自动映射器投影和联合

本文介绍了自动映射器投影和联合的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我对联合投影和自动映射投影有问题.

I have a problem with union and automapper projections.

我有两个实体:

public class Entity { public DateTime ActionDate { get; set; } public int SomeProp { get; set; } } public class ExtendedEntity { public DateTime ActionDate { get; set; } public int SomeProp { get; set; } public int SomeOtherProp { get; set; } }

和投影:

public class EntityProjection { public DateTime ActionDate { get; set; } public int SomeProp { get; set; } public int SomeOtherProp { get; set; } public string Source { get; set; } }

我将实体映射到一个投影，因为实体没有SomeOtherProp，所以我将其设置为0:

i map entities to one projection, Entity does not have SomeOtherProp so i set 0 to it:

public class EntityProfile : Profile { protected override void Configure() { CreateMap<ExtendedEntity, EntityProjection>() .ForMember(dest => dest.Source, opt => opt.MapFrom(src => "ext entity")); CreateMap<Entity, EntityProjection>() .ForMember(dest => dest.SomeOtherProp, opt => opt.MapFrom(src => 0)) .ForMember(dest => dest.Source, opt => opt.MapFrom(src => "entity")); } }

当我尝试使用下一个代码时，出现错误:

when i try to use next code i get error:

var entities = context.Set<Entity>() .Project().To<EntityProjection>(); var extEntities = context.Set<ExtendedEntity>() .Project().To<EntityProjection>(); var result = entities.Union(extEntities).OrderBy(p => p.ActionDate).ToList();

错误文本:类型'UserQuery + EntityProjection'出现在单个LINQ to Entities查询中的两个结构不兼容的初始化中.类型可以是...

Error text: The type 'UserQuery+EntityProjection' appears in two structurally incompatible initializations within a single LINQ to Entities query. A type can be...

这意味着投影中的属性必须以相同的顺序初始化，我如何通过自动映射器设置投影属性的初始化顺序?

That means that properties in projection must be initialized in same order, how i can set projection properties initialization order by automapper?

推荐答案

答案很晚，简短的版本似乎是你不能".

Very late answer, and the short version seems to be "You can't".

我有完全相同的问题(我可以强制Automapper按一定顺序初始化属性吗?)并最终在LINQ select语句中映射所有内容.

I had exactly the same question (Can I force Automapper to initialise properties in a certain order?) and ended up mapping everything within a LINQ select statement.

为简便起见，我在DTO(缩减代码)中将其设置为静态方法:

For ease, I made it a static method within my DTO (cut-down code):

public static IQueryable<MyDto> QueryableFromTaskType1( IQueryable<TaskType1> query) { return query.Select(src => new MyDto() { TaskId = src.Id, AssetTypeName = src.Asset.AssetType.Name, AssetId = src.Asset.Id, AssetCode = src.Asset.Code, AssetName = src.Asset.Name, }); } public static IQueryable<MyDto> QueryableFromTaskType2( IQueryable<TaskType2> query) { return query.Select(src => new MyDto() { TaskId = src.Id, AssetTypeName = src.AssetTypeName, AssetId = src.AssetId, AssetCode = src.AssetCode, AssetName = src.AssetName, }); }

然后，您可以将对象作为IQueryable获取，只需将它们通过适当的静态方法(将select附加到DTO或其他已知的项目)中进行传递，然后对所得的IQueryable进行联合或合并.

then you can get your objects, as an IQueryable, simply pass them through the appropriate static method (which appends a select into the DTO - or projects as it's otherwise known) and then Union or Concat the resulting IQueryables.

唯一的缺点是Automapper通常会处理递归自动映射，尽管我可以肯定它不会很好地映射到SQL，所以您可能不会损失太多.

The only downside is that Automapper will normally deal with recursive automapping, although I'm pretty certain that wouldn't map to SQL well anyway, so you probably don't lose much.