Comparing two objects and copying conditionally

Question

I have the following classes:

public class Pessoal
{
    public int ID { get; set; }
    public string CPF { get; set; }
    public string PIS { get; set; }
    public string NOME { get; set; }
    ...
    ...
    ... 
}


public class Dominio : DominioBase
{

    public Pessoal Pessoal { get; set; }

    public Pessoal PessoalAlteracao { get; set; }

}   

I would like to copy the attributes of PessoalAlteracao with the values of Pessoal, but only how much value of the PessoalAlteracao is equal to null.

I can do through a if:

PessoalAlteracao.CPF = PessoalAlteracao.CPF == null ? Pessoal.CPF : PessoalAlteracao.CPF;

But I would like to use a simpler form, I would like to create a loop, by attributes and match testing values?

Answer 1

The simplest way is this:

PessoalAlteracao.CPF = PessoalAlteracao.CPF ?? Pessoal.CPF;

I put in the Github for future reference.

All other options are more complicated. Some may have fewer lines (for few properties it is not), but become more complex to do, may have difficulties in certain scenarios (it only works if clone everything at the same criteria, which may not be true today, or it may not be tomorrow) and the performance suffers.

Note that the adopted criterion does not work for types by value, and must have several. Unless you use an overridable type for this, which would pollute the object with something unnecessary just to suit a mechanism that allows the programmer to type fewer lines. Either it goes wrong or the concept is wrong and will charge one day for it.

I would not use C# reflection until absolutely necessary. When you start abusing this feature it’s because C# is the wrong language for this project.

Almost every reflection used in C# is unnecessary.

It’s obvious that if the object is usually cloned like this it makes sense to put it in a method and not keep creating code to clone everywhere you use it.

I didn’t even ask if you need to make this filter null or not. It might not need to, then it would be enough to clone in a standard way, even if it would use reflection as well, but it would not need to write its own code.

Answer 2

It is possible to do using reflection (Reflection).

Keep in mind that although this greatly shortens the code, it may have a slower execution than simply writing "in hand" property by property or using any other approach.

Depending on how the classes are going and the general rule for this value substitution, a clone would be a slightly better choice - even if it is still made use of reflection. But it is not possible to say anything without knowing the scenario better.

var pessoal = dominio.Pessoal;
var alteracao = dominio.PessoalAlteracao;

foreach(var prop in alteracao.GetType().GetProperties()) 
{
    if(prop.GetValue(alteracao, null) == null)
    {
        var novoValor = alteracao.GetType().GetProperties().First(p => p.Name == prop.Name)
                                 .GetValue(pessoal, null);
        prop.SetValue(alteracao, novoValor);
    }           
}

Full example

using System;
using System.Linq;

public class Program
{
    static Dominio _dominio = new Dominio
    {
        Pessoal = new Pessoal
        {
            ID = 1,
            CPF = "033",
            PIS = "123",
            NOME = "João"
        },

        PessoalAlteracao = new Pessoal
        {
            ID = 1,
            PIS = "987"
        }
    };

    public static void Main()
    {
        var pessoal = _dominio.Pessoal;
        var alteracao = _dominio.PessoalAlteracao;

        foreach(var prop in alteracao.GetType().GetProperties()) 
        {
            if(prop.GetValue(alteracao, null) == null)
            {
                var novoValor = alteracao.GetType().GetProperties()
                                .First(p => p.Name == prop.Name).GetValue(pessoal, null);
                prop.SetValue(alteracao, novoValor);
            }           
        }

        foreach(var prop in alteracao.GetType().GetProperties()) 
        {
           Console.WriteLine("{0}={1}", prop.Name, prop.GetValue(alteracao, null));
        }

    }
}

public class Pessoal
{
    public int ID { get; set; }
    public string CPF { get; set; }
    public string PIS { get; set; }
    public string NOME { get; set; }
}

public class Dominio
{
    public Pessoal Pessoal { get; set; }
    public Pessoal PessoalAlteracao { get; set; }

}

^{See working on . NET Fiddle}