Protobuf-net KeyedCollection serialization

Question

I need to serialize/deserialize a KeyedCollection with protobuf.net, can I just serialize a list?

If so, what is the most efficient way to convert-back the List to the KeyedCollection?

Here follows a sample code that shows the case:

public class FamilySurrogate
{
    public List<Person> PersonList { get; set; }

    public FamilySurrogate(List<Person> personList)
    {
        PersonList = personList;
    }


    public static implicit operator Family(FamilySurrogate surrogate)
    {
        if (surrogate == null) return null;

        var people = new PersonKeyedCollection();
        foreach (var person in surrogate.PersonList)  // Is there a most efficient way?
            people.Add(person);

        return new Family(people);

    }

    public static implicit operator FamilySurrogate(Family source)
    {
        return source == null ? null : new FamilySurrogate(source.People.ToList());
    }

}

public class Person
{
    public Person(string name, string surname)
    {
        Name = name;
        Surname = surname;
    }
    public string Name { get; set; }
    public string Surname { get; set; }
    public string Fullname { get { return $"{Name} {Surname}"; } }
}

public class PersonKeyedCollection : System.Collections.ObjectModel.KeyedCollection<string, Person>
{        
    protected override string GetKeyForItem(Person item) { return item.Fullname; }
}

public class Family
{
    public Family(PersonKeyedCollection people)
    {
        People = people;
    }

    public PersonKeyedCollection People { get; set; }
}

Answer 1

Solution?

.NET Platform Extensions 6 has an implementation of the KeyedCollection, KeyedByTypeCollection Class . This has a constructor which accepts an IEnumerable. The downside to this implementation is that the keys are the items , and it doesn't appear to allow you to change that. If you're already inheriting KeyedCollection, you may as well follow the implementation here and go by Microsoft's lead; they just iterate and call Add() .

See also

• Uses of KeyedByTypeCollection in.Net?
• Can't seem to resolve KeyedByTypeCollection?
• What are .NET Platform Extensions on learn.microsoft.com?
• Linq with custom base collection
• Collection Initializers

Previous thoughts

I'm also trying to tackle this issue from a Linq query perspective, possibly related posts:

• Cannot implicitly convert type System.Collections.Generic.List back to Object after linq query
• do.net/runtime: Why is KeyedCollection abstract?

The core issue seems to be that KeyedCollectedion does not contain a constructor that takes any form of ICollection to initialize its data with. The base class of KeyedCollection, Collection , does however. The only option seems to be writing your own constructor for your KeyedCollection class that iterates over a collection and adds each element to the current instance.

using System.Collections.Generic;
using System.Collections.ObjectModel;

public class VariableList<T> : KeyedCollection<string, T>
{
    // KeyedCollection does not seem to support explicitly casting from an IEnumerable,
    // so we're creating a constructor who's sole purpose is to build a new KeyedCollection.
    public VariableList(IEnumerable<T> items)
    {
        foreach (T item in items)
            Add(item);
    }

    // insert other code here
}

This seems really inefficient though, so I hope someone corrects me...

Edit: John Franco wrote a blogpost wherein they hack together a solution for genericly casting a List with covariants (in 2009.) This doesn't look like a very good way to do things.

Looking at System.Linq.Enumerable's implementation of ToList, Linq also iterates and Adds to the new collection.