使用Linq Select将实体映射到DTO的最简洁方法? [英] Cleanest Way To Map Entity To DTO With Linq Select?

问题描述

我一直在尝试提出一种干净且可重用的方法来将实体映射到其DTO.这是我想出的东西以及遇到问题的一个示例.

I've been trying to come up with a clean and reusable way to map entities to their DTOs. Here is an example of what I've come up with and where I'm stuck.

实体

public class Person
{
    public int ID { get; set; }
    public string Name { get; set; }
    public Address Address { get; set; }
    // Other properties not included in DTO
}

public class Address
{
    public int ID { get; set; }
    public string City { get; set; }
    // Other properties not included in DTO
}

DTO

public class PersonDTO
{
    public int ID { get; set; }
    public string Name { get; set; }
    public AddressDTO Address { get; set; }
}

public class AddressDTO
{
    public int ID { get; set; }
    public string City { get; set; }
}

表达式

这就是我开始处理映射的方式.我想要一个不会在映射之前执行查询的解决方案.有人告诉我，如果您传递Func<in, out>而不是Expression<Func<in, out>>，它将在映射之前执行查询.

This is how I began to handle the mapping. I wanted a solution that wouldn't execute the query before mapping. I've been told that if you pass a Func<in, out> instead of Expression<Func<in, out>> that it will execute the query before mapping.

public static Expressions
{
    public static Expression<Func<Person, PersonDTO>> = (person) => new PersonDTO()
    {
        ID = person.ID,
        Name = person.Name,
        Address = new AddressDTO()
        {
            ID = person.Address.ID,
            City = person.Address.City
        }
    }
}

一个问题是我已经有了一个将Address映射到AddressDTO的表达式，所以我有重复的代码.如果person.Address为null，这也会中断.这变得非常混乱，特别是如果我想在同一DTO中显示与人相关的其他实体时.它变成了嵌套映射的鸟巢.

One issue with this is that I already have an expression that maps an Address to an AddressDTO so I have duplicated code. This will also break if person.Address is null. This gets messy very quick especially if I want to display other entities related to person in this same DTO. It becomes a birds nest of nested mappings.

我尝试了以下操作，但是Linq不知道如何处理.

I've tried the following but Linq doesn't know how to handle it.

public static Expressions
{
    public static Expression<Func<Person, PersonDTO>> = (person) => new PersonDTO()
    {
        ID = person.ID,
        Name = person.Name,
        Address = Convert(person.Address)
    }

    public static AddressDTO Convert(Address source)
    {
        if (source == null) return null;
        return new AddressDTO()
        {
            ID = source.ID,
            City = source.City
        }
    }
}

我缺少任何优雅的解决方案吗?

Are there any elegant solutions that I'm missing?

推荐答案

只需使用 AutoMapper .

示例:

Mapper.CreateMap<Address, AddressDTO>();
Mapper.CreateMap<Person, PersonDTO>();

查询将在执行映射时执行，但是如果您不感兴趣的实体中有字段，请使用Project().To<>，该字段可用于NHibernate和EntityFramework.它将有效地对映射配置中指定的字段进行选择.

Your query will execute when the mapping is performed but if there are fields in the entity that you're not interested use Project().To<> which is available both for NHibernate and EntityFramework. It will effectively do a select on the fields specified in the mapping configurations.

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