Catch in IEnumerable Yield

Find.cs

// why this do not work?

public IEnumerable<T> Find(Query query)
{
    while(true)
    {
        try
        {
            // FindWrap returns IEnumerable using yield return
            return FindWrap(query);
        }
        catch(IndexNotFoundException ex)
        {
            // never run this!!
            this.EnsureIndex(ex);
        }
        catch(Exception ex)
        {
            // doesn't works here too
        }
        finaly
        {
            // where it's ok
        }
    }
}

I wrote this:

while (true)
{
    var enumerable = _engine.Value.Find(_name, query, skip, limit);
    var enumerator = enumerable.GetEnumerator();

    for (bool more = true; more;)
    {
        // Catch exceptions only on executing/resuming the iterator function
        try
        {
            more = enumerator.MoveNext();
        }
        catch (IndexNotFoundException ex)
        {
            this.EnsureIndex(ex);

            enumerable = _engine.Value.Find(_name, query, skip, limit);
            enumerator = enumerable.GetEnumerator();
            continue;
        }

        // executing all includes in BsonDocument
        foreach (var action in _includes)
        {
            action(enumerator.Current);
        }

        // get object from BsonDocument
        var obj = _mapper.ToObject<T>(enumerator.Current);

        yield return obj;
    }

    if (enumerator != null) enumerator.Dispose();
}

Work for IEnumerable/Catch exception but it's not valid in this case: locking problems (as #399).