Looping over derived DbContext DbSets so I can add a ClearAll() extension to my DbContext object

问题

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.

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 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 ?

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.

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 ?

Is it possible ?!

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; }
}

回答1:

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

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

来源：https://stackoverflow.com/questions/31771628/looping-over-derived-dbcontext-dbsets-so-i-can-add-a-clearall-extension-to-my

标签

reflection

dbset

system.type