Question

某些背景：这仅仅是我第一次玩"Password confirmation"对象，并试图简化我可能在我们的一个应用程序中使用的对象。我从事C＃开发人员已超过10年，但直到现在再也没有理由跳进表达式中。

我正在尝试生成扩展方法来修改表达式的返回值。更具体地说，我正在尝试添加在创建AutoMapper映射时要使用的扩展方法。

示例地图：

Expression

我想做的就是创建一个扩展方法，这样我就不必在各处map.CreateMap<Widget, WidgetModel>() .ForMember(x => x.Count, opts => opts.MapFrom(src => src.Count + 1));进行编写，而只需将其写为：

+ 1

让map.CreateMap<Widget, WidgetModel>() .Increment(x => x.Count, src => src.Count);为我做Increment()。

我四处张望，以至于意识到+ 1可能是我所需要的，但是我不确定从那里去哪里？

这个the documentation看起来很相似，但是我无法将其转换为我的用例。

Answer 1

您可以使用Expression.Increment而不是+ 1。或者我们可以使其真正通用。

类似这样的东西：

void Main()
{
    var mapperConfiguraiton = 
        new MapperConfiguration(cfg => 
            cfg.CreateMap<Widget, WidgetModel>()
               .Increment(x => x.CountD, src => src.Count)
               .ToUpper(x => x.Name, src=>src.Name));

    var widget = new Widget {Count = 3, Name="Jimmy"};
    var mapper = mapperConfiguraiton.CreateMapper();

    var model = mapper.Map<WidgetModel>(widget);
}

public class Widget {
    public int Count {get; set;}
    public string Name {get;set;}
}

public class WidgetModel {
    public int Count {get; set;}
    public string Name {get;set;}
}

public static class MapperExtensions {
    public static IMappingExpression<TSource, TDestination> Increment<TSource, TDestination>(this IMappingExpression<TSource, TDestination> expression, 
        Expression<Func<TDestination, int>> destinationMember, 
        Expression<Func<TSource, int>> sourceMember) 
    {
        return expression.CustomAction(destinationMember, sourceMember, s => s + 1);
     }

    public static IMappingExpression<TSource, TDestination> ToUpper<TSource, TDestination>(this IMappingExpression<TSource, TDestination> expression, 
        Expression<Func<TDestination, string>> destinationMember, 
        Expression<Func<TSource, string>> sourceMember)
    {
        return expression.CustomAction(destinationMember, sourceMember, s => s.ToUpper());
    }


    public static IMappingExpression<TSource, TDestination> CustomAction<TSource, TDestination, TDestinationMember, TSourceMember>(
        this IMappingExpression<TSource, TDestination> expression, 
        Expression<Func<TDestination, TDestinationMember>> destinationMember, 
        Expression<Func<TSource, TSourceMember>> sourceMember, 
        Expression<Func<TSourceMember, TDestinationMember>> transform)
    {
       var sourceMemberExpression = (MemberExpression)sourceMember.Body;        
       var sourceParameter = Expression.Parameter(typeof(TSource));

       var expr = Expression.Invoke(transform, 
                                Expression
                                    .MakeMemberAccess(sourceParameter, sourceMemberExpression.Member));

        var lambda = (Expression<Func<TSource,TSourceMember>>)
            Expression.Lambda(expr, sourceParameter);

        var newExpression = expression.ForMember(
             destinationMember, 
             opts => opts.MapFrom(lambda));

        return newExpression;
    }
}

输出：

widget.Count = 3
widget.Name = "Jimmy"

model.Count = 4
model.Name = "JIMMY"

C＃更改Linq表达式的返回值

1 个答案: