linq - Concatenating Two Different IEnumerable Objects in C# -

i have got 2 different ienumerable objects, properties similar in both classes,now want concatenate/merge them, both results can assigned repeater datasource, below sample code.

ienumerable<icacheditem> cacheold = cache<string>.cacheditems; //my old cache class, here fetching cached items ienumerable<caching.icacheditem> cachenew = caching.cache<string>.cacheditems; //my new class cached items    var combined = cachenew.cast<icacheditem>().concat(cacheold); //trying concat both repeater.datasource = combined.orderby(entry => entry.region + ":" + entry.prefix + ":" + entry.key); //assigning datasource repeater.databind(); 

combined object coming blank, suggestions.

update: have got these in class

public class cacheditem<t>: icacheditem {      public cacheditem(string key, string prefix, t value)         : this(cacheregion.site, prefix, key, value)     {     }     } 

do need modify class?

you can use select convert new items old items. assuming have appropriate constructor, can this:

var combined = cachenew.select(newitem => new oldcacheditem(newitem)).concat(cacheold); 

the result of type ienumerable<icacheditem>. should replace oldcacheditem name of old cached item type implements icacheditem.