EmitMapper自动映射工具

         在实体与DTO之间，咱们通常都须要进行映射。若是手动的来进行转换，实在是太麻烦。因此就产生了不少映射工具，好比AutoMapper,EmitMapper。而通过一些对比，EmitMapper比较快，接近于手工转换的速度。

          EmitMapper使用很是简单，对于那种属性名同样的，直接使用默认映射便可。如：

ObjectsMapper<From,To> mapper = ObjectMapperManager.DefaultInstance.GetMapper<From,To>();

to = mapper.Map(from);

        它就会自动的把From对象的值赋给To对象;

       对于有必定规则的,可使用一些扩展的方法,如:

      经过使用ConvertUsing能够配置一些组合映射.好比这个字段能够是某两个字段拼接,或者其余一些计算.具体能够参见一些使用例子:

       http://www.cnblogs.com/aaa6818162/archive/2012/06/21/2557879.html

      http://www.cnblogs.com/wuhong/archive/2011/09/21/2184313.html

          可是在使用的过程当中,发现了一个问题,就是自己默认是若是属性名相同就直接映射,而使用ConvertUsing是能够自定义映射条件的.可是若是使用了ConvertUsing,那么你必需为里面每一个字段都指定映射的条件.而其实真正想用的是,在实体与DTO之间,其实大部分字段的属性名称是相同的,对于这些字段,咱们是想直接默认映射,而对于其余一些须要自定义映射的字段,来自定义映射规则.但实际上却达不到这种效果,通常人也不想去把每一个字段的映射规则配置一下,若是这样,还不如手动写呢.

          后来在网上找到了一个例子,可使用FlatteringConfig这个自定义配置,这个类在EmitMapper的源码中是有的,可是不是在当前的解决方案下,而是在一个叫EMConfigurations的项目里.能够这样使用这个自定义配置.

public class User

{

  public Guid Id { get; set; }

  public Company Company { get; set; }

}    

public class Company

{

  public Guid Id { get; set; }

}

public class UserDTO

{

  public Guid Id { get; set; }

  public Guid CompanyId{ get; set; }

}

ObjectMapperManager.DefaultInstance.GetMapper<User, UserDTO>(

                new FlatteringConfig()

            );

var dto = mapper.Map(new User());

          这样,它就会自动的给DTO中的CompanyId赋值,也会给Id赋值.不过有一个规则就是CompanyId的命名要有必定的规则,必定要是那个实体的名称再加上这个实体里面属性的名称.这样才能进行自动的映射.(不过这时,若是那个实体为null,那也有可能会报错,没有试过,后面有时间试一下).

          在运行的过程当中,发现了FlatteringConfig类的一个bug;这个类的原始代码以下:

public class FlatteringConfig : DefaultMapConfig 

    {

        protected Func<string, string, bool> nestedMembersMatcher;

        public FlatteringConfig()

        {

            nestedMembersMatcher = (m1, m2) => m1.StartsWith(m2);

        }

        public override IMappingOperation[] GetMappingOperations(Type from, Type to)

        {

            var destinationMembers = GetDestinationMemebers(to);

            var sourceMembers = GetSourceMemebers(from);

            var result = new List<IMappingOperation>();

            foreach (var dest in destinationMembers)

            {

                var matchedChain = GetMatchedChain(dest.Name, sourceMembers).ToArray();

                if (matchedChain == null || matchedChain.Length == 0)

                {

                    continue;

                }

                result.Add(

                    new ReadWriteSimple

                    {

                        Source = new MemberDescriptor(matchedChain),

                        Destination = new MemberDescriptor(new[] { dest })

                    }

                );

            }

            return result.ToArray();

        }

        public DefaultMapConfig MatchNestedMembers(Func<string, string, bool> nestedMembersMatcher)

        {

            this.nestedMembersMatcher = nestedMembersMatcher;

            return this;

        }

        private List<MemberInfo> GetMatchedChain(string destName, List<MemberInfo> sourceMembers)

        {

            var matches = sourceMembers.Where(s => MatchMembers(destName, s.Name) || nestedMembersMatcher(destName, s.Name));

            int len = 0;

            MemberInfo match = null;

            foreach (var m in matches)

            {

                if (m.Name.Length > len)

                {

                    len = m.Name.Length;

                    match = m;

                }

            }

            if (match == null)

            {

                return null;

            }

            var result = new List<MemberInfo> { match };

            if (!MatchMembers(destName, match.Name))

            {

                result.AddRange(

                    GetMatchedChain(destName.Substring(match.Name.Length), GetDestinationMemebers(match))

                );

            }

            return result;

        }

        private static List<MemberInfo> GetSourceMemebers(Type t)

        {

            return GetMemebers(t)

                .Where(

                    m => 

                        m.MemberType == MemberTypes.Field || 

                        m.MemberType == MemberTypes.Property ||

                        m.MemberType == MemberTypes.Method

                )

                .ToList();

        }

        private static List<MemberInfo> GetDestinationMemebers(MemberInfo mi)

        {

            Type t;

            if (mi.MemberType == MemberTypes.Field)

            {

                t = mi.DeclaringType.GetField(mi.Name).FieldType;

            }

            else

            {

                t = mi.DeclaringType.GetProperty(mi.Name).PropertyType;

            }

            return GetDestinationMemebers(t);

        }

        private static List<MemberInfo> GetDestinationMemebers(Type t)

        {

            return GetMemebers(t).Where(m => m.MemberType == MemberTypes.Field || m.MemberType == MemberTypes.Property).ToList();

        }

        private static List<MemberInfo> GetMemebers(Type t)

        {

            BindingFlags bindingFlags = BindingFlags.Instance | BindingFlags.Public;

            return t.GetMembers(bindingFlags).ToList();

        }

    }

      在GetMappingOperations方法中,修改了如下代码:(原代码中是一个判断在一块儿,改为分做两个判断)

var matchedChainSingle = GetMatchedChain(dest.Name, sourceMembers);

               if (matchedChainSingle == null)

               {

                   continue;

               }

               var matchedChain = matchedChainSingle.ToArray();

               if (matchedChain.Length == 0)

               {

                   continue;

               }

 

      参考资料:

      http://emitmapper.codeplex.com/

      http://stackoverflow.com/questions/9619265/emit-mapper-flattering-and-property-name-mismatch

      http://emitmapper.codeplex.com/SourceControl/changeset/view/69894#1192663

      http://emitmapper.codeplex.com/SourceControl/changeset/view/42128#691132

     http://stackoverflow.com/questions/12542749/emitmapper-flattering-config-nullreferenceexception?rq=1