如何使用 Action 调用泛型方法<t>在 C# 中使用反射的参数</t>

Question

I want this code to be called generic.

services.AddDbContext<ProductsDbContext>(options =>
{
    options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"),
        sqlServerOptions =>
        {
            sqlServerOptions.MigrationsAssembly("Modules.Products");
        });
});

It's from entityframeworkcore. See the documentation here .

I created a class for getting the builder:

public static class DbContextExtensions
{
    public static Action<DbContextOptionsBuilder> GetDbContextOptionsBuilder(string connectionString, AssemblyName moduleName)
    {
        return options =>
        {
            options.UseSqlServer(connectionString,
                sqlServerOptions =>
                {
                    sqlServerOptions.MigrationsAssembly(moduleName.Name);
                });
        };
    }
}

And I created the following for invoke the method:

var moduleAssembly = Assembly.GetAssembly(manifest);
var moduleName = moduleAssembly.GetName();

// Get dbcontext like ProductsDbContext
var dbContext = moduleAssembly.GetTypes().Where(p => typeof(DbContext).IsAssignableFrom(p)).First();

// Get the correct extensionmethod with Action<DbContextOptionsBuilder>
MethodInfo addDbContextMethod = typeof(EntityFrameworkServiceCollectionExtensions)
    .GetMethod(nameof(EntityFrameworkServiceCollectionExtensions.AddDbContext),
        1,
        new Type[] { typeof(ServiceCollection), typeof(Action<DbContextOptionsBuilder>), typeof(ServiceLifetime), typeof(ServiceLifetime) });
MethodInfo generic = addDbContextMethod.MakeGenericMethod(dbContext);


// But how to pass the Action<DbContextOptionsBuilder> method?
// I tried the following but i'm lost...
var delegateType = typeof(Action<>).MakeGenericType(typeof(DbContextOptionsBuilder));
var methodInfo = typeof(DbContextExtensions).GetMethod(nameof(DbContextExtensions.GetDbContextOptionsBuilder));
var del = Delegate.CreateDelegate(delegateType, null, methodInfo);

// invoke subscribe method
generic.Invoke(services, new[] { del });

Any ideas? Thanks

Answer 1

From your code I see that DbContextExtensions is your local class which you don't need to call using Reflection, so you can call the GetDbContextOptionsBuilder method directly providing the correct parameters and get the action. Then you can call your generic method with the generated actions.

        var moduleAssembly = Assembly.GetAssembly(manifest);            
        var moduleName = moduleAssembly.GetName();
        var dbContext = moduleAssembly.GetTypes().Where(p => typeof(DbContext).IsAssignableFrom(p)).First();


        MethodInfo addDbContextMethod = typeof(EntityFrameworkServiceCollectionExtensions)
            .GetMethod(nameof(EntityFrameworkServiceCollectionExtensions.AddDbContext),
                1,
                new Type[] { typeof(IServiceCollection), typeof(Action<DbContextOptionsBuilder>), typeof(ServiceLifetime), typeof(ServiceLifetime) });

        MethodInfo generic = addDbContextMethod.MakeGenericMethod(dbContext);

        var action = DbContextExtensions.GetDbContextOptionsBuilder("connectionString", moduleName);

        generic.Invoke(null, new object[] { services, action, ServiceLifetime.Scoped, ServiceLifetime.Scoped });

If you want to get the action from the external assembly, you can use the same approach by dynamically getting the GetDbContextOptionsBuilder method info and calling it with parameters and as the result you get the action which you can use in calling your generic method.