【AutoMapper基础】值解析器--Custom value resolvers

【简介】：

虽然AutoMapper已经覆盖了大部分的映射场景，但是还有1%~5%的情况需要值解析器的帮助。

很多时候，值解析器实现的功能可以直接在实体层通过逻辑代码直接实现，然而，如果这种逻辑只是映射时需要,这就会混乱我们的源类型以及带来不必要的操作。

这种情况下，AutoMapper允许成员配置自定义值解析器以达到想要的效果。

【示例】

接上例：【AutoMapper基础】简单示例--Flatenning

如果computer中有多个InternalMemory，那么在ComputerMainInfo中要取得InternalMemorySize时就需要将所有的InternalMemory的Size相加。

【类图】

【Code】

Computer:

public class Computer
    {
        public string Name { get; set; }
        public double Price { get; set; }
        public DateTime ProduceDate { get; set; }
        public CPU CPU { get; set; }
        public List<InternalMemory> InternalMemories { get; set; }
        public Monitor Monitor { get; set; }
    }

值解析器CustomResolver：

public class CustomResolver : ValueResolver<Computer, double>
    {
        protected override double ResolveCore(Computer source)
        {
            double totalSize = 0.0;
            foreach (var item in source.InternalMemories)
            {
                totalSize += item.Size;
            }
            return totalSize;
        }
    }

Program:

class Program
    {
        static void Main(string[] args)
        {
            Computer computer = new Computer()
            {
                Name = "联想Y450",
                Price = 5199.00,
                ProduceDate = new DateTime(2009, 10, 10),
                CPU = new CPU()
                {
                    MainFrequency = 2.2,
                    ModelName = "Core T6600",
                    ProducerName = "Intel"
                },
                InternalMemories = new List<InternalMemory>(){
                    new InternalMemory()
                    {
                        Frequency = 1333,
                        ModelName = "DDR3",
                        ProducerName = "尔必达",
                        Size = 4.0
                    },
                    new InternalMemory()
                    {
                        Frequency = 1333,
                        ModelName = "DDR3",
                        ProducerName = "尔必达",
                        Size = 4.0
                    }
                },
                Monitor = new Monitor()
                {
                    ProducerName = "LG",
                    Size = 14.0
                }
            };

            // 添加值解析器映射
            AutoMapper.Mapper.CreateMap<Computer, ComputerMainInfo>().ForMember(dest => dest.InternalMemorySize,
                            opt => opt.ResolveUsing<CustomResolver>()
                        );

            ComputerMainInfo computerMainInfo = AutoMapper.Mapper.Map<Computer, ComputerMainInfo>(computer);

            Console.WriteLine(computerMainInfo.CPUModelName);
            Console.WriteLine(computerMainInfo.InternalMemorySize);
            Console.Read();
        }
    }

这样通过值解析器就能计算出内存的总大小了。