converting entities to viewmodels for use with web api

Question

I'm currently struggling with finding a better way to populate my ViewModel objects with my Entitiy objects. I have the following Web Api controller method:

[HttpGet]
public IEnumerable<ClientSearchViewModel> FindClients(string query)
{
    var clients = _clientService.SearchClient(query).ToList();
    var returnClients = new List<ClientSearchViewModel>();
    foreach (var client in clients)
    {
        returnClients.Add(new ClientSearchViewModel(client));
    }
    return returnClients;
}

And I'm doing this in my ClientSearchViewModel constructor:

public ClientSearchViewModel(Client client)
{
    this.Id = client.Id;
    this.FirstName = client.PersonName.FirstName;
    this.LastName = client.PersonName.LastName;
}

Is there another way other than going through the list of returned objects and creating a new ViewModel list?

score 1 · Accepted Answer · edited May 23 '17 at 12:15

I strongly suggest use of a mapping plugin for this, such as:

AutoMapper

or

ValueInjector

Plugins like this will allow you to map between the objects being used internally or in your data layer, with your external objects (DTOs/ViewModels). They handle a number of things out of the box such as automatic mapping of any like named properties with the same type, but also allow for a lot of control in the specific mapping of properties or types, for those times when you need something more custom.

For a brief comparison of the two, there isn't much better than hearing the authors themselves respond: AutoMapper vs ValueInjecter

Personally, I find ValueInjector to be quicker to use, while having more control overall, but I also find it to be much less readable/inuitive than AutoMapper, which can require a bit more code to accomplish similar goals. As such, I'd pick the one that you find you and/or your team will prefer the syntax of and how easily you can grasp the concepts vs how much power you really need.

Any personal preference of one over the other? or some quick Pros and Cons for both? — SOfanatic, Aug 08 '13 at 15:16
Added a link with some more information from the actual authors. — Sethcran, Aug 08 '13 at 15:22

score 1 · Answer 2 · answered Aug 08 '13 at 15:21

So I had the same miff... I can't say that I've benchmarked my solution, but it does seem to run reasonably fast...

3 bits:

public static T Transform<T>(this object convertFrom) where T : class, new()
        {
            return (T) (new ServiceExtension().Transform(convertFrom, typeof (T)));

        }

private class ServiceExtension
        {
            public object Transform(object convertFrom, Type convertTo)
            {
                object _t = Activator.CreateInstance(convertTo);
                if (convertFrom == null) return _t;

                var convertType = convertFrom.GetType();
            foreach (
                var property in _t.GetType().GetProperties().Where(f => f.CanWrite && f.GetSetMethod(true).IsPublic)
                )
            {
                if (property.GetCustomAttributes(typeof (TransformAttribute), true).Any())
                {
                    var transform =
                        (property.GetCustomAttributes(typeof (TransformAttribute), true).FirstOrDefault() as
                         TransformAttribute);
                    var transformname = transform.RelatedField ?? property.Name;

                    if (convertType.GetProperty(transformname) == null)
                        throw new ArgumentException(
                            string.Format(
                                "We were unable to find property:\"{0}\" on {1}.  Please check the RelativeField value on the {2} for \"{0}\"",
                                transformname, convertFrom.GetType().Name, convertTo.Name));

                    var theValue = convertType.GetProperty(transformname).GetValue(convertFrom);

                    if (isCollection(theValue))
                    {
                        foreach (var item in (theValue as ICollection))
                        {
                            var someVal = new object();
                            var newToType = property.PropertyType.GetGenericArguments().FirstOrDefault();

                            if (!String.IsNullOrEmpty(transform.FullyQualifiedName))
                                someVal =
                                    Transform(
                                        item.GetType().GetProperty(transform.FullyQualifiedName).GetValue(item),
                                        newToType);

                            else
                                someVal = Transform(item, newToType);
                            if (property.GetValue(_t) == null)
                                throw new NullReferenceException(
                                    string.Format(
                                        "The following property:{0} is null on {1}.  Likely this needs to be initialized inside of {1}'s empty constructor",
                                        property.Name, _t.GetType().Name));
                            property.PropertyType.GetMethod("Add")
                                    .Invoke(property.GetValue(_t), new[] {someVal});
                            //property.SetValue(_t, theValue.Transform(theValue.GetType()));
                        }
                    }
                    else
                        property.SetValue(_t, theValue);
                }
                //property.SetValue(_t, property.GetValue(convertFrom, null), null);
            }

            return _t;
        }

        public bool isCollection(object o)
        {
            return o is ICollection
                   || typeof (ICollection<>).IsInstanceOfType(o);
        }
    }


public class TransformAttribute : Attribute
    {
        public string RelatedField { get; private set; }
        public string FullyQualifiedName { get; set; }

    public TransformAttribute()
    {
    }

    public TransformAttribute(string relatedField)
    {
        RelatedField = relatedField;
    }

}

such that the end result is: myObject.Transform()

But the decorations let you account for differences between your POCO and your ViewModel

converting entities to viewmodels for use with web api

2 Answers2