Geek asks and answers

List maps into an existing list in Automapper using a key

Automapper easily handles the mapping of one list of object types to another list of different types of objects, but is it possible to map it to an existing list using an identifier as a key?

+5
source share
2 answers

I have not found a better way than the following.

Here is the source and destination.

public class Source
{
    public int Id { get; set; } 
    public string Foo { get; set; }
}

public class Destination 
{ 
    public int Id { get; set; }
    public string Foo { get; set; }
}

Define a converter (you must change List <> to whatever type you use).

public class CollectionConverter: ITypeConverter<List<Source>, List<Destination>>
{
    public List<Destination> Convert(ResolutionContext context)
    {
        var destinationCollection = (List<Destination>)context.DestinationValue;
        if(destinationCollection == null)
            destinationCollection = new List<Destination>();
        var sourceCollection = (List<Source>)context.SourceValue;
        foreach(var source in sourceCollection)
        {
            Destination matchedDestination = null;

            foreach(var destination in destinationCollection)
            {
                if(destination.Id == source.Id)
                {
                    Mapper.Map(source, destination);
                    matchedDestination = destination;
                    break;
                }
            }
            if(matchedDestination == null)
                destinationCollection.Add(Mapper.Map<Destination>(source));
        }
        return destinationCollection;
    }
}

And here is the actual display configuration and example.

Mapper.CreateMap<Source,Destination>();
Mapper.CreateMap<List<Source>,List<Destination>>().ConvertUsing(new CollectionConverter());

var sourceCollection = new List<Source>
{
    new Source{ Id = 1, Foo = "Match"},
    new Source{ Id = 2, Foo = "DoesNotMatchWithDestination"}
};
var destinationCollection = new List<Destination>
{
    new Destination{ Id = 1, Foo = "Match"},
    new Destination{ Id = 3, Foo = "DoeNotMatchWithSource"}
};
var mergedCollection = Mapper.Map(sourceCollection, destinationCollection);

You should get the following result.

Mapping result

+7
source

, , , , .

, , :

// Example of usage
Mapper.CreateMap<UserModel, User>();
var converter = CollectionConverterWithIdentityMatching<UserModel, User>.Instance(model => model.Id, user => user.Id);
Mapper.CreateMap<List<UserModel>, List<User>>().ConvertUsing(converter);

//The actual converter
public class CollectionConverterWithIdentityMatching<TSource, TDestination> : 
    ITypeConverter<List<TSource>, List<TDestination>> where TDestination : class
{
    private readonly Func<TSource, object> sourcePrimaryKeyExpression;
    private readonly Func<TDestination, object> destinationPrimaryKeyExpression;

    private CollectionConverterWithIdentityMatching(Expression<Func<TSource, object>> sourcePrimaryKey, Expression<Func<TDestination, object>> destinationPrimaryKey)
    {
        this.sourcePrimaryKeyExpression = sourcePrimaryKey.Compile();
        this.destinationPrimaryKeyExpression = destinationPrimaryKey.Compile();
    }

    public static CollectionConverterWithIdentityMatching<TSource, TDestination> 
        Instance(Expression<Func<TSource, object>> sourcePrimaryKey, Expression<Func<TDestination, object>> destinationPrimaryKey)
    {
        return new CollectionConverterWithIdentityMatching<TSource, TDestination>(
            sourcePrimaryKey, destinationPrimaryKey);
    }

    public List<TDestination> Convert(ResolutionContext context)
    {
        var destinationCollection = (List<TDestination>)context.DestinationValue ?? new List<TDestination>();
        var sourceCollection = (List<TSource>)context.SourceValue;
        foreach (var source in sourceCollection)
        {
            TDestination matchedDestination = default(TDestination);

            foreach (var destination in destinationCollection)
            {
                var sourcePrimaryKey = GetPrimaryKey(source, this.sourcePrimaryKeyExpression);
                var destinationPrimaryKey = GetPrimaryKey(destination, this.destinationPrimaryKeyExpression);

                if (string.Equals(sourcePrimaryKey, destinationPrimaryKey, StringComparison.OrdinalIgnoreCase))
                {
                    Mapper.Map(source, destination);
                    matchedDestination = destination;
                    break;
                }
            }

            if (matchedDestination == null)
            {
                destinationCollection.Add(Mapper.Map<TDestination>(source));
            }
        }

        return destinationCollection;
    }

    private string GetPrimaryKey<TObject>(object entity, Func<TObject, object> expression)
    {
        var tempId = expression.Invoke((TObject)entity);
        var id = System.Convert.ToString(tempId);
        return id;
    }
}
+1

More articles:


All Articles