Return unique values only in Webapi controller

Question

I have the following line in a WebApi controller;

string Codes = i.Products.FirstOrDefault().Code

As the line states, it gets the code, from the first Product.

But, what I really want it to do is to get all unique codes, and return them as a comma separated string.

So, let's say, there are 6 related products, and they have the following codes:

45
54
45
120
54
45

Right now, the statement just returns "45", given the above data.

But I want the statement above to return "45, 54, 120" (as a string).

How do I do this?

Complete code:

public System.Data.Entity.DbSet<WebAPI.Models.Product> Products { get; set; }
private ApplicationDbContext db = new ApplicationDbContext();

var product = await db.Products.Select(i =>
                new ProductDTO()
                {
                    Id = i.Id,
                    Created = i.Created,
                    Title = i.Title,                    
                    Codes = i.Products.FirstOrDefault().Code

                }).SingleOrDefaultAsync(i => i.Id == id);

Do you need your controller to return a collection of codes or a string concatenation of these codes? — vc 74, Mar 16 '16 at 13:58

Alper Tunga Arslan · Answer 1 · 2016-03-16T14:28:14.433

0

I think Distinctand String.Join works for you.Please try this:

var product = await db.Products.AsEnumerable()//Turn AsEnumarable
.Select(i =>
   new ProductDTO()
   {
     Id = i.Id,
     Created = i.Created,
     Title = i.Title,                    
     Codes = string.Join(",", 
               i.Products.Select(l => l.Code).Distinct())
   }).SingleOrDefaultAsync(i => i.Id == id);

edited Mar 16 '16 at 14:28

answered Mar 16 '16 at 13:55

Alper Tunga Arslan

569
3
10

DistinctBy? Do you mean Distinct? – vc 74 Mar 16 '16 at 13:58
It is extension method for linq. If you want you can look [link](https://code.google.com/archive/p/morelinq/wikis/OperatorsOverview.wiki) – Alper Tunga Arslan Mar 16 '16 at 14:03
thx @AlperTungaArslan But i get an error 'cannot implicitly convert IEnumerable to string (Codes is a string)? – brother Mar 16 '16 at 14:06
I am unsure how i can merge this into my excisting code. I updated my question with some more of my code? – brother Mar 16 '16 at 14:14
I now get 'IEnumerable does not contain a definition for SingleOrDefaultAsync'.. :/ – brother Mar 16 '16 at 15:58
Make sure you have added System.Data.Entity namespace to your usings. This is an extension method, and it will not be available until you add appropriate namespace. @brother – Alper Tunga Arslan Mar 17 '16 at 07:10

vc 74 · Answer 2 · 2016-03-16T14:26:55.927

0

To convert to a comma separated list:

IEnumerable<string> distinctCodes = i.Products.Select(product => product.Code).Distinct();

return string.Join(",", distinctCodes);

But it's probably better if your controller returns a collection of string instead of a concatenated string.

Edit, after OP code update:

var DBProduct = await db.Products.SingleOrDefaultAsync(i => i.Id == id);

IEnumerable<string> productCodes = DBProduct.Products.Select(p => p.Code).Distinct();

var product = new ProductDTO()
{
   Id = DBProduct.Id,
   Created = DBProduct.Created,
   Title = DBProduct.Title,                    
   Codes = string.Join(",", productCodes)
};

edited Mar 16 '16 at 14:26

answered Mar 16 '16 at 14:09

vc 74

37,131
7
73
89

I updated my question, with more of the code. I am unsure how i would incorporate your answer, with my code above? – brother Mar 16 '16 at 14:12
I get this error 'LINQ to Entities does not recognize the method 'System.String Join(System.String, System.Collections.Generic.IEnumerable`1[System.String])' method, and this method cannot be translated into a store expression.' – brother Mar 16 '16 at 14:22
You must turn AsEnumerable before string.join look this [example](http://stackoverflow.com/questions/10079990/linq-to-entities-does-not-recognize-the-method-system-string-formatsystem-stri) – Alper Tunga Arslan Mar 16 '16 at 14:30
I now get 'IEnumerable does not contain a definition for SingleOrDefaultAsync'.. :/ – brother Mar 16 '16 at 15:58

Return unique values only in Webapi controller

2 Answers2