强制转换数据库集<T>和调用方法

Question

我正试图编写一个方法，将属性强制转换为DbSet，然后调用load方法。

我尝试过以下几种：

var value = propertyInfo.GetValue(em, null) as DbSet;
//Not working, because it always returns null
var value = propertyInfo.GetValue(em, null) as DbSet<T>;
//Not working, because its a syntax error and doesnt even compile (giving error 'Cannot resolve symbol T')
var value = propertyInfo.GetValue(em, null) as DbSet<TEntity>;
//Not working, because its a syntax error and doesnt even compile (giving error 'Cannot resolve symbol TEntity')

但只有当我指定正确的类型时，它才能工作：

var value = propertyInfo.GetValue(em, null) as DbSet<TempTable>;

如何在不指定TempTable的情况下解决此问题？

Answer 1

var value = propertyInfo.GetValue(em, null) as DbSet;
//Not working, because it always returns null

的确；DbSet<TEntity>不是从DbSet继承的，所以是的，它将始终是null。

//Not working, because its a syntax error and doesnt even compile (giving error 'Cannot resolve symbol T')

你需要知道与之交谈的东西的类型；您可以使用非通用的IEnumerable/IQueryable API，但我怀疑这里最合适的错误可能是dynamic:

dynamic val = propertyInfo.GetValue(em, null);
EvilMethod(val);
//...
void EvilMethod<T>(DbSet<T> data)
{
    // this will resolve, and you now know the `T` you are talking about as `T`
    data.Load();
}

或者如果您只是想调用Load:

dynamic val = propertyInfo.GetValue(em, null);
val.Load();

Answer 2

试试这个：

var value = propertyInfo.GetValue(em, null) as IQueryable;
value.Load();

Answer 3

可能是这样的：

var setMethod = typeof(MyDataContext)
    .GetMethods(BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.Instance)
    .Where(m => m.Name == "Set")
    .Where(m => m.IsGenericMethod)
    .Select(m => m.MakeGenericMethod(typeof(TEntity)))
    .SingleOrDefault();
var value = setMethod.Invoke(myDataContextInstance, null);