Linq to query results of list of objects based on another list

Question

I have a list of numbers as shown below:

1) List<long> list1 : 101, 102, 103

And I have a list of Objects, in which one property is long:

2) List<SomeObject> list2: 
   SomeObject[0]- (long)Id : 101,
                  Name: Adam,
                  Address:xxx
   SomeObject[1]- (long)Id : 102,
                  Name: Bran,
                  Address:xxx
   SomeObject[2]- (long)Id : 109,
                  Name: Queen,
                  Address:yyy

I want to query the second list if it has Id's present in list1. Meaning I should get list containing :

SomeObject[0]  
SomeObject[1]

Tried the code below with no success:

(from t2 in list2
          where list1 .Any(t => t2.Id.Contains(t)) == true
          select t2);

Thanks in advance.

Community · Accepted Answer · 2017-05-23 10:30:43Z

5

You can use Enumerable.Contains:

var query = from t2 in list2
            where list1.Contains(t2.Id)
            select t2;

if the values in list1 are uniqe you can also use the more efficient Join:

var query = from t2 in list2
            join t1 in list1
            on t2.Id equals t1
            select t2;

Your approach doesn't work:

where list1.Any(t => t2.Id.Contains(t)) == true

because t2.Id returns a long which has no Contains method.

If you wanted to use Any you could use this:

where list1.Any(t => t2.Id == t)

edited May 23, 2017 at 10:30

CommunityBot

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answered Jul 5, 2016 at 11:46

Tim Schmelter

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2 Comments

Lumen Over a year ago

Maybe you can also explain why the OP’s approach did not work. He did use Contain, after all.

Ivan Yurchenko Over a year ago

@TimSchmelter t is also a long but he doesn't check Id for t. He checks Id for t2 that is SomeObject which has Id.

juharr · Accepted Answer · 2016-07-05 11:53:15Z

1

The issue with your query is that you are trying to call Contains on a long. Instead it should have been list1 .Any(t => t2.Id == t). But instead you can just do a join.

from t1 in list1
join t2 in list2 on t1 equals t2.Id
select t2

edited Jul 5, 2016 at 11:53

answered Jul 5, 2016 at 11:46

juharr

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Comments

Abhilash R Vankayala · Accepted Answer · 2016-07-05 11:59:36Z

1

You can also use the below code snippet to get the desired result, where

var result = list2.Where(l2 => list1.Any(l1 => l1 == l2.Id));

answered Jul 5, 2016 at 11:59

Abhilash R Vankayala

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