  50:     }

  51: }

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