c# - 如何将默认值从 appsettings 设置为 API 模型上的属性

Question

如何在 .NET Core 3 框架实例化的模型上为属性设置默认值，从我的 appsettings.json 文件中读取它？

我创建了一个 repo(一个全新的 .NET Core 3 项目)，我试图在其中说明问题:https://github.com/NelsonPRSousa/dependency-injection-default-constructor

API 操作:

[HttpGet]
public IEnumerable<WeatherForecast> Get([FromQuery] FilteringRequestModel request)
{

    var defaultType = request.Type;

    var rng = new Random();
    return Enumerable.Range(1, 5).Select(index => new WeatherForecast
    {
        Date = DateTime.Now.AddDays(index),
        TemperatureC = rng.Next(-20, 55),
        Summary = Summaries[rng.Next(Summaries.Length)]
    })
    .ToArray();
}

型号:

public class FilteringRequestModel
{
    /* Please note that we must have a parameterless constructor, since it's the framework responsability to instatiate this object
     * when invoking this action: IEnumerable<WeatherForecast> Get([FromQuery] FilteringRequestModel request)
     */

    public FilteringRequestModel()
    {
        //Type = System.Configuration.ConfigurationManager.AppSettings["DefaultTypeTopRated"];
    }

    public string Type { get; set; } = "top_rated"; // TODO: Read from appsettings
}

Answer 1

您可以将 IOptions 与依赖注入(inject)一起使用

更新FilteringRequestModel类

public class FilteringRequestModel
{
    public FilteringRequestModel()
    {
    }

    public void Initialize(IOptions<FilteringRequestSettings> settings)
    {
        if (string.IsNullOrEmpty(this.Type))
        {
            this.Type = settings.Value.Type;
        }
    }

    public string Type { get; set; }
}

添加 FilteringRequestSettings类

public class FilteringRequestSettings
{
    public string Type { get; set; }
}

更新appsettings.Development.json像这样

{
  "Logging": {
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Information"
    }
  },
  "FilteringRequest": {
    "Type":  "foo"
  }
}

更新ConfigureServices Startup 中的方法像这样上课

public void ConfigureServices(IServiceCollection services)
{
    services.Configure<FilteringRequestSettings>(this.Configuration.GetSection("FilteringRequest"));

    services.AddControllers();
}

最后，更新WeatherForecastController像这样上课

[HttpGet]
public IEnumerable<WeatherForecast> Get([FromQuery] FilteringRequestModel request)
{
    request.Initialize(_settings);

    var defaultType = request.Type;

    var rng = new Random();
    return Enumerable.Range(1, 5).Select(index => new WeatherForecast
    {
        Date = DateTime.Now.AddDays(index),
        TemperatureC = rng.Next(-20, 55),
        Summary = Summaries[rng.Next(Summaries.Length)]
    })
    .ToArray();
}

解释

• 您将从 appsettings 加载参数到 IOptions<FilteringRequestSettings>
• IOptions<FilteringRequestSettings>会被注入(inject) WeatherForecastController
• 然后您将调用 Initialize方法你 request参数与 IOptions<FilteringRequestSettings>
• Initialize方法验证是否 Type尚未设置属性(来自查询/请求)。如果不是，它将使用来自 appsettings 的值(通过 IOptions<FilteringRequestSettings>