LINQ : Dynamic select

Question

Consider we have this class :

    public  class Data
{
    public string Field1 { get; set; }
    public string Field2 { get; set; }
    public string Field         


        

Answer 1

The OP mentioned Dynamic Linq library, so I'd like to lay out an explanation on its usage.

1. Dynamic Linq Built-In Select

Dynamic Linq has a built-in Select method, which can be used as follows:

var numbers = new List { 1, 2, 3 };
var wrapped = numbers.Select(num => new { Value = num }).ToList();

// the "it" keyword functions as the lambda parameter,
// so essentialy it's like calling: numbers.Select(num => num)
var selectedNumbers = numbers.Select("it"); 

// the following is the equivalent of calling: wrapped.Select(num => num.Value)
var selectedValues = wrapped.Select("Value");

// the following is the equivalent of calling: numbers.Select(num => new { Value = num })
var selectedObjects = numbers.Select("new(it as Value)"); 

foreach (int num in selectedNumbers) Console.WriteLine(num);
foreach (int val in selectedValues) Console.WriteLine(val);
foreach (dynamic obj in selectedObjects) Console.WriteLine(obj.Value);

The Downside

There's somewhat a downside using the built-in Select:

Since it's an IQueryable - not IQueryable - extension method, with IQueryable as its return type, common materialization methods - like ToList or FirstOrDefault - can't be used. This is why the above example uses foreach - it's simply the only convenient way of materializing the results.

So to make things more convenient, let's support these methods.

2. Supporting Select in Dynamic Linq (to enable using ToList and alike)

To support Select, it needs to be added into the Dynamic Linq file. The simple steps for doing that are explained in this answer and in my comment on it.

After doing so, it can be used in the following way:

var numbers = new List { 1, 2, 3 };
var wrapped = numbers.Select(num => new { Value = num }).ToList();

// the following is the equivalent of calling: numbers.Select(num => num).ToList()
var selectedNumbers = numbers.Select("it").ToList(); 

// the following is the equivalent of calling: wrapped.Select(num => num.Value).ToList()
var selectedValues = wrapped.Select("Value").ToList();

// the following is the equivalent of calling: numbers.Select(num => new { Value = num }).ToList()
var selectedObjects = numbers.Select