使用密鑰將列表映射到Automapper中的現有列表

Question

Automapper可以輕松處理將一個對象類型列表映射到另一個不同對象類型的列表，但是是否可以使用ID作為鍵將其映射到現有列表？

Answer 1

我沒有找到比以下更好的方法。

這是源和目的地。

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; }
}

定義轉換器（您應該將List <>更改為您正在使用的任何類型）。

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;
    }
}

這是實際的映射配置和示例。

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);

您應該得到以下結果。

Answer 2

我發現這篇文章非常有用，因此我認為我會反饋我的通用版本的類型轉換器，您可以使用它來從每個對象中選擇要匹配的屬性。

使用它你需要做的就是：

// 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;
    }
}