一、什麼是AutoMapper?

AutoMapper是一個簡單的對象映射框架(OOM)，將一個對象映射到另一個對象。

二、AutoMapper的好處

以前的時候我們將DTO對象轉換為Model對象時,我們必須將每一個屬性都手動映射

實體類

    /// <summary>
    /// 用戶表
    /// </summary>
    [Table("tb_User")]
    public class TbUser
    {
        /// <summary>
        /// 用戶Id
        /// </summary>
        [Key]
        [Column("userId")]
        [StringLength(32)]
        public string UserId { get; set; }
        /// <summary>
        /// 用戶名
        /// </summary>
        [Column("userName")]
        [StringLength(20)]
        public string UserName { get; set; }
        /// <summary>
        /// 郵箱
        /// </summary>
        [Column("email")]
        [StringLength(30)]
        public string Email { get; set; }
        /// <summary>
        /// 添加時間
        /// </summary>
        [Column("addTime")]
        [Required]
        public DateTime AddTime { set; get; }
    }

DTO傳輸對象

    /// <summary>
    /// 用戶傳輸對象
    /// </summary>
    public class UserDto
    { 
        /// <summary>
        /// 用戶Id
        /// </summary>
        [StringLength(32, ErrorMessage = "{0}最多{1}個字元"), Display(Name = "用戶Id")]
        public string UserId { get; set; }
        /// <summary>
        /// 用戶名
        /// </summary>
        [StringLength(20, ErrorMessage = "{0}最多{1}個字元"), Display(Name = "用戶名")]
        public string UserName { get; set; }
        /// <summary>
        /// 郵箱
        /// </summary>
        [StringLength(30, ErrorMessage = "{0}最多{1}個字元"), Display(Name = "郵箱")]
        public string Email { get; set; }
    }

業務層

    /// <summary>
    /// 業務處理
    /// </summary>
    public class UserService : IUserService
    {
        private readonly MyDbContext _dbContext;

        /// <summary>
        /// 構造函數
        /// </summary>
        /// <param name="dbContext"></param>
        public UserService(MyDbContext dbContext)
        {
            _dbContext = dbContext;
        }
        /// <summary>
        /// 添加用戶
        /// </summary>
        /// <param name="dto">實體傳輸對象</param>
        /// <returns></returns>
        public int Add(UserDto dto)
        {
            var user = new TbUser
            {
                UserId = Guid.NewGuid().ToString("N"),
                Email = dto.Email,
                UserName = dto.UserName,
                AddTime = DateTime.Now
            };
            _dbContext.Add(user);
            return _dbContext.SaveChanges();
        }
        /// <summary>
        /// 編輯用戶信息
        /// </summary>
        /// <param name="dto">實體傳輸對象</param>
        /// <returns></returns>
        public int Update(UserDto dto)
        {
            var user = _dbContext.TbUsers.Find(dto.UserId);
            if(user==null) throw new Exception("獲取用戶信息失敗");
            user.UserName = dto.UserName;
            user.Email = dto.Email;
            return _dbContext.SaveChanges();
        }
    }

這樣情況還可以，屬性不是很多，如果屬性過多（幾十，幾百），還需要手動賦值，簡直太頭疼了，還會導致大量的時間浪費在對象轉換中，用AutoMapper，只需要簡單的配置就可以完成兩個對象之間的屬性映射，開發中省去了屬性轉換的時間，從而提高工作效率。

三、使用AutoMapper

安裝引用

通過程式包管理器控制台安裝AutoMapper

Install-Package AutoMapper -version 9.0.0

Install-Package AutoMapper.Extensions.Microsoft.DependencyInjection -version 7.0.0

配置映射關係

創建一個類並繼承autoMapper的Profile類

    public class Mappings : Profile
    {
        public Mappings()
        {
            CreateMap<UserDto, TbUser>();
        }
    }

註入服務

            //註入AutoMapper服務，Mappings就是自己創建的映射類
            services.AddAutoMapper(typeof(Mappings));

 修改業務層代碼

    /// <summary>
    /// 業務處理
    /// </summary>
    public class UserService : IUserService
    {
        private readonly MyDbContext _dbContext;
        /// <summary>
        /// 註入介面
        /// </summary>
        private readonly IMapper _mapper;

        /// <summary>
        /// 構造函數
        /// </summary>
        /// <param name="dbContext"></param>
        /// <param name="mapper"></param>
        public UserService(MyDbContext dbContext,IMapper mapper)
        {
            _dbContext = dbContext;
            _mapper = mapper;
        }
        /// <summary>
        /// 添加用戶
        /// </summary>
        /// <param name="dto">實體傳輸對象</param>
        /// <returns></returns>
        public int Add(UserDto dto)
        {
            var info = _mapper.Map<UserDto, TbUser>(dto);
            info.AddTime=DateTime.Now;
            info.UserId = Guid.NewGuid().ToString("N");
            //var user = new TbUser
            //{
            //    UserId = Guid.NewGuid().ToString("N"),
            //    Email = dto.Email,
            //    UserName = dto.UserName,
            //    AddTime = DateTime.Now
            //};
            _dbContext.Add(info);
            return _dbContext.SaveChanges();
        }
        /// <summary>
        /// 編輯用戶信息
        /// </summary>
        /// <param name="dto">實體傳輸對象</param>
        /// <returns></returns>
        public int Update(UserDto dto)
        {
            var user = _dbContext.TbUsers.Find(dto.UserId);
            if(user==null) throw new Exception("獲取用戶信息失敗");
            //user.UserName = dto.UserName;
            //user.Email = dto.Email;
            _mapper.Map(dto, user);
            return _dbContext.SaveChanges();
        }
    }

運行測試

PS：一般在使用AutoMapper轉換時dto中欄位名稱要跟實體對象定義一樣才能轉換成功。