如何定义ICollection的扩展方法< T>其中T：IMyInterface在方法定义中未指定T. [英] How to Define Extension Method for ICollection<T> where T : IMyInterface without Specifying T in the Method Definition

问题描述

背景：我想在DTO被映射到实体这一点上勾住业务规则。

IEntityDto是所有可以直接映射到实体的DTO实现的接口。

单个实例正常工作：

  public static TEntity MapTo< TEntity>（this IEntityDto dto）
 {
 ...运行不需要数据库访问的业务规则... 
返回AutoMapper.Mapper.Map< TEntity>（dto）; 
} 
  

我也想以同样的方式扩展ICollection：

  public static ICollection< TEntity> MapToCollection< TEntity>（这个ICollection< IEntityDto> dtos）
 {
 ...运行不需要数据库访问的业务规则... 
返回AutoMapper.Mapper.Map< ICollection< TEntity>>（DTOS）; 
} 
  

不幸的是，MapToCollection不会显示在上下文菜单中，或者在应用于ICollection IEntityDto。

我错过了什么让它工作？我需要扩展ICollection，其中T是IEntityDto？

  public static ICollection< TEntity> MapToCollection< TDto，TEntity>（这个ICollection< TDto> dtos）其中TDto：IEntityDto 
 {
 ...做工作并返回... 
} 
  
 
 
 
以上的工作，但我希望能从集合中推断T.  
 
 
谢谢！
解决方案
您有效需要一个签名为
的方法
 
 
  public static ICollection< TEntity> MapToCollection< TEntity，TEntityDto>（
 this ICollection< TEntityDto> dtos）
其中TEntityDto：IEntityDto 
  
 ...但这会迫使你指定两个 类型的参数，我明白你不想这样做。
 
 
 
你可以做什么，而不是两个跳跃，例如
  public static class DtoExtensions 
 {
 public static CollectionMapper< TEntityDto> Map（此ICollection< TEntityDto> dtos）
其中TEntityDto：IEntityDto 
 {
返回新的CollectionMapper< TEntityDto>（dtos）; 
} 
} 
 
公共类CollectionMapper< TEntityDto>其中TEntityDto：IEntityDto 
 {
私有只读ICollection< TEntityDto> DTOS; 
 
 public CollectionMapper（ICollection< TEntityDto> dtos）
 {
 this.dtos = dtos; 
} 
 
 public ICollection< TEntity>到< TEntity>（）
 {
 //商业规则... 
返回AutoMapper.Mapper.Map< ICollection< TEntity>>（dtos）; 
 
 
  
您现在可以使用：
  var result = collection.Map（）。至< FooEntity>（）; 
  
  Map 调用推断 TEntityDto ，并在到调用中指定 TEntity 。
 
Background: I want to hook in business rules at the point that DTOs are being mapped to entities. I figured encapsulating the mapping into an extension method would be a good route.

IEntityDto is the interface that all DTOs that can be directly mapped to entities implement. 

The single instance works fine:
public static TEntity MapTo<TEntity>(this IEntityDto dto)
{
    ... Run Business Rules that don't require db access ...
    return AutoMapper.Mapper.Map<TEntity>(dto);
}
I'd like to also extend ICollection the same way:
public static ICollection<TEntity> MapToCollection<TEntity>(this ICollection<IEntityDto> dtos)
{
    ... Run Business Rules that don't require db access ...
    return AutoMapper.Mapper.Map<ICollection<TEntity>>(dtos);
}
Unfortunately, MapToCollection does not show up on the context menu or compile when applied to an ICollection of IEntityDto.

What am I missing to get this to work? Do I need to just extend ICollection where T is IEntityDto? I'd prefer to not have to include the DTO type when calling the extension method.
public static ICollection<TEntity>MapToCollection<TDto,TEntity>(this ICollection<TDto> dtos) where TDto: IEntityDto
{
    ... Do Work and Return ...
}
The above works, but I was hoping to infer T from the collection.

Thanks!
解决方案
You effectively need a method with a signature of 
public static ICollection<TEntity> MapToCollection<TEntity, TEntityDto>(
    this ICollection<TEntityDto> dtos)
    where TEntityDto : IEntityDto
... but that would force you to specify both type arguments, which I understand you don't want to do.

What you can do instead is go in two hops, e.g.
public static class DtoExtensions
{
    public static CollectionMapper<TEntityDto> Map(this ICollection<TEntityDto> dtos)
        where TEntityDto : IEntityDto
    {
        return new CollectionMapper<TEntityDto>(dtos);
    }
}

public class CollectionMapper<TEntityDto> where TEntityDto : IEntityDto
{
    private readonly ICollection<TEntityDto> dtos;

    public CollectionMapper(ICollection<TEntityDto> dtos)
    {
        this.dtos = dtos;
    }

    public ICollection<TEntity> To<TEntity>()
    {
        // Business rules...
        return AutoMapper.Mapper.Map<ICollection<TEntity>>(dtos);
    }
}
You can now use:
var result = collection.Map().To<FooEntity>();
The Map call infers TEntityDto, and you specify TEntity in the To call.

                        
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