linq distinct and select new query

Question

I have a query

var QP = (from a in QProductAllInfo select new { a.Id, a.Title, a.FullTitle}).Distinct();

Result is:

• 1 Ivanov Ivan
• 1 Ivanov Ivan
• 2 Petrov Petr
• 3 Sidorov Ivan
• 3 Sidorov Ivan

and i need result:

• 1 Ivanov Ivan
• 2 Petrov Petr
• 3 Sidorov Ivan

Answer 1

Assuming that different Ids are always considered distinct you can try this.

I would probably write it in two querys. That way it is easy to debug and more readable. You can use MoreLinq.

DistinctBy

Download

var temp = from a in QProductAllInfo select new { a.Id, a.Title, a.FullTitle}.ToList();

var result = temp.DistinctBy(i => i.Id);

You can also use

Var result = temp.GroupBy(x => x.Id).Select(y => y.First());

Answer 2

If you have duplicates in QProductAllInfo, replacing your code by this should fix your problem.

var QP = from a in QProductAllInfo.Distinct() 
         select new { a.Id, a.Title, a.FullTitle };

if this doesn't work, you can use tuples instead of anonymous types like this:

var QP = from a in QProductAllInfo
         select Tuple.Create(a.Id, a.Title, a.FullTitle);

Applying the Distinct operator on anonymous types is useless because anonymous types are always reference types that donc implement the IEquatable interface.