how to map an anonymous object to a class by AutoMapper?

Question

I have an entity:

public class Tag {
    public int Id { get; set; }
    public string Word { get; set; }
    // other properties...
    // and a collection of blogposts:
    public ICollection<Post> Posts { get; set; }
}

and a model:

public class TagModel {
    public int Id { get; set; }
    public string Word { get; set; }
    // other properties...
    // and a collection of blogposts:
    public int PostsCount { get; set; }
}

and I query the entity like this (by EF or NH ):

var tagsAnon = _context.Tags
    .Select(t => new { Tag = t, PostsCount = t. Posts.Count() })
    .ToList();

Now, how can I map the tagsAnon (as an anonymous object ) to a collection of TagModel (eg ICollection<TagModel> or IEnumerable<TagModel> )? Is it possible?

Answer 1

Update 2019-07-31 : CreateMissingTypeMaps is now deprecated in AutoMapper v8, and will be removed in v9 .

Support for automatically created maps will be removed in version 9.0. You will need to explicitly configure maps, manually or using reflection. Also consider attribute mapping .

---

Update 2016-05-11 : DynamicMap is now obsolete .

Now you need to create a mapper from a configuration that sets CreateMissingTypeMaps to true :

var tagsAnon = Tags
    .Select(t => new { t.Id, t.Word, PostsCount = t.Posts.Count })
    .ToList();

var config = new MapperConfiguration(cfg => cfg.CreateMissingTypeMaps = true);
var mapper = config.CreateMapper();

var tagsModel = tagsAnon.Select(mapper.Map<TagModel>)
    .ToList();

---

Yes, it is possible. You would have to use the DynamicMap<T> method of the Automapper's Mapper class for each anonymous object you have. Something like this:

var tagsAnon = Tags
    .Select(t => new { t.Id, t.Word, PostsCount = t.Posts.Count() })
    .ToList();

var tagsModel = tagsAnon.Select(Mapper.DynamicMap<TagModel>)
    .ToList();

Answer 2

I am not entirely sure if this is possible. Suggestions:

Why can't you just do this:

var tagsAnon = _context.Tags
    .Select(t => new TagModel { Tag = t, PostsCount = t. Posts.Count() })
    .ToList();

This SHOULD work, however it fails (I have read that DynamicMap is iffy on collections.

var destination = Mapper.DynamicMap<IEnumerable<TagModel>>(tagsAnon);

This proves that DynamicMap does work with anon types, just not seemingly with enumerables:

var destination = Mapper.DynamicMap<TagModel>(tagsAnon);

Answer 3

You can create a custom function to achieve this with latest Automapper. It uses the CreateMissingTypeMaps property as mentioned in other answers above.

public static List<T> MapDynamicList<T>(IEnumerable<object> obj)
    {
        var config = new MapperConfiguration(c => c.CreateMissingTypeMaps = true);
        var mapper = config.CreateMapper();

        var newModel = obj.Select(mapper.Map<T>).ToList();

        return newModel;
    }

Then you just call the function with this single line of code:

var viewModel = Models.Helper.MapDynamicList<MatchSubCategory>(model);

where model is the IEnumerable<object> or List<object> .

Answer 4

Since all anonymous types derived from System.Object, I found a solution (workaround) to add mapping from object to your destination type

            //Allow to map anonymous types to concrete type
            cfg.CreateMap(typeof(object), typeof(ExternalCandle), 
                MemberList.None);

But please note that for most scenarios this is not the correct solution For example, if you want to map ORM types - go with this way: Queryable Extensions

I guess that Jimmy bogard won't recommend this solution because of the same reason that CreateMissingTypeMaps was removed from AutoMappers's API -https://github.com/AutoMapper/AutoMapper/issues/3063

So maybe in a future version of AutoMapper this code won't work (I am using AutoMapper 10.1.1 and it worked for me)