How to merge two IQueryable lists

c# iqueryable
Fraz Sundal picture Fraz Sundal · Oct 23, 2010 · Viewed 45.6k times · Source

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

Jon Skeet picture Jon Skeet · Oct 23, 2010

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.

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