使用AutoMapper时Expression的转换

此文章为转载：http://www.bubuko.com/infodetail-699735.html

参考链接：

http://q.cnblogs.com/q/34480/   dudu有回复，其中一个链接http://stackoverflow.com/questions/7424501/automapper-for-funcs-between-selector-types可以打开，并且本人主要参考此链接进行修改

下文链接为automapper相关源码

http://www.symbolsource.org/Public/Metadata/NuGet/Project/AutoMapper/3.3.0-ci1017/Release/Unsupported,Version%3Dv0.0/AutoMapper/AutoMapper/Internal/MappingExpression.cs?ImageName=AutoMapper

 

以下为转载内容：

 

问题描述

项目中使用AutoMapper进行VO&DTO&Entity的互相映射，但是默认Map方法不支持Expression的转换。如

Expression<Func<Entity,bool>> fun = _ => _.A == "A";

希望转换成

Expression<Func<Dto,bool>> fun = _ => _.A == "A";

 

似乎解决方案就是解析ExpressionTree并映射替换节点。正好找到了人家的提问和解决方案

http://stackoverflow.com/questions/7424501/automapper-for-funcs-between-selector-types

 

改造一下支持泛型，代码如下：

#region using namespace

using System;
using System.Collections.Concurrent;
using System.Linq.Expressions;
using System.Reflection;
using AutoMapper;
using AutoMapper.QueryableExtensions;

#endregion

namespace Core
{
    public static class FunctionCompositionExtensions
    {
        private static readonly ConcurrentDictionary<Tuple<Type, Type>, Tuple<MethodInfo, Expression>> Dictionary =
            new ConcurrentDictionary<Tuple<Type, Type>, Tuple<MethodInfo, Expression>>();

        private static readonly MethodInfo Method = typeof (FunctionCompositionExtensions).GetMethod("Compose",
            BindingFlags.NonPublic | BindingFlags.Static);

        public static Expression<Func<TDestination, bool>> MapExpression<TSource, TDestination>(
            this Expression<Func<TSource, bool>> selector)
        {
            var bulidMethod = Dictionary.GetOrAdd(new Tuple<Type, Type>(typeof (TSource), typeof (TDestination)), _ =>
            {
                var expression = Mapper.Engine.CreateMapExpression<TDestination, TSource>();
                return new Tuple<MethodInfo, Expression>(
                    Method.MakeGenericMethod(typeof (TDestination), typeof (bool), typeof (TSource)), expression);
            });
            return
                bulidMethod.Item1.Invoke(null, new object[] {selector, bulidMethod.Item2}) as
                    Expression<Func<TDestination, bool>>;
        }

        public static Expression<Func<TX, TY>> Compose<TX, TY, TZ>(this Expression<Func<TZ, TY>> outer,
            Expression<Func<TX, TZ>> inner)
        {
            return Expression.Lambda<Func<TX, TY>>(
                ParameterReplacer.Replace(outer.Body, outer.Parameters[0], inner.Body),
                inner.Parameters[0]);
        }

        public static Expression<Predicate<TX>> ComposePredicate<TX, TZ>(this Expression<Predicate<TZ>> outer,
            Expression<Func<TX, TZ>> inner)
        {
            return Expression.Lambda<Predicate<TX>>(
                ParameterReplacer.Replace(outer.Body, outer.Parameters[0], inner.Body),
                inner.Parameters[0]);
        }
    }

    class ParameterReplacer : ExpressionVisitor
    {
        private readonly ParameterExpression _parameter;
        private readonly Expression _replacement;

        private ParameterReplacer(ParameterExpression parameter, Expression replacement)
        {
            _parameter = parameter;
            _replacement = replacement;
        }

        public static Expression Replace(Expression expression, ParameterExpression parameter, Expression replacement)
        {
            return new ParameterReplacer(parameter, replacement).Visit(expression);
        }

        protected override Expression VisitParameter(ParameterExpression parameter)
        {
            if (parameter == _parameter)
            {
                return _replacement;
            }
            return base.VisitParameter(parameter);
        }
    }
}

 

测试

public class Entity
{
public string A { get; set; }
}

public class Dto
{
public string A { get; set; }
}


Mapper.CreateMap<Entity, Dto>();
Mapper.CreateMap<Dto, Entity>();


var list = new List<Dto>()
{
new Dto() {A = "A"},
new Dto() {A = "B"},
new Dto() {A = "C"},
new Dto() {A = "D"},
new Dto() {A = "E"},
};

//Predicate<Entity> fun = _ => _.A =="A";
Expression<Func<Entity,bool>> funEntity = _ => _.A == "A";

var query = list.Where(funEntity.MapExpression<Entity, Dto>().Compile());
Assert.True(query.Count() == 1);

Expression<Func<Entity, bool>> funEntity2 = _ => _.A == "F";
var query2 = list.Where(funEntity2.MapExpression<Entity, Dto>().Compile());
Assert.True(query2.Count() == 0);