Cannot convert lambda expression to type 'stri

问题:

In my controller i am trying to use include with EF4 to select related entities, but the lambda expression is throwing the following error,

i have the related entity defined in the Entity class like

public class CustomerSite
{
    public int CustomerSiteId { get; set; }
    public int CustomerId { get; set; }
    public virtual Customer Customer { get; set; }
}

Then in my controller i have

 var sites = context.CustomerSites.Include(c => c.Customer);

 public ViewResult List()
 {
    var sites = context.CustomerSites.Include(c => c.Customer);
    return View(sites.ToList());
 }

Can anyone kindly point me in the right direction on what i'm doing wrong here?

回答1:

The Include method expects a string, not a lambda:

public ViewResult List()
{
    var sites = context.CustomerSites.Include("Customer");
    return View(sites.ToList());
}

Of course you could write a custom extension method which would work with lambda expressions and make your code independant of some magic strings and refactor friendlier.

But whatever you do PLEASE OH PLEASE don't pass EF autogenerated objects to your views. USE VIEW MODELS.

回答2:

Well, the post is quite old, but just replying here to update it. Well, the Include() method with Entity Framework 4.1 has extension methods and it also accepts a lambda expression. So

context.CustomerSites.Include(c => c.Customer);

is perfectly valid, all you need to do is use this:

using System.Data.Entity;

回答3:

Include is an extension method in the System.Data.Entity namespace, you need to add:

using System.Data.Entity;

Then you can use the lambda expression, instead of the string.

回答4:

Include takes a string, not a lambda expression.
Change it to CustomerSites.Include("Customer")

回答5:

If you are getting this error in Razor:

Ex:

@Html.RadioButtonFor(model => model.Security, "Fixed", new { @id = "securityFixed"})                            

C# doesn't know how to convert the string to valid bool or known type.

So change your string as below:

@Html.RadioButtonFor(model => model.Security, "True", new { @id = "securityFixed"}) 

or

@Html.RadioButtonFor(model => model.Security, "False", new { @id = "securityFixed"})