IEnumerable到T []的数组

Question

问题标题可能不正确.我有以下变量

IEnumerable x = // some IEnumerable
System.Type y = // some type

如何迭代x以生成具有y类型项的数组？

当我查看互联网时,我发现:

public T[] PerformQuery<T>(IEnumerable q)
{                         
        T[] array = q.Cast<T>().ToArray();
        return array;
}

注意我不能调用那个方法,因为PerformQuery y是类型的System.Type,换句话说就是调用它PerformQuery<typeof(y)>(x);或者PerformQuery<y>(x);会给我一个编译器错误.

---

编辑

这就是我遇到这个问题的原因.我有网络服务,我发布了两件事.我想要查询的表的类型(示例typeof(Customer)),以及实际的字符串查询示例"Select*from customers"

    protected void Page_Load(object sender, EventArgs e)
    {
        // code to deserialize posted data
        Type table = // implement that here
        String query = // the query that was posted

        // note DB is of type DbContext
        IEnumerable q = Db.Database.SqlQuery(table, query );

        // here I will like to cast q to an array of items of type table!

Answer 1

您可以使用表达式树:

public static class MyExtensions
{
    public static Array ToArray(this IEnumerable source, Type type)
    {
        var param = Expression.Parameter(typeof(IEnumerable), "source");
        var cast = Expression.Call(typeof(Enumerable), "Cast", new[] { type }, param);
        var toArray = Expression.Call(typeof(Enumerable), "ToArray", new[] { type }, cast);
        var lambda = Expression.Lambda<Func<IEnumerable, Array>>(toArray, param).Compile();

        return lambda(source);
    }
}

它x => x.Cast<Type>().ToArray()为您生成,Type在运行时已知.

用法:

IEnumerable input = Enumerable.Repeat("test", 10);
Type type = typeof(string);

Array result = input.ToArray(type);

Answer 2

var ObjectsOfType_y = x.OfType<object>().Where(x => x.GetType() == y);

但请注意，这将返回一个IEnumerable<object>。没有办法解决这个问题，因为y(Type) 表示的类型在编译时是未知的。