Return current item, in lamba method of Select.

Question

Hello,

i have an external list of items homogeneous with my entities,
i have to update the entities setting a flag to true,

After many attempts this is my code :

 var insideItems= outsideItems.ToList().Select(x => { x.IsNew = true; return x; });

the code working fine, the outsideItems is a IQueryAble list of my entities, but my question is, why i need to have a "return x" in code and i cannot do:

 var insideItems= outsideItems.ToList().Select(x => { x.IsNew = true; });

just setting the flag, due the error : "The type arguments for method 'Enumerable.Select<TSource, TResult>(IEnumerable<TSource>, Func<TSource, int, TResult>)' cannot be inferred from the usage. Try specifying the type arguments explicitly."

Sorry for newby question but i would to understand better.

Answer 1

Select expects a return of type T (your concrete class). In the following. We don't need to be concerned with IQueryable aspect, just a the .List -> Select.

Using

namespace Example1.Classes  
{  
    public class Person  
    {  
        public string FirstName { get; set; }  
        public string LastName { get; set; }  
        public int Id { get; set; }  
        public bool Active { get; set; }  
        public bool IsNew { get; set; }  
    }  
}  

We can change a property value, in this case all person objects in the list.

Change IsNew

using System;  
using System.Collections.Generic;  
using System.Linq;  
using Example1.Classes;  
  
namespace Example1  
{  
    public class Operations  
    {  
        public Operations()  
        {  
            List<Person> list = GetPeopleList();  
            list.ForEach(person => person.IsNew = true);  
        }  
        public List<Person> GetPeopleList()  
        {  
  
            return new List<Person>  
            {  
                new Person()  
                {  
                    Id = 1,  
                    FirstName = "Pete",  
                    LastName = "Smith",  
                    Active = true,   
                    IsNew = false  
                },  
                new Person()  
                {  
                    Id = 2,  
                    FirstName = "Karen",  
                    LastName = "Payne",  
                    Active = true,  
                    IsNew = false  
                },  
                new Person()  
                {  
                    Id = 3,  
                    FirstName = "Jane",  
                    LastName = "Williams",  
                    Active = true,  
                    IsNew = false  
                }  
            };  
        }  
  
  
    }  
}