Automatic update existing Class properties from an instance of the same class

Question

Recently I came up with an idea (that I really don't know whether it would exist or even work) of automatically updating a Class's properties using a modified instance of it. And, to make my idea a little bit more clear, I will explain it in the code below"

//The first (Main) instance of the Class
Employee carl = new Employee();
carl.Name = "Carl";
carl.Age = 20;
carl.Salary = 7000;

//Here is the same employee data collected from the database a year after:

Employee carl_one_year_later = new Employee();
carl_one_year_later.Age = 21;
carl_one_year_later.Salary = 10000;

//My idea is that I want to dynamically merge the new collected data to the current main instance of the employee, without missing out the unupdated data (i.e.: his name)
employee1 = employee2; //Using this seems to overwrite the Name Field with Null.

Some might say you can simply achieve this by doing this:

carl.Age = carl_one_year_later.Age;
carl.Salary = carl_one_year_later.Salary;

However, I want a dynamic way to just do this in 1 line of code and let C# handle the property set for me. Also, it may come in handy if we have a massive class that we don't want to set its properties every time they are updated one by one.

how about using reflection to iterate over properties and set those except which are null or default? — gp., Oct 16 '13 at 03:07
@gp.: Sorry i don't have experience with reflection, and if it really does what i am talking about, and in 1 line or (the less as possible). You may provide me with an detailed answer about how i could achieve it. — Daniel Eugen, Oct 16 '13 at 03:09
Also, don't forget to take into account that as you say, i only want to get from the updated class the values that are not (null, or default) and set those value to the default main class... — Daniel Eugen, Oct 16 '13 at 03:11
We used to have this in COBOL, and I sometimes wish we still did. It was called [MOVE CORRESPONDING](http://stackoverflow.com/questions/719135/whats-the-bright-side-of-cobol/719176#719176). — John Saunders, Oct 16 '13 at 04:19

score 2 · Accepted Answer · edited Oct 18 '13 at 00:01

using System;
using System.Reflection;

public class Test
{
    public class Employee
    {
        public String Name{get;set;}
        public int Age{get;set;}
        public int Salary{get;set;}
    }
    public static void Main()
    {
        Employee e1 = new Employee{Name="Old", Age=20, Salary=1000};
        Employee e2 = new Employee{Age=30, Salary=5000};

        Copy(e2, e1);

        Console.WriteLine(e1.Name+" "+ e1.Age+" "+e1.Salary );
    }

    public static void Copy<T>(T from, T to)
    {
        Type t = typeof (T);
        PropertyInfo[] props = t.GetProperties(BindingFlags.Public | BindingFlags.Instance);
        foreach (PropertyInfo p in props) {
            if (!p.CanRead || !p.CanWrite) continue;

            object val = p.GetGetMethod().Invoke(from, null);
            object defaultVal = p.PropertyType.IsValueType ? Activator.CreateInstance(p.PropertyType) : null;
            if (null != defaultVal && !val.Equals(defaultVal)) {
                p.GetSetMethod().Invoke(to, new[] {val});
            }
        }
    }
}

can you tell me what are the drawbacks you expect from the above code ? — Daniel Eugen, Oct 16 '13 at 10:16

rossipedia · Answer 2 · 2021-08-05T18:27:31.463

1

You can make a CopyTo extension method, like so:

public static class ObjectExtensions
{
    public static void CopyTo<T>(this T fromObj, T toObj)
    {
        foreach(var p in typeof(T).GetProperties()) 
        {
            p.SetValue(toObj, p.GetValue(fromObj, null), null);
        }
    }
}

And call it like:

carl_one_year_later.CopyTo(carl);

Although, to be honest, there's a few more checks that should be made, and you'd be better off using something like AutoMapper instead.

edited Aug 05 '21 at 18:27

answered Oct 16 '13 at 03:34

rossipedia

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1

It looks as though you intended to name your extension method `CopyTo` rather than `CopyProperties`. – M.Babcock Oct 16 '13 at 03:41

score 0 · Answer 3 · edited May 23 '17 at 12:21

Checkout ICloneable OR MemberwiseClone (unless you need to do a deep copy. Then check out a object mapper like Automapper, ValueInjecter or write your own custom object serialization hydrater)

http://msdn.microsoft.com/en-us/library/system.object.memberwiseclone.aspx

The MemberwiseClone method creates a shallow copy by creating a new object, and then copying the nonstatic fields of the current object to the new object.

http://msdn.microsoft.com/en-us/library/system.icloneable.aspx

Alternatives to AutoMapper

score 0 · Answer 4 · answered Dec 12 '21 at 18:37

public static class ObjectExtensions
    {
        public static void CopyTo<T>(this T fromObj, T toObj)
        {
            foreach (var p in typeof(T).GetProperties())
            {
                if(p.GetValue(fromObj) == null)
                {
                    continue;
                }
                p.SetValue(toObj, p.GetValue(fromObj, null), null);
            }
        }
    }

Same as the above answer but just added "if" in "foreach" to skip the null values

score -1 · Answer 5 · answered Oct 16 '13 at 05:09

The idea itself seems odd to me..

I, myself, would just rather do :

//The first (Main) instance of the class
Employee carl = new Employee();
carl.Name = "Carl";
carl.Age = 20;
carl.Salary = 7000;

//Here we get Carl from the database
Employee carl = GetFromDatabase("Carl") //Illustration
carl.Age = 21;
carl.Salary = 10000;

Your code is like saying nowadays Carl and next year Carl is a completely different person, and coincidentally having all those same attributes.

Although if it really needs to be done, I do tend to prefer Automapper..

Automatic update existing Class properties from an instance of the same class

5 Answers5