Cannot convert lambda expression to type 'string' because it is not a delegate type

Question

I am using a LINQ lambda expression like so:

int Value = 1;
qryContent objContentLine;

using (Entities db = new Entities())
{
    objContentLine = (from q in db.qryContents
                      where q.LineID == Value
                      orderby q.RowID descending
                      select q).FirstOrDefault();
}

However, I am getting the following error:

Cannot convert lambda expression to type 'string' because it is not a delegate type

Cannot convert lambda expression to type 'string' because it is not a delegate type — Deep Sharma, Oct 05 '13 at 11:53
Can you give more details on the class `qryContent` and on the `db.qryContents` property? — meilke, Oct 05 '13 at 11:55
Where, not which error. In the query? When evaluating it later? Because that code you posted can't produce the error, unless it is in `db.qryContents`. — Femaref, Oct 05 '13 at 11:56
the column i am using LineID is integer type. qryContent is a view in db. — Deep Sharma, Oct 05 '13 at 11:57
http://stackoverflow.com/questions/2058487/entity-framework-cannot-convert-lambda-expression-to-type-string-because-it?rq=1 maybe this will help? — Femaref, Oct 05 '13 at 11:57

score 362 · Accepted Answer · edited Jan 20 '18 at 01:21

362

I think you are missing using System.Linq; from this system class.

and also add using System.Data.Entity; to the code

edited Jan 20 '18 at 01:21

Mr Nobody

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answered Oct 05 '13 at 12:00

S. S. Rawat

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I actually had this issue just a few minutes prior and I had usings for System.Linq and System.Data.Entity. I had to remove them, run a failed build and then readd them to the file. Then it worked. – Pharcyde Jan 13 '21 at 15:21

score 99 · Answer 2 · edited Sep 03 '14 at 14:42

99

In my case, I had to add using System.Data.Entity;

edited Sep 03 '14 at 14:42

Ryan Kohn

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answered Dec 06 '13 at 07:26

skb

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@Ryan Kohn I have applied all the solution methods described here, but none of them not solved my problem. So, could you have a look at please described on Kendo UI : Cannot convert lambda expression to type 'string' because it is not a delegate type? Thanks in advance. – Jack Feb 05 '15 at 14:31
@H.Johnson Note that I only edited this answer. *skb* is the original author. On another note, if your problem is not identical to the one described in the question, you can consider asking a new question to the community. – Ryan Kohn Feb 05 '15 at 19:28
@RyanKohn: Thanks for reply. Here is the link of my question. Could you have a look at pls? http://stackoverflow.com/questions/28354301/convert-lambda-expression-to-json-in-mvc – Jack Feb 05 '15 at 21:25
I was missing `using System.Net; ` but this helped me to figure it out. – elcool Aug 14 '15 at 17:12

score 21 · Answer 3 · edited Nov 11 '14 at 07:58

21

My case it solved i was using

@Html.DropDownList(model => model.TypeId ...)

using

@Html.DropDownListFor(model => model.TypeId ...)

will solve it

edited Nov 11 '14 at 07:58

Rory McCrossan

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answered Nov 11 '14 at 07:27

user4238584

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score 9 · Answer 4 · edited Jun 20 '20 at 09:12

If it's not related to missing using directives stated by other users, this will also happen if there is another problem with your query.

Take a look on VS compiler error list : For example, if the "Value" variable in your query doesn't exist, you will have the "lambda to string" error, and a few errors after another one more related to the unknown/erroneous field.

In your case it could be :

objContentLine = (from q in db.qryContents
                  where q.LineID == Value
                  orderby q.RowID descending
                  select q).FirstOrDefault();

Errors:

Error 241 Cannot convert lambda expression to type 'string' because it is not a delegate type

Error 242 Delegate 'System.Func<..>' does not take 1 arguments

Error 243 The name 'Value' does not exist in the current context

Fix the "Value" variable error and the other errors will also disappear.

score 5 · Answer 5 · answered Jul 24 '14 at 14:31

For people just stumbling upon this now, I resolved an error of this type that was thrown with all the references and using statements placed properly. There's evidently some confusion with substituting in a function that returns DataTable instead of calling it on a declared DataTable. For example:

This worked for me:

DataTable dt = SomeObject.ReturnsDataTable();

List<string> ls = dt.AsEnumerable().Select(dr => dr["name"].ToString()).ToList<string>();

But this didn't:

List<string> ls = SomeObject.ReturnsDataTable().AsEnumerable().Select(dr => dr["name"].ToString()).ToList<string>();

I'm still not 100% sure why, but if anyone is frustrated by an error of this type, give this a try.

THANKS! Here's my iteration: dtSQLServers.AsEnumerable().Where(dr => dr["SourceSystem"].ToString() == "xxxxxxxxx").ToList() — ARLibertarian, Apr 22 '19 at 18:01

Cannot convert lambda expression to type 'string' because it is not a delegate type

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