C# - How to use Select LINQ method using properties from a dynamically list of properties

Question

Suppose we have a simple class called Person with properties as FirstName, LastName, Age .

Now I have a list of properties as a list of strings.

var props = new List<string> { "FirstName", "Age"}.

Now I have a List of Person objects.

var persons = new List<Person> {....}

How to use Select LINQ method to get just the Person properties that appear in the props ?

var result = persons.Select(p => code here)

The result should be a list of anonymous objects, where an anonymous object should contain the properties from props list.

Answer 1

Could you try this:

IEnumerable<string> personProps = typeof(Person).GetProperties().Select(p => p.Name);

List<string> props = new List<string> { "FirstName", "Age"};

IEnumerable<string> selectedProps = props.Where(p => personProps.Contains(p));

Answer 2

If I get your question correctly you want to kind of trim your Person object. If that's correct I'd recommend to create an instance method inside your Person class that gives you the opportunity to create an unnamed object or Tuple (for example like here: C# ValueTuple of any size ) directly from your Person instanciated object. You just need to pass your props List for matching the properties (like here: enter link description here ) then and just use this very method inside your Select statement.

Answer 3

try this code. It was tested in Visual Studio and works properly

var props = new List<string> { "FirstName", "Age" };

var persons = new List<Person> { 
                  new Person { FirstName = "FirstName1", LastName = "FirstName1", Age=10},
                  new Person { FirstName = "FirstName2", LastName = "FirstName2", Age=20},
                  new Person { FirstName = "FirstName3", LastName = "FirstName3", Age=30}
    
    };

    var json = Newtonsoft.Json.JsonConvert.SerializeObject(persons);
    var jArray = JArray.Parse(json);

    List<JObject> list = new List<JObject>();

    foreach (var item in jArray)
    {
        JObject jsonObj = new JObject();
        foreach (var prop in props)
        {
            foreach (JProperty jprop in item)
            {
                if (jprop.Name == prop)
                    jsonObj.Add(jprop);
            }
        }

        list.Add(jsonObj);
    }

json = JsonConvert.SerializeObject(jsonList);

to use it you can convert to dictionary for example

var dictArray = JsonConvert.DeserializeObject<Dictionary<string, object>[]>(json);

or list of tuples or key-value pairs

List<(string,object)> values = dictArray.SelectMany(i=>i).Select(i =>(i.Key,i.Value)).ToList();

output

    FirstName   FirstName1
    Age         10
    FirstName   FirstName2
    Age         20
    FirstName   FirstName3
    Age         30

or you can convert to dynamic object

dynamic eo = dictArray.Select( e=> e.Aggregate(new ExpandoObject() as IDictionary<string, Object>,
                                (a, p) => { a.Add(p.Key, p.Value); return a; })).ToList();

test

var firstName = eo[1].FirstName; //FirstName2

class

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }
}