system.linq.IQueryable 不包含“To”的定义

Question

I get an error in this code:

this is the code:

  public IHttpActionResult  Get()
    {
        var books = unit.Books.All;

        var response = books.To<BookDto>();

        return Ok(response);
    }

and right on books.To() I am getting this error:

system.linq.IQueryable does not contain a definition for 'To' and
extension method 'to' accepting a first argument of type 'system.linq.IQueryable' could be found. you you missing a using directive or an assembly reference?

I looked at this but no help.

IQueryable<T> does not contain a definition for 'Include' and no extension method 'Include'

I have using System.Data.Entity; and also I have installed the EF from NuGet , but as the solution in the link I cant get the "QueryableExtensions" available in

 using System.Data.Entity.QueryableExtensions

Answer 1

QueryableExtensions doesn't appear to contain any function named To , nor have I have ever heard of this method, so I suspect you're barking up the wrong tree in that regard.

You likely need one of the following:

1. var response = books.ToList(); for a List of books

2. var response = books.Cast<BookDto>(); to cast each objects in books to BookDto

3. var response = books.Select(book => new BookDto(book)); to construct a sequence of BookDto objects from books , assuming there is a suitable constructor.

Answer 2

IQueryable.To<T> isn't a thing. If you're trying to convert to a different type, you'll likely need to use Select , eg.

var response = books.Select(book => new BookDto()); //Insert transformation logic into the new object initialization.

If you're trying to make a list, then simply do this:

var response = books.ToList();