Create a Tuple in a Linq Select

Question

I'm working with C# and .NET Framework 4.5.1 retrieving data from a SQL Server database with Entity Framework 6.1.3.

I have this:

codes = codesRepo.SearchFor(predicate)
      .Select(c => new Tuple<string, byte>(c.Id, c.Flag))
      .ToList();

And when I run it, I get this message:

Only parameterless constructors and initializers are supported in LINQ to Entities.

I don't know how I have to create the Tuple because all the examples that I have found are mostly like this one.

I have tried this:

codes = codesRepo.SearchFor(predicate)
      .Select(c => Tuple.Create(c.Id, c.Flag))
      .ToList();

And get this error:

LINQ to Entities does not recognize the method 'System.Tuple`2[System.String,System.Byte] Create[String,Byte](System.String, Byte)' method, and this method cannot be translated into a store expression.

Where is the problem?

Looks like you'll need to create a strongly typed object. But yes, good question; upvoted. — frenchie
– frenchie, Commented Nov 5, 2015 at 13:05

Ivan Stoev · Accepted Answer · 2019-07-09 11:50:22Z

190

While the answer by octavioccl works, it's better to first project the query result into anonymous type, and then switch to enumerable and convert it to tuple. This way your query will retrieve from the data base only the fields needed.

codes = codesRepo.SearchFor(predicate)
    .Select(c => new { c.Id, c.Flag })
    .AsEnumerable()
    .Select(c => new Tuple<string, byte>(c.Id, c.Flag))
    .ToList();

Note: The above rule applies to EF6. EF Core naturally supports tuples (in projection or as join/group keys) via tuple constructor, e.g. the original query simply works

codes = codesRepo.SearchFor(predicate)
  .Select(c => new Tuple<string, byte>(c.Id, c.Flag))
  .ToList();

but not the Tuple.Create method (EF Core 2.x).

edited Jul 9, 2019 at 11:50

answered Nov 5, 2015 at 13:18

Ivan Stoev

208k17 gold badges356 silver badges376 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

skyfrog Over a year ago

Very good solution - Thanks! ... What about if I'd had to extend this solution by another nullable value? .Select(c => new { c.Id, c.Flag, c.Foo?.Code }) does not work.

Ivan Stoev Over a year ago

@skyfrog The operator ?. is not supported in expression trees. But other than that, you can extend the anonymous type with as many values you want - just don;t forget to name them when needed :) e.g. c => new { c.Id, c.Flag, Code = (int?)c.Foo.Code }

skyfrog Over a year ago

Great! Many thanks @Ivan for your reply. I was so close! ... but it is always easy to say while looking back ;-)

joedotnot Over a year ago

Great answer, can be used with EF-Entities.. e.g. dbCtx.MyEntity.Where().Select( .. to anon object...).etc...

Honza P. Over a year ago

Just a note, Linq does not accept named Tuple in my case, but I can live with that. This approach works sufficiently in my case.

Eric D. Johnson · Accepted Answer · 2020-09-14 16:33:08Z

107

Just an updated answer for C# 7, now you can use a simpler syntax to create ValueTuples.

codes = codesRepo.SearchFor(predicate)
.Select(c => new { c.Id, c.Flag })
.AsEnumerable()
.Select(c => (c.Id, c.Flag))
.ToList();

You can even name the properties of the tuple now:

codes = codesRepo.SearchFor(predicate)
.Select(c => new { c.Id, c.Flag }) // anonymous type
.AsEnumerable()
.Select(c => (Id: c.Id, Flag: c.Flag)) // ValueTuple
.ToList();

So instead of using it as Item1 or Item2 you can access it as Id or Flag.

More docs on choosing-between-anonymous-and-tuple

edited Sep 14, 2020 at 16:33

Eric D. Johnson

11.9k11 gold badges43 silver badges48 bronze badges

answered Nov 27, 2018 at 3:46

Rafael Merlin

2,7872 gold badges27 silver badges32 bronze badges

Comments

Dhunt · Accepted Answer · 2015-11-05 13:18:40Z

17

Try this:

codes = codesRepo.SearchFor(predicate)
  .Select(c => Tuple.Create(c.Id, c.Flag))
  .ToList();

Been informed this isn't accepting in LINQ to entities.

Another option would be to pull the result into memory before selecting. If you are going to do this I would recommend doing all of the filtering before the .AsEnumerable() as it means you are only pulling back results that you want as opposed to pulling back the whole table and then filtering.

codes = codesRepo.SearchFor(predicate).AsEnumerable()
  .Select(c => Tuple.Create(c.Id, c.Flag))
  .ToList();

as well Tuple.Create(c.Id, c.Flag) could be changed to new Tuple(c.Id, c.Flag) if you want to make the code a bit more explicit in the tuples types

edited Nov 5, 2015 at 13:18

answered Nov 5, 2015 at 13:06

Dhunt

1,5949 silver badges22 bronze badges

1 Comment

VansFannel Over a year ago

Sorry, it doesn't work. I have updated my question with more details.

Community · Accepted Answer · 2017-05-23 11:54:53Z

12

In linq to entities you can project onto an anonymous type or onto a DTO.To avoid that issue you can use AsEnumerable extension method:

codes = codesRepo.SearchFor(predicate).AsEnumerable().
      .Select(c => new Tuple<string, byte>(c.Id, c.Flag))
      .ToList();

This method lets you work with Linq to Object instead Linq to Entities, so after call it,you can project the result of your query in whatever you need.The advantage of using AsEnumerable instead ToList is that AsEnumerable does not execute the query, it preserves deferred execution. It's good idea always filter your data first before call one of these methods.

edited May 23, 2017 at 11:54

CommunityBot

11 silver badge

answered Nov 5, 2015 at 13:06

ocuenca

39.5k12 gold badges95 silver badges107 bronze badges

1 Comment

Aron Over a year ago

-1 This does not do the same thing as was asked by the OP. Sometimes, being able to create Tuples in a query, for Joining purposes is important.

Mohammad Soori · Accepted Answer · 2018-02-22 08:35:13Z

1

Use this method to do this and use the async.

var codes = await codesRepo.SearchFor(predicate)
                    .Select(s => new
                    {
                        Id = s.Id,
                        Flag = s.Flag
                    }).FirstOrDefaultAsync();

                var return_Value = new Tuple<string, byte>(codes.Id, codes.Flag);

answered Feb 22, 2018 at 8:35

Mohammad Soori

2,4181 gold badge20 silver badges17 bronze badges

Comments

IbrarMumtaz · Accepted Answer · 2019-01-16 10:33:37Z

0

Just my two cents: this has caught me out a few times with the type names:

A few noddy examples:

    private Tuple<string, byte> v1()
    {
        return new Tuple<string, byte>("", 1);
    }

    private (string, int) v2()
    {
        return ("", 1);
    }

    private (string Id, byte Flag) v3()
    {
        return ("", 1);
    }

Regards.

edited Jan 16, 2019 at 10:33

answered Jan 10, 2019 at 10:22

IbrarMumtaz

4,45210 gold badges48 silver badges66 bronze badges

3 Comments

M.Stramm Over a year ago

The syntax you posted does not work. What you probably meant to write is public (string Id, byte Flag) SearchFor(Expression predicate), but this is beside the point. Two cents shouldn't be an answer, but a comment.

IbrarMumtaz Over a year ago

I updated my answer - i should have checked it before posting. I disagree; all info is useful to all visitors who land on this page regardless how it is posited. Comments do not convey intent as well as answer thanks to answers.

M.Stramm Over a year ago

I do agree that added content is good and comments don't cater well to code examples. Thanks for editing, now it is clear that this is not an answer to the OP's question (but may help with tuple related problems).

Jaider · Accepted Answer · 2023-05-14 05:11:02Z

-1

You also can use record.

https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/records

private record Code(string Id, byte Flag);

then use it like

codes = codesRepo.SearchFor(predicate)
      .Select(c => new Code(c.Id, c.Flag))
      .ToList();

later you can use a named property instead of a .Item1, .Item2

var code = codes.First();
...code.Id; 
...code.Flag;

answered May 14, 2023 at 5:11

Jaider

15.1k5 gold badges83 silver badges88 bronze badges

3 Comments

Gert Arnold Over a year ago

That defeats the purpose of creating a Tuple: not having to define a named structure. Also, tuples do have named members since a couple of years.

Jaider Over a year ago

@gert-arnold-is-on-strike Named tuples is not supported on linq-sql. so you have to do a select with anonymous to read, materialize (asEnumerable, toList, etc), and then another select for named tuples... which it is cumbersome. In Linq-SQL, I tends to use a lot of anonymous type, or some classes or records, but I try to avoid tuples for the reason above.

Gert Arnold Over a year ago

Sure, it's awkward, but it's a way to return fixed-format typed data from a method w/o having to define a class/struct etc. I think that's OP's purpose.

Collectives™ on Stack Overflow

Create a Tuple in a Linq Select

7 Answers 7

5 Comments

Comments

1 Comment

1 Comment

Comments

3 Comments

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

5 Comments

Comments

1 Comment

1 Comment

Comments

3 Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related