Question

我正在尝试使用AutoMapper的ProjectTo扩展方法将基于Entity Framework表的对象转换为自定义DTO。 EF侧的Person实体如下所示：

public partial class Person
{
    public int PersonId { get; set; }
    public string Name { get; set; }
    public string Age { get; set; }
}

我投射的PersonViewModel DTO看起来像这样：

public class PersonViewModel
{
    public PersonViewModel(Person p)
    {
        PersonId = p.PersonId;
        Name = p.Name;
        Age = Convert.ToInt32(p.Age);
    }

    public PersonViewModel()
    {

    }

    public PersonViewModel(int id, string name, int age)
    {
        PersonId = id;
        Name = name;
        Age = age;
    }

    public int PersonId { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

需要注意的关键是person表包含一个名为Age的字段，它是一个nvarchar类型，PersonViewModel包含一个Age类型的int类型。不幸的是，我无法更改表格，必须找到转换数据的方法。

以下代码是我尝试过的AutoMapper配置，它们的问题＆＃34;以及消耗代码（数据库调用等）。

MapperConfiguration config = new MapperConfiguration(cfg => 
        {
            // -----  Throws "Unable to create map expression" exception  ------
            //cfg.CreateMap<Person, PersonViewModel>();


            // -----  Throws "Linq to Entities does not support method" exception  ------
            //cfg.CreateMap<Person, PersonViewModel>()
            //    .ForMember(dest => dest.Age, opt => opt.MapFrom(src => Convert.ToInt32(src.Age)));


            // -----  Throws "Unable to create map expression" exception  ------
            //cfg.CreateMap<Person, PersonViewModel>()
            //    .ConstructProjectionUsing(src => new PersonViewModel
            //    {
            //        PersonId = src.PersonId,
            //        Name = src.Name,
            //        Age = Convert.ToInt32(src.Age)
            //    });


            // -----  Throws "Unable to create map expression" exception  ------
            //cfg.CreateMap<Person, PersonViewModel>()
            //    .ConstructProjectionUsing(src => new PersonViewModel(src.PersonId, src.Name, Convert.ToInt32(src.Age)));


            // -----  Throws "Unable to create map expression" exception  ------
            //cfg.CreateMap<Person, PersonViewModel>()
            //    .ConstructProjectionUsing(src => new PersonViewModel(src.PersonId, src.Name, 25));


            // -----  Throws "Linq to Entities does not support method" exception  ------
            //cfg.CreateMap<Person, PersonViewModel>()
            //    .ProjectUsing(src => new PersonViewModel
            //    {
            //        PersonId = src.PersonId,
            //        Name = src.Name,
            //        Age = Convert.ToInt32(src.Age)
            //    });


            // -----  Throws "Unable to create map expression" exception  ------
            //cfg.CreateMap<Person, PersonViewModel>()
            //    .ConstructUsing(src => new PersonViewModel
            //    {
            //        PersonId = src.PersonId,
            //        Name = src.Name,
            //        Age = Convert.ToInt32(src.Age)
            //    });


            // -----  Throws "Unable to create map expression" exception  ------
            //cfg.CreateMap<Person, PersonViewModel>()
            //    .ConstructUsing(src => new PersonViewModel(src));


            // -----  Doesn't throw exception, but all values are null or 0.  ------
            //cfg.CreateMap<Person, PersonViewModel>()
            //    .ConvertUsing(src => new PersonViewModel
            //    {
            //        PersonId = src.PersonId,
            //        Name = src.Name,
            //        Age = Convert.ToInt32(src.Age)
            //    });


            // -----  Doesn't throw exception, but all values are null or 0.  ------
            //cfg.CreateMap<Person, PersonViewModel>()
            //    .ConvertUsing(src => new PersonViewModel(src.PersonId, src.Name, Convert.ToInt32(src.Age)));


            // -----  Works, but bypasses the conversion I need  ------
            //cfg.CreateMap<Person, PersonViewModel>()
            //    .ProjectUsing(src => new PersonViewModel
            //    {
            //        PersonId = src.PersonId,
            //        Name = src.Name,
            //        Age = 25
            //    });


            // -----  Works, but bypasses the conversion I need  ------
            cfg.CreateMap<Person, PersonViewModel>()
                .ForMember(dest => dest.Age, opt => opt.MapFrom(src => 35));
        });

        using (FamilyEntities db = new FamilyEntities())
        {
            PersonViewModel p = db.Set<Person>()
                .Where(x => x.PersonId == 1)
                .ProjectTo<PersonViewModel>(config)
                .SingleOrDefault();

            Console.WriteLine("Name: " + p.Name + Environment.NewLine + "Age: " + p.Age);
        }

        Console.ReadLine();

使用AutoMapper的ProjectTo可以将字符串转换为int吗？其次，如果可能，那个配置是什么样的？

提前感谢您的帮助。

Answer 1

你的第一次尝试是为什么这不起作用。实体框架不知道如何将字符串转换为int，因此您需要进行软管理。其他方面都不重要，重要的是EF给你的例外。

如果EF无法支持转换，那么AutoMapper无法帮助您。

相反，我会在您的视图模型中执行类似转换的操作：

public class PersonViewModel
{
    public int PersonId { get; set; }
    public string Name { get; set; }
    public string Age { get; set; }
    public int AgeValue => Convert.ToInt32(Age);
}

Answer 2

https://stackoverflow.com/a/24027242/1736944说明了如何向EF添加功能。基本上生成的查询必须执行类型转换。

具有字段级别类型转换的AutoMapper.ProjectTo

2 个答案: