Automapper

Automapper 顾名思义就是自动完成两个对象之间的copy，一个不错的教程：https://dotnettutorials.net/lesson/automapper-in-c-sharp/

不过这个教程的最后一节涉及到的UseValue 及 ResolveUsing 都已经停用了，目前有其他的方式，详见下面的例子中注释的5. 和 6. 。

 

namespace TestAutoMapper
{
    public class Address
    {
        public string City { get; set; }
        public string State { get; set; }
        public string Country { get; set; }

        public override string ToString()
        {
            return $"\n\tCity: {City}\n\tState: {State}\n\tCountry: {Country}";
        }

    }

    public class Department
    {
        public string DeptName { get; set; }

        public string DeptCity { get; set; }

        public override string ToString()
        {
            return $"\n\tDeptName: {DeptName}\n\tDeptCity: {DeptCity}";
        }
    }


    public class Employee
    {
        public string Name { get; set; }
        public int Age { get; set; }
        public int Salary { get; set; }
        public Address Address { get; set; }
        public Department Department { get; set; }
        public string SchoolName { get; set; }
        public string SchoolLoc { get; set; }
        public string Dummy { get; set; }
       

        public override string ToString()
        {
            return $"Name: {Name}\nAge: {Age}\nSalary: {Salary}\nAddress: {Address}\nDepartment: {Department}\nSchoolName: {SchoolName}\nSchoolLoc: {SchoolLoc}\nDummy: {Dummy}";
        }
    }
}

using System;

namespace TestAutoMapper
{
    public class AddressDTO
    {
        public string CityName { get; set; }
        public string State { get; set; }
        public string Country { get; set; }

        public override string ToString()
        {
            return $"\n\tCityName:{CityName}\n\tState:{State}\n\tCountry:{Country}";
        }
    }

    public class SchoolDTO
    {
        public string SchoolName { get; set; }
        public string SchoolLoc { get; set; }

        public override string ToString()
        {
            return $"\n\tSchoolName: {SchoolName}\n\tSchoolLoc: {SchoolLoc}";
        }
    }

    public class EmployeeDTO
    {
        public string FullName { get; set; }
        public int Age { get; set; }
        public int Salary { get; set; }
        public AddressDTO AddressDTO { get; set; }
        public string DeptName { get; set; }
        public string DeptCity { get; set; }
        public SchoolDTO SchoolInfo { get; set; }
        public string Dummy { get; set; }
        public string FixedItem { get; set; }
        public DateTime UpdateTime { get; set; }
        public override string ToString()
        {
            return $"FullName: {FullName}\nAge: {Age}\nSalary: {Salary}\nAddressDTO: {AddressDTO}\nDeptName: {DeptName}\nDeptCity: {DeptCity}\nSchoolInfo: {SchoolInfo}\nDummy: {Dummy}\nFixedValue: {FixedItem}\nUpdateTime: {UpdateTime}";
        }
    }
}

 

program.cs

using AutoMapper;
using System;

namespace TestAutoMapper
{

    class Program
    {
        static void Main()
        {
            var config = new MapperConfiguration(cfg =>
            {
                cfg.CreateMap<Address, AddressDTO>()
                .ForMember(dest => dest.CityName, act => act.MapFrom(src => src.City));

                cfg.CreateMap<Employee, EmployeeDTO>()
                .ForMember(dest => dest.Age, act => act.Condition(src => (src.Age > 40)))             // 1. condition mapping
                .ForMember(dest => dest.FullName, act => act.MapFrom(src => src.Name))                // 2. different name
                .ForMember(dest => dest.DeptName, act => act.MapFrom(src => src.Department.DeptName)) // 3. source itme is complex, target is primary
                .ForMember(dest => dest.DeptCity, act => act.MapFrom(src => src.Department.DeptCity))
                .ForMember(dest => dest.AddressDTO, act => act.MapFrom(src => src.Address))
                .ForMember(dest => dest.Dummy, act => act.Ignore())                                   // 4. Ignore item mapping
                .ForMember(dest => dest.FixedItem, act => act.MapFrom(src => "Fixed Value"))          // 5. set fixed value to target
                .ForMember(dest => dest.UpdateTime, act => act.MapFrom(src => DateTime.Now ))         // 6. set dynamic value to target
                .ForMember(dest => dest.SchoolInfo, act => act.MapFrom(src => new SchoolDTO()         // 7. source item is primary, target is complex
                {
                    SchoolName = src.SchoolName,
                    SchoolLoc = src.SchoolLoc
                }));
            });

            Address empAddress = new Address
            {
                City = "Mumbai",
                State = "Maharashtra",
                Country = "India"
            };

            Department empDept = new Department
            {
                DeptName = "IT",
                DeptCity = "NewYork"
            };

            Employee emp = new Employee
            {
                Name = "James",
                Age = 30,
                Salary = 20000,
                Address = empAddress,
                Department = empDept,
                SchoolName = "MIT",
                SchoolLoc = "USA",
                Dummy = "Dummy item will be ignore"
            };

            var mapper = new Mapper(config);
            var empDTO = mapper.Map<EmployeeDTO>(emp);

            var defaultColor = Console.ForegroundColor;
            Console.ForegroundColor = ConsoleColor.Red;

            Console.WriteLine("Copy from:");
            Console.WriteLine();
            Console.WriteLine(emp);
            Console.WriteLine();
            Console.ForegroundColor = ConsoleColor.Green;
            Console.WriteLine("to");
            Console.WriteLine();
            Console.WriteLine(empDTO);
            Console.ForegroundColor = defaultColor;
        }
    }
}

这个例子也很直观：将一个类Employee 的对象的值复制到另一个类 EmployeeDTO 的对象。这两个类的属性有完全一样的，也有些区别。

复制的过程中会按照如下的规则（除了0之外，其他的都对应例子中的注释）：

0. 属性相同的值会被直接复制不需要任何操作

1. 复制的时候可以加上条件，比如Age > 40才复制，否则不复制

2. 属性不一致的情况下需要额外定义，否则不会复制

3. 源数据的属性是一个复杂类型（一个类）Department，而目标是简单类型，需要明确给出对应关系

4. 如果某些属性不想复制，也可以设置为忽略 ignore

5. 给目标属性赋一个固定值

6. 给目标属性赋一个需要运算的值

7. 与 3. 相反，由简单类型复制到复杂类型

上面例子的输出如下：

 

注：本文中的例子为一个.NET console project, 使用 Nuget 安装一下 AutoMapper 即可。