在 Persistence 项目中设置 DbContext 导致错误 .NET 7

Question

我有一个包含我的 ApplicationDbContext 类的 Persistence 项目，我希望在这个项目中创建迁移。

Persistence.Context.DbContext

public class PizzaDeliveryDbContext : DbContext
{
    private readonly IConfiguration _config;

    public PizzaDeliveryDbContext(IConfiguration config)
    {
        _config = config;
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseNpgsql(_config.GetConnectionString("pizza"));
    }

    // each dbset maps to a table that will be created in the database
    public DbSet<Customer> Customers { get; set; }

    public DbSet<Order> Orders { get; set; }

    public DbSet<Product> Products { get; set; }

    public DbSet<OrderDetail> OrderDetails { get; set; }

}

在我的启动项目中（与 Persistence 分开）

using Microsoft.EntityFrameworkCore;
using Persistence.Context;

var builder = WebApplication.CreateBuilder(args);
var connectionString = builder.Configuration.GetConnectionString("pizza");

// register dbcontext
builder.Services.AddDbContext<PizzaDeliveryDbContext>(options =>
    options.UseNpgsql(connectionString));

var app = builder.Build();

当我尝试运行

dotnet ef migrations add InitialCreate

（指向持久目录）时-我收到以下错误：

/user Persistence % dotnet ef migrations add InitialCreate
Build started...
Build succeeded.
Unable to create an object of type 'PizzaDeliveryDbContext'. For 

the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

Running dotnet ef migrations add InitialCreate -verbose

    Finding DbContext classes...
    Finding IDesignTimeDbContextFactory implementations...
    Finding application service provider in assembly 'Persistence'...
    Finding Microsoft.Extensions.Hosting service provider...
    No static method 'CreateHostBuilder(string[])' was found on class 'Program'.
    No application service provider was found.
    Finding DbContext classes in the project...
    Found DbContext 'PizzaDeliveryDbContext'.
    Microsoft.EntityFrameworkCore.Design.OperationException: Unable to create an object of type 'PizzaDeliveryDbContext'.
---> System.InvalidOperationException: Unable to resolve service for type 'Microsoft.Extensions.Configuration.IConfiguration' while attempting to activate 'Persistence.Context.PizzaDeliveryDbContext'.
   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__DisplayClass21_4.<FindContextTypes>b__13()
   --- End of inner exception stack trace ---
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass21_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)

Answer 1

您不必从配置中获取连接字符串，因为您已经将它添加到

databasecontext

选项提供程序。除此之外，您没有初始化

DbContext

的新实例

您必须添加

: base(options)

，以创建一个新实例，该实例也将能够获取您在

startup.cs

中指定的连接字符串。

替换

private readonly IConfiguration _config;

public PizzaDeliveryDbContext(IConfiguration config) 
{
   _config = config;
}

protected override void OnConfiguring(DbContextOptionsBuilderoptionsBuilder)
{
   optionsBuilder.UseNpgsql(_config.GetConnectionString("pizza"));
}

与

public PizzaDeliveryDbContext(DbContextOptions<PizzaDeliveryDbContext> options) : base(options)
{
}