How to merge two IQueryable lists

Question

I want to merge the records of two IQueryable lists in C#. I try

IQueryable<MediaType> list1 = values; IQueryable<MediaType> list2 = values1; obj.Concat(obj1); 

and

IQueryable<MediaType> list1 = values; IQueryable<MediaType> list2 = values1; obj.Union(obj1); 

but if list1 is empty then the resultant list is also empty. In my case either list1 can be empty but list2 can have records. How should i merge them?

Answer 1

You're not using the return value - just like all other LINQ operators, the method doesn't change the existing sequence - it returns a new sequence. So try this:

var list3 = list1.Concat(list2); 

or

var list4 = list1.Union(list2); 

Union is a set operation - it returns distinct values.

Concat simply returns the items from the first sequence followed by the items from the second sequence; the resulting sequence can include duplicate items.

You can think of Union as Concat followed by Distinct.

Answer 2

Even

var result = Enumerable.Concat(list1, list2); 

doesn't work?

And be sure that lists are empty, not null:

var result = Enumerable.Concat(     list1 ?? Enumerable.Empty<MediaType>()     list2 ?? Enumerable.Empty<MediaType>()); 

Also try:

var result = Enumerable.Concat(     list1.AsEnumerable(),     list2.AsEnumerable());