Question

我在DbContext中保存实体时会动态注入家政服务。

protected override DbEntityValidationResult ValidateEntity(DbEntityEntry entityEntry, IDictionary<object, object> items)
{
    var t = entityEntry.Entity.GetType();

    // Housekeep
    var castEntityEntry = castDbEntityEntryMethod
        .MakeGenericMethod(new[] { t })
        .Invoke(entityEntry, null);
    housekeepEntityMethod
        .MakeGenericMethod(new[] { t })
        .Invoke(this, new[] { castEntityEntry });

    return base.ValidateEntity(entityEntry, items);
}

private void HousekeepEntity<TEntity>(DbEntityEntry<TEntity> entity)
    where TEntity : class
{
    var housekeeper = DbConfiguration.DependencyResolver.GetService<IHousekeeper<TEntity>>();
    if (housekeeper != null)
    {
        housekeeper.Maintain(entity);
    }
}

我一直在IComponentContext周围传递，所以我可以在那里解析类型，但是使用EF6我希望使用依赖注入：

private class AutofacDbDependencyResolver : AutofacWebApiDependencyResolver, IDbDependencyResolver
{
    public AutofacDbDependencyResolver(ILifetimeScope container)
        : base(container)
    {
    }

    public object GetService(System.Type type, object key)
    {
        using (var scope = this.GetRequestLifetimeScope())
        {
            if (scope == null)
            {
                return null;
            }

            object service;
            scope.TryResolve(type, out service);
            return service;
        }
    }

    public System.Collections.Generic.IEnumerable<object> GetServices(System.Type type, object key)
    {
        using (var scope = this.GetRequestLifetimeScope())
        {
            if (scope == null)
            {
                return System.Linq.Enumerable.Empty<object>();
            }

            object service;
            if (scope.TryResolve(type, out service))
            {
                return new object[] { service };
            }
            else
            {
                return System.Linq.Enumerable.Empty<object>();
            }
        }
    }
}

设置容器时：

System.Data.Entity.DbConfiguration.Loaded += (s, e) =>
    e.AddDependencyResolver(new AutofacDbDependencyResolver(container), overrideConfigFile: false);

但是我的生命周期范围返回null。如何获取调用此操作的当前API请求？

Answer 1

阻止在DbContext中使用service locator anti-pattern。 EF6现在允许你解决它并不重要，它仍然是一种反模式。相反，只需使用依赖注入或允许通过挂钩事件来添加此内务处理。例如，您可以为实体编写部分类：

public partial class MyEntities
{
    public event Action<DbContext> SavingChanges = _ => { };

    public override int SaveChanges()
    {
        this.SavingChanges(this);

        return base.SaveChanges();
    }
}

通过这种方式，您可以简单地抓住当有人拨打SavingChanges时会引发的SaveChanges事件：

builder.Register<MyEntities>(context =>
{
    var db = new MyEntities();
    db.SavingChanges += context.Resolve<IHouseKeepingService>().HousekeepEntities;
    return db;
}).InstancePerLifetimeScope();

Web API上使用Autofac进行EF的依赖注入

1 个答案: