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

Solution 1

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

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

Solution 2

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

Solution 3

My case it solved i was using

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

using

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

will solve it

Solution 4

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.

Solution 5

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.

View more solutions

Comments

[Ortund]

Thank you! That sorted me out :)

[ThomasSquall]

It has worked for me :)

[Laurence]

got the same problem and your answer helped me fix it. Thanks.

[Hamad]

Why have you posted this as answer! when a different answer is accepted as correct answer?

[Jack]

@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.

[Ryan Kohn]

@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.

[Jack]

@RyanKohn: Thanks for reply. Here is the link of my question. Could you have a look at pls? stackoverflow.com/questions/28354301/…

[BruceHill]

@Hamad It is perfectly fine for people to post answers to questions that already have accepted answers. This answer does give another situation where the exception reported by the OP could occur and therefore could help someone else that is getting this exception.

[elcool]

I was missing using System.Net; but this helped me to figure it out.

[Ashok kumar]

Excellent fix. Thank you for your information.

[Liquid Core]

This has to be the stupidest thing ever. Giving you a totally misleading error message instead of clearly stating that you miss a reference. Someone cannot program at microsoft. Well, thanks for the fix

[Alan Waage]

thanks, this fixed my circumstance

[gvd]

Works for me, too. Visual Studio not detect this missing using.

[Jawand Singh]

System.Data.Entity; this helped me, i was using Include() for eager loading. Thanks :)

[Umpa]

This fixed my problem! thanks.

[Yusril Maulidan Raji]

using System.Linq; fixed my issue. Thanks!

[ShrapNull]

Thank you, much appreciated, this really helped me

[James Heffer]

calm down @Hamad...

[ARLibertarian]

THANKS! Here's my iteration: dtSQLServers.AsEnumerable().Where(dr => dr["SourceSystem"].ToString() == "xxxxxxxxx").ToList()

[Pharcyde]

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.

[chindirala sampath kumar]

Took so much time to fix this simple issue. Definitely misleading error message. Adding using System.Linq fixed the issue.