Look at either Multisearch

http://world.episerver.com/documentation/Items/Developers-Guide/EPiServer-Find/9/DotNET-Client-API/Searching/Multiple-searches-in-one-request/

or

search over multiple types

http://world.episerver.com/documentation/Items/Developers-Guide/EPiServer-Find/9/DotNET-Client-API/Searching/Searching-over-multiple-types/

Both of this will only support GetResult so you will not get a page reference. But if I am not wrong if you use getcontentresult to get content EPiServer will do a request to database if it does not have it in cache so if you are looking into performace, you should look into projecting into a type that you can use all the way so you wont need to call the database at all.

How about something like this:

                var result = SearchClient.Instance.Search<PageData>()
                    .Filter(x => ((EventPage) x).DateAndTime.After(DateTime.Now))
                    .Filter(x => x.MatchType(typeof (EventPage)) | x.MatchType(typeof (ExternalEventPage)))
                    .GetContentResult();

This should return EventPages and ExternalEventPages as PageData, so you'll need to check the results orginal type. Don't worry about the EventPage cast. The filter will work even though ExternalEventPage cannot be casted to EventPage. 

As Henrik mentions, GetContentResult will fetch the page using the content loader. However, you should not be worried about that as the pages will be cached.

Per Magne, will this line work if not Eventpage is basepage of ExternalEventPage?

.Filter(x => ((EventPage) x).DateAndTime.After(DateTime.Now))

You are correct about caching, it should work ok.

@Henrik, it will work. When the code is executed, the cast will never actually be done. All that Find care about is the property name, which is "DateAndTime". 

@Henrik,

I tried http://world.episerver.com/documentation/Items/Developers-Guide/EPiServer-Find/10/DotNET-Client-API/Searching/Searching-over-multiple-types/ but obviously I'm doing something wrong as I`m getting 0 hits:

var searchQuery = SearchClient.Instance.Search<EventViewModel>()
                                .Filter(x => x.DateAndTime.After(DateTime.Now));

// TODO: dynamic filters

searchQuery.IncludeType<EventViewModel, EventPage>(x => new EventViewModel
{

    DateAndTime = x.DateAndTime,
    Location = x.Location,
    // rest of the fields
    IsExternal = false
}).IncludeType<EventViewModel, ExternalEventPage>(x => new EventViewModel
{
    DateAndTime = x.DateAndTime,
    Location = x.Location,
    // rest of the fields
    IsExternal = true
});

var result = searchQuery.OrderBy(x => x.DateAndTime)
                        .Skip((pageNumber - 1) * pageSize)
                        .Take(pageSize)
                        .GetResult();

@Per,

I want to avoid GetContentResult() as I`m using CQRS approach to index data that is optimized for search. I want to prepare data / do calculations only once (on page publishing event), instead of doing it every time on search results page.

the IncludeType filtering is not being added. You need to assign it to a new variable.

var searchQuery2 = searchQuery.IncludeType<....

or include it in your original query

Thank you guys! Works like a charm!

Thanks Per Magne, I did not know Find worked that way.

Dejan, I have done exactly the same error many times and then trying to found out why it is not working when it all looks good.... Just a little variable = variable...... :)

Glad to help and glad that i works!

I know this is already marked as answered. Bur if your page types shares the same properties, why not use a base class or interface and then search for that type instead?

I agree with Johan. Using an interface would be probably make the code a bit cleaner.

I need to display 4-5 fields from one page type (properties + some pre-calculated data) and 4-5 fields from the other one. Only 2 fields (Location and Date) are common, so I can create an interface for that, but how can I use it to create projections?

I'd like to avoid a call to GetPagesResult / GetContentResult.

Thanks for help!