c# - 使用 AutoMapper 自定义映射

Question

我有两个非常简单的对象:

public class CategoryDto
{
    public string Id { get; set; }

    public string MyValueProperty { get; set; }
}

public class Category
{
    public string Id { get; set; }

    [MapTo("MyValueProperty")]
    public string Key { get; set; }
}

当使用 AutoMapper 将 Category 映射到 CategoryDto 时，我想要以下行为:

除了具有 MapTo 属性的属性外，属性应该照常映射。在这种情况下，我必须读取 Attribute 的值才能找到目标属性。源属性的值用于查找要注入(inject)目标属性的值(借助字典)。一个例子总比 1000 个单词好...

例子:

Dictionary<string, string> keys = 
    new Dictionary<string, string> { { "MyKey", "MyValue" } };

Category category = new Category();
category.Id = "3";
category.Key = "MyKey";

CategoryDto result = Map<Category, CategoryDto>(category);
result.Id               // Expected : "3"
result.MyValueProperty  // Expected : "MyValue"

Key 属性映射到 MyValueProperty(通过 MapTo 属性)，分配的值为“MyValue”，因为源属性值是映射(通过字典)到“MyValue”的“MyKey”。

这可以使用 AutoMapper 吗？我当然需要一个适用于每个对象的解决方案，而不仅仅是适用于 Category/CategoryDto。

Answer 1

我终于(经过这么多小时!!!!)找到了解决方案。我与社区分享这个；希望它能帮助别人......

编辑:请注意，它现在更简单了(AutoMapper 5.0+)，您可以按照我在这篇文章中的回答进行操作:How to make AutoMapper truncate strings according to MaxLength attribute?

public static class Extensions
{
    public static IMappingExpression<TSource, TDestination> MapTo<TSource, TDestination>(this IMappingExpression<TSource, TDestination> expression)
    {
        Type sourceType = typeof(TSource);
        Type destinationType = typeof(TDestination);

        TypeMap existingMaps = Mapper.GetAllTypeMaps().First(b => b.SourceType == sourceType && b.DestinationType == destinationType);
        string[] missingMappings = existingMaps.GetUnmappedPropertyNames();

        if (missingMappings.Any())
        {
            PropertyInfo[] sourceProperties = sourceType.GetProperties();
            foreach (string property in missingMappings)
            {
                foreach (PropertyInfo propertyInfo in sourceProperties)
                {
                    MapToAttribute attr = propertyInfo.GetCustomAttribute<MapToAttribute>();
                    if (attr != null && attr.Name == property)
                    {
                        expression.ForMember(property, opt => opt.ResolveUsing(new MyValueResolve(propertyInfo)));
                    }
                }
            }
        }

        return expression;
    }
}

public class MyValueResolve : IValueResolver
{
    private readonly PropertyInfo pInfo = null;

    public MyValueResolve(PropertyInfo pInfo)
    {
        this.pInfo = pInfo;
    }

    public ResolutionResult Resolve(ResolutionResult source)
    {
        string key = pInfo.GetValue(source.Value) as string;
        string value = dictonary[key];
        return source.New(value);
    }
}