遍历派生的DbContext DbSet，以便可以向我的DbContext对象添加ClearAll（）扩展 [英] Looping over derived DbContext DbSets so I can add a ClearAll() extension to my DbContext object

问题描述

基于[ Type.IsGenericType 与 Type.IsGenericTypeDefinition 之间的区别] [1]，我获得了为了能够通过反射检索DbContext的DbSet，我缺少了一条信息。

Based on [the difference between Type.IsGenericType and Type.IsGenericTypeDefinition][1], I gained the piece of information I was missing in order to be able to retrieve a DbContext's DbSets via Reflection.

但是，我现在被困在其他地方。在下面的代码示例中，我确实成功获取了DbSet泛型实例，但是现在我希望能够在编译时将其强制转换为特定的泛型类型定义。

However, I am now stuck somewhere else. In the code sample below, I do succeed in obtaining the DbSet generic instances, but I now want to be able to cast them at compile time, to the specific generic type defintion.

dbSet是我的DbContext中DbSets< ...>之一的真实实例，但是如何将其转换为实型定义？ （在第一个循环迭代中，dBSet将代表DbSet-如何在编译时对该变量执行此类型？

dbSet is a real instance of one of the DbSets<...> from my DbContext, but how to cast it to its real type definition ? (Take the 1st loop iteration, dBSet will represent DbSet - how to enforce this type at compile time upon this variable ?

更新：我刚刚回顾了我要尝试做的事情，...这恐怕是没有意义的/不可能的。由于实际类型只能在运行时发现，因此我无法在此之前（并且编译时间是在此之前的时间）可以与真正的泛型类型相关。

Update: I have just reviewed what I am trying to do and... am afraid it makes no sense/it is not possible. Since the real types are discovered only at runtime, there is no way I can, prior to that (and compile time is a stage in time prior to that) relate to the real generic types.

无论如何-我真正感兴趣的是是要在编译时向IDE显示 IEnumerable< T> 的成员（DbSet<>实现了它），所以我真的需要将其强制转换为 DbSet<> 。这样的转换应如何显示？

In any case - what I am really interested to is to have, at compile time, the IDE showing me members of IEnumerable<T> (DbSet<> implements it). So I really need to cast it to DbSet<>. How does such a cast should look like ?

有可能吗？！

private static void Main(string[] args)
{
    MyDb myDb = new MyDb();

    List<PropertyInfo> dbSetProperties = myDb
        .GetType()
        .GetProperties()
        .Where(pi => pi.PropertyType.IsGenericType && string.Equals(pi.PropertyType.GetGenericTypeDefinition().FullName, typeof(DbSet<>).FullName, StringComparison.OrdinalIgnoreCase)).ToList();

    foreach (PropertyInfo dbSetProperty in dbSetProperties)
    {
        Type[] typeArguments = dbSetProperty.PropertyType.GetGenericArguments();
        Type dbSetGenericContainer = typeof(DbSet<>);
        Type dbSetGenericType = dbSetGenericContainer.MakeGenericType(typeArguments);
        object dbSet = Convert.ChangeType(dbSetProperty.GetValue(myDb), dbSetGenericType);
    }
}

public class MyDb : DbContext
{
    public DbSet<A> A { get; set; }
    public DbSet<B> B { get; set; }

    public void ClearTables()
    {
    }
}

public class A
{
    public string aaa { get; set; }
    public List<int> myList { get; set; }
}

public class B
{
    public int MyInt { get; set; }
}

推荐答案

DbSet<> 本身不是类型；您的问题实际上没有任何意义。

DbSet<> itself is not a type; your question doesn't actually make sense.

但是，幸运的是， DbSet&T; 实现了非-generic DbSet 基类，因此您可以改用它。

However, luckily for you, DbSet<T> implements the non-generic DbSet base class, so you can just use that instead.

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