如何将IEnumerable（没有类型）转换为IQueryable <T>？

Question

Having used LINQ quite a bit I am stumbling over a basic task today:

Having an IQueryable<T> out of an IEnumerable (without a type specified).

Specifically I want to query over parameters of an SqlParameterCollection . This is deriving from IDataParameterCollection, IList, ICollection, IEnumerable as described here . However, these are all without the type specified.

Thus my question boils down to: How to use LINQ to query over an SqlParameterCollection?

Here's what I have done (the compiler did not complain):

IQueryable<SqlParameter> queryable = 
    sqlCommand.Parameters.AsQueryable().Cast<SqlParameter>();
    //throws ArgumentException "source is not IEnumerable<>"

Note: I have searched quite a bit, but everyone is talking about IEnumerable<T> which is fairly easy to query using AsQueryable() of course.

Answer 1

I am interested in the reason why you want to do this. This should do what you explained:

public IQueryable<T> AsQueryable<T>(IEnumerable list)
{
    return list.Cast<T>().AsQueryable();   
}

Call like this:

IQueryable<SqlParameter> query = AsQueryable<SqlParameter>(sqlParameterCollection);