需要映射成员和构造函数的自动映射器 [英] AutoMapper requiring mapping members and constructor

问题描述

我是AutoMapper的新手，我只是想找出做事情的最佳方式。

我很快就遇到了两个简单但真实的对象模型之间的映射问题。第一个用于服务层：

public sealed class GeoLocation
{
    public GeoLocation(
        double latitude,
        double longitude)
    {
        this.Latitude = latitude;
        this.Longitude = longitude;
    }

    public double Latitude { get; private set; }

    public double Longitude { get; private set; }
}

public sealed class Location
{
    public Location(
        string name,
        GeoLocation geoLocation)
    {
        this.Name = name;
        this.GeoLocation = geoLocation;
    }

    public string Name { get; private set; }

    public GeoLocation GeoLocation { get; private set; }
}

第二个是上述数据库层的简化表示：

public sealed class LocationEntity
{
    public LocationEntity(
        string name,
        double latitude,
        double longitude)
    {
        this.Name = name;
        this.Latitude = latitude;
        this.Longitude = longitude;
    }

    public string Name { get; }

    public double Latitude { get; }

    public double Longitude { get; }
}

如果我尝试使用简单的CreateMap<Location, LocationEntity>().ReverseMap()调用来映射类型，则可以预见在验证映射时会出现问题：

AutoMapperConfigurationException: 
Unmapped members were found. Review the types and members below.
Add a custom mapping expression, ignore, add a custom resolver, or modify the source/destination type
For no matching constructor, add a no-arg ctor, add optional arguments, or map all of the constructor parameters
===============================================
Location -> LocationEntity (Destination member list)
UserQuery+Location -> UserQuery+LocationEntity (Destination member list)

No available constructor.
===============================================
LocationEntity -> Location (Destination member list)
UserQuery+LocationEntity -> UserQuery+Location (Destination member list)

Unmapped properties:
GeoLocation
No available constructor.

很公平。我不想映射每个构造函数参数，所以我尝试调用ConstructUsing：

Mapper.Initialize(
    config =>
    {
        config
            .CreateMap<Location, LocationEntity>()
            .ConstructUsing((source, _) => new LocationEntity(source.Name, source.GeoLocation?.Latitude ?? 0.0, source.GeoLocation?.Longitude ?? 0));
        config
            .CreateMap<LocationEntity, Location>()
            .ConstructUsing((source, _) => new Location(source.Name, new GeoLocation(source.Latitude, source.Longitude)));
    });

但是，这仍然抱怨LocationEntity->Location映射：

AutoMapperConfigurationException: 
Unmapped members were found. Review the types and members below.
Add a custom mapping expression, ignore, add a custom resolver, or modify the source/destination type
For no matching constructor, add a no-arg ctor, add optional arguments, or map all of the constructor parameters
===============================================
LocationEntity -> Location (Destination member list)
UserQuery+LocationEntity -> UserQuery+Location (Destination member list)

Unmapped properties:
GeoLocation

不确定还能做什么，我添加了对LocationEntity->Location映射的ForMember调用：

config
    .CreateMap<LocationEntity, Location>()
    .ConstructUsing((source, _) => new Location(source.Name, new GeoLocation(source.Latitude, source.Longitude)))
    .ForMember(
        x => x.GeoLocation,
        options => options.MapFrom((source, target, _, context) => new GeoLocation(source.Latitude, source.Longitude)));

虽然这解决了问题，但在我看来，我的映射已经变得有些复杂了。我在想：有没有更好的方法来做这件事，而不牺牲我的对象模型的设计？

推荐答案

您的对象模型设计基本上只允许通过构造进行映射(转换)，因此无法充分利用AutoMapper自动和显式映射功能。

ConstructUsing用于选择用于创建目标实例的非默认构造函数，但仍需要成员映射。

您需要的是ConvertUsing方法：

跳过成员映射并使用自定义表达式转换为目标类型

Mapper.Initialize(config =>
{
    config.CreateMap<Location, LocationEntity>()
        .ConvertUsing(source => new LocationEntity(source.Name, source.GeoLocation?.Latitude ?? 0.0, source.GeoLocation?.Longitude ?? 0));
    config.CreateMap<LocationEntity, Location>()
        .ConvertUsing(source => new Location(source.Name, new GeoLocation(source.Latitude, source.Longitude)));
});

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