Why does this LinQ query not like chars?

Question

I have a LINQ query that grabs all the data it needs and consolidates it into a data transfer object, everything works fine EXCEPT it throws query exceptions when I set one of the DTO's members (which is a char) to a char value...

An unhandled exception of type 'System.ServiceModel.FaultException' occurred in mscorlib.dll

Unable to create a constant value of type 'System.Char'. Only primitive types or enumeration types are supported in this context.

See the simplified query below:

var result = (from c in db.Foster_Carers
              where c.foster_carer_id == id
              join fc in db.Individual_Carers on c.first_carer_id equals fc.individual_carer_id
              select new FosterCarerPersonalInfoDTO
              {
                  carer_title = fc.title,
                  carer_forenames = fc.forename,
                  carer_surname = fc.surname,                                
                  carer_gender = 'm'
              }).SingleOrDefault();

Setting the gender to 'm' just won't work, syntactically it is okay, just not when the query is executed! What could be the issue?

Are you sure that `carer_gender` not throws custom exception in property implementation when one sets 'm' there? — Ryszard Dżegan, Sep 26 '13 at 10:28
@MarcGravell - Sorry I forgot include that in the Q, the exception thrown is - _An unhandled exception of type 'System.ServiceModel.FaultException' occurred in mscorlib.dll_ — Sam, Sep 26 '13 at 10:30
Please post ToString() of this exception so that we can see inner details. — Pavel Tupitsyn, Sep 26 '13 at 10:32
`FaultException` would indicate it's an issue going across the wire, not an issue with LINQ. It's worth posting your WCF method. — James, Sep 26 '13 at 10:37
Further exception info (just had to switch the service into debug mode to get this) - Additional information: Unable to create a constant value of type 'System.Char'. Only primitive types or enumeration types are supported in this context. — Sam, Sep 26 '13 at 10:41
@James - yeahh, learning on the fly ;) for the sake of what I am doing I can easily switch the DTO property to string, but I would like to know why this won't work... and not surrender to this issue! — Sam, Sep 26 '13 at 10:47
@James - just saw your edit! Ohhh okay, pfttt what a strange issue! I did research prior to posting this question however it would have helped if I had got the _real_ exception information earlier (like you said). Thanks for the help, If you would like to post an answer stating the issue I would be happy to accept it :) Thanks again — Sam, Sep 26 '13 at 10:52
@Sam I just made my comment an answer - "Convert to answer" feature on the comments? Might post that on meta :) — James, Sep 26 '13 at 10:55
The query provider doesn't support it. See James' answer below... — Gayot Fow, Sep 26 '13 at 13:18
@GarryVass - yeahh I had already accepted that answer, thanks though :) — Sam, Sep 26 '13 at 13:34

score 7 · Accepted Answer · edited May 23 '17 at 10:29

7

This is a limitation of EF because char is not a primitive type, see this answer for more details as to why. The limitation itself is also documented.

I would suggest you just use string.

edited May 23 '17 at 10:29

Community

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answered Sep 26 '13 at 10:54

James

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Interesting fact. Thanks for the link to the documentation. – Matt Becker Apr 14 '15 at 19:31

Stephen Turner · Answer 2 · 2014-09-26T12:55:50.807

I've come across the same and had to store an intermediate value and do a conversion outside of the Linq query:

var intermediateResult = (from c in db.Foster_Carers
          where c.foster_carer_id == id
          join fc in db.Individual_Carers on c.first_carer_id equals fc.individual_carer_id
          select new 
          {
              oldResult = new FosterCarerPersonalInfoDTO
              {
                  carer_title = fc.title,
                  carer_forenames = fc.forename,
                  carer_surname = fc.surname,                                
              }
          ,   forConversion = new
              {
                  carer_gender = "m"
              }
          }).SingleOrDefault();

intermediateResult.oldResult.carer_gender = intermediateResult.forConversion.carer_gender[0];

var result = intermediateResult.oldResult;

score 0 · Answer 3 · answered Apr 24 '20 at 15:24

If this is coming from VS and MVC using c# then Get rid of the apostrophe's and use full quotation marks instead.

use

carer_gender = "m"

instead of

carer_gender = 'm'

I've found that C# interprets the single quote as a char type instead of string.

In my case I had

var _list = (from a in table where string.Concat(a.AbsenceReasonCodeID, "|", a.Description).ToUpper().Contains(vlsTerm) select new { value = a.field1, label = String.Concat(a.field1, " : ", a.field2) }).ToList();

When I used single quotes I got the char error. Replacing them with double got rid of the problem.

Why does this LinQ query not like chars?

3 Answers3

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