[英]Established dependency injection in .NET Core Console Application for EF Core DbContext Service Error
我创建了一个 .net 核心控制台应用程序,并添加了以下依赖注入 package:
Microsoft.Extensions.DependencyInjection
要注入 EF Core DbContext 服务,下面是项目的代码片段:
static void Main(string[] args)
{
// Create service collection and configure our services
var services = ConfigureServices();
// Generate a provider
var serviceProvider = services.BuildServiceProvider();
// Kick off our actual code
serviceProvider.GetService<Startup>().Run();
}
public static IConfiguration LoadConfiguration()
{
var builder = new ConfigurationBuilder()
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
.AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production"}.json", optional: true)
.AddEnvironmentVariables();
return builder.Build();
}
private static IServiceCollection ConfigureServices()
{
IServiceCollection services = new ServiceCollection();
// Set up the objects we need to get to configuration settings
var configuration = LoadConfiguration();
// IMPORTANT! Register our cvonfig file, db connection string, and application entry point(startup)
services
.AddSingleton(configuration)
.AddConnection(configuration)
.AddStartup();
return services;
}
服务池 CLass:
public static class ServicesPool
{
public static IServiceCollection AddStartup(this IServiceCollection services)
{
services.AddTransient<Startup>();
return services;
}
public static IServiceCollection AddConfiggguration(this IServiceCollection services, IConfiguration configuration)
{
services.AddSingleton(configuration);
return services;
}
public static IServiceCollection AddConnection(this IServiceCollection services, IConfiguration configuration)
{
var connection = configuration.GetConnectionString("DEV_CS");
services.AddDbContext<MigrationDbContext>(options =>
options.UseSqlServer(connection, b => b.MigrationsAssembly("migration.presentence")));
return services;
}
}
从 EntityFramwork Core 实现 DbContext 的 MigrationDbContext 服务:
public class MigrationDbContext : DbContext
{
public MigrationDbContext(DbContextOptions dbContextOptions) : base(dbContextOptions)
{
}
public DbSet<RootItemMigrationEntity> RootItems { get; set; }
}
应用程序运行没有任何问题,但是当我尝试使用以下命令创建初始迁移时:
添加迁移“初始”
发生错误并显示以下消息:
无法创建“MigrationDbContext”类型的 object。 有关设计时支持的不同模式,请参阅https://go.microsoft.com/fwlink/?linkid=851728
我一直在调查这个问题,我尝试了多种解决方案,但我还没有解决它。 因此,我将分享错误的堆栈跟踪,希望得到您的帮助!
堆栈跟踪:
PM> Add-Migration 'Initial' -verbos 使用项目'migration.presentence'。 使用启动项目“e-commerce.migration”。 构建开始...构建成功。 C:\Program Files\dotnet\dotnet.exe exec --depsfile C:\dev\backlogheros\e-commerce.migration\e-commerce.migration\bin\Debug\netcoredapp5.0\e-commerce.migration。 json --additionalprobingpath C:\Users\yousi.nuget\packages --runtimeconfig C:\dev\backlogheros\e-commerce.migration\e-commerce.migration\bin\Debug\netcoreapp5.0\e-commerce.migration. runtimeconfig.json C:\Users\yousi.nuget\packages\microsoft.entityframeworkcore.tools\5.0.1\tools\netcoreapp2.0\any\ef.dll migrations add Initial --json --verbose --no-color - -prefix-output --assembly C:\dev\backlogheros\e-commerce.migration\e-commerce.migration\bin\Debug\netcoreapp5.0\migration.presentence.dll --startup-assembly Z0D6 1F8370CAD1D412F80B84D143E1257Z:\dev\backlogheros\e-commerce.migration\e-commerce.migration\bin\Debug\netcoreapp5.0\e-commerce.migration.dll --project-dir C:\dev\backlogheros\e-commerce.迁移\migration.presentence
--language C# --working-dir C:\dev\backlogheros\e-commerce.migration --root-namespace migration.presentence 使用程序集“migration.presentence”。 使用启动程序集“e-commerce.migration”。 使用应用程序库“C:\dev\backlogheros\e-commerce.migration\e-commerce.migration\bin\Debug\netcoreapp5.0”。 使用工作目录'C:\dev\backlogheros\e-commerce.migration\e-commerce.migration'。 使用根命名空间“migration.presentence”。 使用项目目录'C:\dev\backlogheros\e-commerce.migration\migration.presentence'。 剩余的 arguments:。 查找 DbContext 类...查找 IDesignTimeDbContextFactory 实现...查找程序集“e-commerce.migration”中的应用程序服务提供程序...查找 Microsoft.Extensions.Hosting 服务提供程序...无 static 方法“CreateHostBuilder(string[])”在 class '程序'上找到。 未找到应用程序服务提供者。 在项目中查找 DbContext 类...找到 DbContext 'MigrationDbContext'。 Microsoft.EntityFrameworkCore.Design.OperationException:无法创建“MigrationDbContext”类型的 object。 有关设计时支持的不同模式,请参阅https://go.microsoft.com/fwlink/?linkid=851728 ---> System.InvalidOperationException: Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContextOptions' while trying to激活'migration.presentence.MigrationDbContext'。
at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.ConstructorMatcher.CreateInstance(IServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.CreateInstance(IServiceProvider provider, Type instanceType, Object[] parameters)
at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetServiceOrCreateInstance(IServiceProvider provider, Type type)
at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass13_4.<FindContextTypes>b__13()
--- End of inner exception stack trace ---
at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass13_4.<FindContextTypes>b__13()
at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func`1 factory)
at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)
at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType, String namespace)
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType, String namespace)
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration.<>c__DisplayClass0_0.<.ctor>b__0()
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
迁移工具必须实例化您的 DbContext 才能创建迁移。 它有 3 种方法可以做到这一点:
如果您希望迁移工具使用应用程序配置并从服务提供商处解析 DbContext,则有多个要求,如https://go.microsoft.com/fwlink/?linkid=851728页所述。
首先,您需要有一个在您的DbContextOptions
上采用 DbContextOptions 的构造函数。 那部分没问题,只有在程序集中有多个 DbContext 时才需要指定DbContextOptions<TContext>
。
Second, you must use a host builder (either ASP.NET, HTTP or Generic) and the tool will look for a public static CreateHostBuilder(string[] args)
method in class Program
to access it. 这对您的基础架构类有很多副作用,因为IHostBuilder
将为您完成大部分ServiceCollection
和ConfigurationBuilder
的工作。
此外,您的 DbContext 需要注册为 singleton,这可能是个问题。
程序.cs
internal class Program
{
public static void LoadConfiguration(HostBuilderContext host, IConfigurationBuilder builder)
{
builder
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
.AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production"}.json", optional: true)
.AddEnvironmentVariables();
}
private static void ConfigureServices(HostBuilderContext host, IServiceCollection services)
{
services
.AddDbContext<MigrationDbContext>(options =>
{
options.UseSqlServer(
host.Configuration.GetConnectionString("DEV_CS"), builder =>
builder.MigrationsAssembly("migration.presentence"));
}, ServiceLifetime.Singleton)
.AddHostedService<Startup>();
}
private static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureAppConfiguration(LoadConfiguration)
.ConfigureServices(ConfigureServices);
private static async Task Main(string[] args)
{
CreateHostBuilder(args).Build().Run();
}
}
为了让您的主机构建器运行您的自定义代码,您还需要将Startup
class 转换为IHostedService
,例如BackgroundService
。
启动.cs
internal class Startup : BackgroundService
{
private readonly MigrationDbContext context;
public Startup(MigrationDbContext context)
{
this.context = context ?? throw new ArgumentNullException(nameof(context));
}
protected override Task ExecuteAsync(CancellationToken stoppingToken)
{
throw new NotImplementedException();
}
}
另一种选择是在 DbContext 上使用默认构造。 但是,在这种情况下,您不能同时拥有默认构造函数和DbContextOptions
构造函数。 伤心。
在您的情况下,最简单的解决方案可能是实现IDesignTimeDbContextFactory<TContext>
。 如果找不到IHostBuilder
并且 DbContext 使用DbContextOptions
构造函数,则工具将使用此 class。 实现非常简单:
internal class MigrationDbContextFactory : IDesignTimeDbContextFactory<MigrationDbContext>
{
public MigrationDbContext CreateDbContext(string[] args)
{
var optionsBuilder = new DbContextOptionsBuilder<MigrationDbContext>();
optionsBuilder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=Test",
b => b.MigrationsAssembly("migration.presentence"));
return new MigrationDbContext(optionsBuilder.Options);
}
}
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