using System;

using System.Collections.Generic;

using System.ComponentModel.DataAnnotations;

using System.Linq;

​

public class SomethingNested

{

    [Required]

    public string SomeString { get; set; }

​

    [Required]

    public int SomeNumber { get; set; }

​

    public bool SomeBoolean { get; set; }

​

    public List<string> SomeStringList { get; set; }

​

}

​

public class MyWidget

{

    [Required]

    public SomethingNested SomethingNested { get; set; }

​

    public string SomeString { get; set; }

​

    public int SomeNumber { get; set; }

​

    public bool SomeBoolean { get; set; }

​

    [Required]

    public List<string> SomeStringList { get; set; }

}

​

public class Program

{

    public static void Main()

    {

        var myWidget = new MyWidget

        {

            SomethingNested = new SomethingNested

            {

                SomeString = null,

                SomeNumber = 123,

                SomeBoolean = true,

                SomeStringList = new List<string> { "a", "b", null }

            },

            SomeString = null,

            SomeNumber = 123,

            SomeBoolean = true,

            SomeStringList = null

        };

​

        // Only run for required properties of myWidget

        // AssertPropertiesAreNonNull(myWidget);

        // Run for ALL properties in myWidget

        AssertPropertiesAreNonNull(myWidget, false);

    }

    // Asserts that all required properties (via the 'Required' attribute) be non null

    // Optionally include all properties if desired

    private static void AssertPropertiesAreNonNull<T>(T obj, bool onlyRequiredProperties = true)

    {

        if (obj == null)

        {

            return;

        }

​

        var objType = obj.GetType();

​

        // Get either all or only required properties

        var properties = onlyRequiredProperties ? objType.GetProperties()

            .Where(x => x.GetCustomAttributes(false).OfType<RequiredAttribute>().Any()) : 

        objType.GetProperties();

​

        foreach (var property in properties)

        {

            var propValue = property.GetValue(obj, null);

            var elems = propValue as IList<object>;

​

            // Another layer 

            if (elems != null)

            {

                foreach (var item in elems)

                {

                    AssertPropertiesAreNonNull(item, onlyRequiredProperties);

                }

            }

            else

            {

                if (property.PropertyType.Assembly == objType.Assembly)

                {

                    AssertPropertiesAreNonNull(propValue, onlyRequiredProperties);

                }

                // Reached the end of the tree

                else

                {

                    Console.WriteLine($"Evaluating {property.Name}...");

                    // Prepare error message

                    var errorMessage = $"Property '{property.Name}' is null!";

                    // Various options for what you want to do if a property is null. 

                    // Toggle with comments or delete to your liking:

                    // Simply log it out:

                    if (propValue == null) 

                    {

                        Console.WriteLine(errorMessage);

                    }

​

                    // If using Shouldly:

                    //propValue.ShouldNotBeNull();

​

                    // Or simply the angry way - throw an exception!

                    //if (propValue == null)

                    //{

                    //  throw new Exception(errorMessage);

                    //}

                }

            }

        }

    }

}