Question

我有一些实体，这些实体可以通过自动映射器映射到域模型，并作为Iqueryable从服务中返回。如何在它们上使用.select或使用automapper projectTo来将它们映射到视图模型，因为在尝试时会抛出错误IAsyncEnumerable不能用于域模型内部导航属性上的IEnumerable类型的参数？

class HomeDomainModel
{
    public string Id { get; set; }

    public ICollection<HumanDomainModel> Humans { get; set; }
}

class HumanDomainModel
{ 
    public string Id { get; set; }
}

class HomaEntity
{
    public string Id { get; set; }

    public ICollection<HumanEntity> Humans { get; set; }
}

class HumanEntity 
{
    public string Id { get; set; }
}

// IQueryable<HomeEntity>
var homeEntities = homeEntities.GetAll();

// IQueryable<HomeDomainModel>
var homeDomainModels = humanEntity.ProjectTo<HomeDomainModel>();

// Here it throws the exception
var homeViewModel = homeDomainModels.Select(hdm => new HomeViewModel()
    {
        Id = hdm.Id,
        HumansCount = hdm.Humans.Count()
    }).ToArrayAsync();

Answer 1

如果要将ButtonColorView映射到ICollection<HumanEntity> Humans { get; set; }，可以尝试以下代码：

HumansCount
```
Profile
```

用例

public class ModelProfile: Profile
{
    public ModelProfile()
    {
        CreateMap<HomaEntity, HomeViewModel>()
            .ForMember(dest => dest.HumansCount, opt => opt.MapFrom(src => src.Humans.Count));           
    }
}

更新

对于EF Core，它在LINQ查询中具有混合客户端/数据库评估的概念。对于您的代码，var humanEntity = new List<HomaEntity> { new HomaEntity{ Id = "T1", Humans = new List<HumanEntity>(){ new HumanEntity{ Id = "H1"}, } }, new HomaEntity{ Id = "TT1", Humans = new List<HumanEntity>(){ new HumanEntity{ Id = "HH1"}, new HumanEntity{ Id = "HH2"}, } }, new HomaEntity{ Id = "TT1", Humans = new List<HumanEntity>(){ new HumanEntity{ Id = "HHH1"}, new HumanEntity{ Id = "HHH2"}, new HumanEntity{ Id = "HHH3"} } } }; // Here it throws the exception var homeViewModels = _mapper.Map<List<HomeViewModel>>(humanEntity);将在客户端运行，而HumansCount = hdm.Humans.Count()将作为服务器端或异步运行。

有两种选择适合您：

将ToArrayAsync()更改为.ToArrayAsync()
对于此限制，此问题已在EF Core 3.0中修复，如果您需要使用.ToArray()，则可以尝试使用ef core 3.0（例如，版本{）将.net core 2.2项目迁移到.net core 3.0。 {1}}

如何在域模型上使用选择

1 个答案: