抽象 Automapper 投影

Question

我使用 Entity Framework 6 开发 web api 应用程序。 我想集成并开始使用 Automapper 来映射到我的 EF 实体模型。

我已经阅读了有关投影的内容，并意识到如果我决定使用 Automapper，则有必要使用 Project().To 以获得更好的性能。但是，我不想将我的 DAL 暴露给 Automapper 库。

有没有办法可以抽象出 Automapper Project()？

提前致谢

Answer 1

1. 使用“投影”方法创建界面，可以复制 原始 AutoMapper 方法。
2. 然后创建一个具体的实现。
3. 然后将此接口添加到存储库的构造函数中。
4. 使用它
5. 将接口注册到您的依赖注入容器。
6. 按 F5

这是一个完整的例子
（当然，您将在正确的层中拥有每个类/接口）。

using AutoMapper;
using AutoMapper.QueryableExtensions;
using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Linq.Expressions;

namespace ConsoleApplicationMapper
{
    class Program
    {
        static void Main(string[] args)
        {
            Mapper.Initialize(c =>
            {
                c.CreateMap<Customer, CustomerModel>();
            });

            //If you use a dependency injection container you don't have to use the constructors
            var repository = new CustomerRepository(new EntityProjector());

            foreach (var item in repository.GetCustomers())
            {
                Console.WriteLine(item.Name);
            }

            Console.ReadLine();
        }
    }

    public class CustomerModel
    {
        public int CustomerId { get; set; }
        public string Name { get; set; }
    }

    public interface IEntityProjector
    {
        IQueryable<TDestination> ProjectTo<TDestination>(IQueryable source, params Expression<Func<TDestination, object>>[] membersToExpand);
    }

    public class EntityProjector : IEntityProjector
    {
        public IQueryable<TDestination> ProjectTo<TDestination>(IQueryable source, params Expression<Func<TDestination, object>>[] membersToExpand)
        {
            return source.ProjectTo(membersToExpand);
        }
    }

    public interface ICustomerRepository
    {
        IEnumerable<CustomerModel> GetCustomers();
    }

    public class CustomerRepository : ICustomerRepository
    {
        private readonly IEntityProjector projector;
        public CustomerRepository(IEntityProjector theProjector)
        {
            projector = theProjector;
        }
        public IEnumerable<CustomerModel> GetCustomers()
        {
            MyContext context = new MyContext();

            //Uncomment this if you want to confirm that only CustomerId,Name are selected and not LastName
            //context.Database.Log = s => Console.WriteLine(s);

            return context.Customers.SelectTo<CustomerModel>();
        }
    }

    public class Customer
    {
        public int CustomerId { get; set; }
        public string Name { get; set; }
        public string LastName { get; set; }
    }


    public class MyContext : DbContext
    {
        public DbSet<Customer> Customers { get; set; }
    }

    public static class MyExtentions
    {
        static IEntityProjector projector;
        static MyExtentions()
        {
            //You can get it from your dependecy injection container if you use one
            projector = new EntityProjector();
        }
        //I renamed this SelectTo instead of ProjectTo so you don't have any conflict if you use AutoMapper
        //Change it to to ProjectTo if you want
        public static IQueryable<TDestination> SelectTo<TDestination>(this IQueryable source, params Expression<Func<TDestination, object>>[] membersToExpand)
        {
            return projector.ProjectTo<TDestination>(source);
        }
    }
}