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[英]Use IWebHostEnvironment in Program.cs web host builder in ASP.NET Core 3.1
[英]How to access IWebHostEnvironment from Program.cs in ASP.NET Core
我有 ASP.NET 核心 Razor 页面应用程序,我想在我的Program.cs
中访问IWebHostEnvironment
。 我在应用程序开始时为 DB 播种,我需要将IWebHostEnvironment
传递给我的初始化程序。 这是我的代码:
程序.cs
public class Program
{
public static void Main(string[] args)
{
var host = CreateHostBuilder(args).Build();
using (var scope = host.Services.CreateScope())
{
var services = scope.ServiceProvider;
try
{
SeedData.Initialize(services);
}
catch (Exception ex)
{
var logger = services.GetRequiredService<ILogger<Program>>();
logger.LogError(ex, "An error occurred seeding the DB.");
}
}
host.Run();
}
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseStartup<Startup>();
});
}
种子数据.cs
public static class SeedData
{
private static IWebHostEnvironment _hostEnvironment;
public static bool IsInitialized { get; private set; }
public static void Init(IWebHostEnvironment hostEnvironment)
{
if (!IsInitialized)
{
_hostEnvironment = hostEnvironment;
IsInitialized = true;
}
}
public static void Initialize(IServiceProvider serviceProvider)
{
//List<string> imageList = GetMovieImages(_hostEnvironment);
int d = 0;
using var context = new RazorPagesMovieContext(
serviceProvider.GetRequiredService<
DbContextOptions<RazorPagesMovieContext>>());
if (context.Movie.Any())
{
return; // DB has been seeded
}
var faker = new Faker("en");
var movieNames = GetMovieNames();
var genreNames = GetGenresNames();
foreach(string genreTitle in genreNames)
{
context.Genre.Add(new Genre { GenreTitle = genreTitle });
}
context.SaveChanges();
foreach(string movieTitle in movieNames)
{
context.Movie.Add(
new Movie
{
Title = movieTitle,
ReleaseDate = GetRandomDate(),
Price = GetRandomPrice(5.5, 30.5),
Rating = GetRandomRating(),
Description = faker.Lorem.Sentence(20, 100),
GenreId = GetRandomGenreId()
}
);
}
context.SaveChanges();
}
因为我在wwwroot
中有图像,我需要在初始化期间从那里获取图像的名称。 我尝试在配置方法中从Startup.cs传递IWebHostEnvironment
:
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
int d = 0;
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Error");
// The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
app.UseHsts();
}
SeedData.Init(env); // Initialize IWebHostEnvironment
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapRazorPages();
});
}
但似乎Startup.Configure
方法在Program.Main
方法之后执行。 然后我决定在Startup.ConfigureServices
方法中进行,但事实证明该方法最多只能占用 1 个参数。 有什么办法可以做到这一点? 但是,我不确定我尝试播种数据的方式是最好的方式,我只是认为这种方式最适合我的情况,所以我非常感谢任何其他建议的方法。
我发现的类似问题:
原始问题演示了如何尝试将 DI 与 static 类一起使用会导致比它解决的问题更多的问题。
播种器可以是一个作用域注册的 class 并在构建后从主机解析。 主机环境和任何其他依赖项可以通过构造函数注入显式注入
例如
public class SeedData {
private readonly IWebHostEnvironment hostEnvironment;
private readonly RazorPagesMovieContext context;
private readonly ILogger logger;
public SeedData(IWebHostEnvironment hostEnvironment, RazorPagesMovieContext context, ILogger<SeedData> logger) {
this.hostEnvironment = hostEnvironment;
this.context = context;
this.logger = logger;
}
public void Run() {
try {
List<string> imageList = GetMovieImages(hostEnvironment); //<<-- USE DEPENDENCY
int d = 0;
if (context.Movie.Any()) {
return; // DB has been seeded
}
var faker = new Faker("en");
var movieNames = GetMovieNames();
var genreNames = GetGenresNames();
foreach(string genreTitle in genreNames) {
context.Genre.Add(new Genre { GenreTitle = genreTitle });
}
context.SaveChanges();
foreach(string movieTitle in movieNames) {
context.Movie.Add(
new Movie {
Title = movieTitle,
ReleaseDate = GetRandomDate(),
Price = GetRandomPrice(5.5, 30.5),
Rating = GetRandomRating(),
Description = faker.Lorem.Sentence(20, 100),
GenreId = GetRandomGenreId()
}
);
}
context.SaveChanges();
} catch (Exception ex) {
logger.LogError(ex, "An error occurred seeding the DB.");
}
}
// ... other code
}
请注意不再需要服务定位器反模式。 所有必要的依赖项都根据需要显式注入到 class 中。
然后可以简化Program
public class Program {
public static void Main(string[] args) {
var host = CreateHostBuilder(args).Build();
using (var scope = host.Services.CreateScope()) {
SeedData seeder = scope.ServiceProvider.GetRequiredService<SeedData>();
seeder.Run();
}
host.Run();
}
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureServices(services => {
services.AddScoped<SeedData>(); //<-- NOTE
})
.ConfigureWebHostDefaults(webBuilder => {
webBuilder.UseStartup<Startup>();
});
}
播种机在主机上注册并在运行主机之前根据需要进行解析。 现在不需要访问除了播种机之外的任何东西。 IWebHostEnvironment
和所有其他依赖项将由 DI 容器解析并在需要的地方注入。
我的问题的解决方案是简单地从ServiceProvider.GetRequiredService<T>
请求IWebHostEnvironment
:
主要的
var host = CreateHostBuilder(args).Build();
using (var scope = host.Services.CreateScope())
{
var services = scope.ServiceProvider;
var hostEnvironment = services.GetRequiredService<IWebHostEnvironment>();
try
{
SeedData.Initialize(services, hostEnvironment);
}
catch (Exception ex)
{
var logger = services.GetRequiredService<ILogger<Program>>();
logger.LogError(ex, "An error occurred seeding the DB.");
}
}
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