How to combine a query of the LINQ and a list?

Question

[Sorry if it is a duplicate] I couldn't find properly solution, so I decided to ask a question.

I have an object companies which returns list of elements.

I would like to write a query which will select these all CompanyId which we have in our list. I don't want to select only one record by using FirstOrDefault().

Example:

var companiesSummary = _context.Company
                       .Where(c => c.CompanyId == companies.Select(cs => cs.ID))
                       .Include(country => country.Country)

How can I cope with it? Do you have any ideas?

Have you tried it the other way round? e.g.; `from c in companies... etc.`? — Stefan, Jun 10 '18 at 14:25
do you want to query all the Companies where there `id` is in `companies.Select(cs => cs.ID)` or ? — Ousmane D., Jun 10 '18 at 14:25
Thanks guys for the answers. @Stefan in my case it will not give the expected result. — Piotr Podyma, Jun 10 '18 at 14:35

score 1 · Accepted Answer · edited Jun 10 '18 at 14:35

1

Select the ids of the companies from your in-memory list and then pass that into the query in the where method:

var ids = companies.Select(cs => cs.ID).ToList();
var companiesSummary = 
    _context.Company
    .Where(c => ids.contains(c.ID))
    .Include(country => country.Country)

edited Jun 10 '18 at 14:35

Camilo Terevinto

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answered Jun 10 '18 at 14:31

CodingYoshi

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I tried to find how should I solve it, but without expected result. This is what I was looking for, thank you. :-) – Piotr Podyma Jun 10 '18 at 14:51

Tsahi Asher · Answer 2 · 2018-06-10T14:47:26.813

0

Assuming your companies contains a list of objects with an ID property you want to compare to Company.CompanyId, your query should look like

int[] ids = companies.Select(cs => cs.ID).ToArray();
var companiesSummary = _context.Company
    .Where(c => ids.Contains(c.CompanyId))
    .Include(company => company.Country);

edited Jun 10 '18 at 14:47

answered Jun 10 '18 at 14:32

Tsahi Asher

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George Helyar · Answer 3 · 2018-06-10T14:35:54.300

-1

var matchingCompanies = companies.Where(c => companyIds.Contains(c.Id))

Make companyIds a HashSet<T> for an efficient Contains.

edited Jun 10 '18 at 14:35

answered Jun 10 '18 at 14:32

George Helyar

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"Make companyIds a HashSet for an efficient Contains.", why? This will be translated to SQL, it makes absolutely no difference what's the type of `companyIds` – Camilo Terevinto Jun 10 '18 at 14:34
The question does not say it will be converted to SQL, but thanks for the downvote – George Helyar Jun 10 '18 at 14:37
The use of `Include` is clearly from Entity Framework, just as the use of `_context.Company`. – Camilo Terevinto Jun 10 '18 at 14:38
The question never mentions entity Framework, and context is a very common variable name. – George Helyar Jun 10 '18 at 14:39

How to combine a query of the LINQ and a list?

3 Answers3