在 Entity Framework Core 中将字典转换为 ICollection

Question

在这里，我遇到了在 EF Core 中将 dictionary 转换为 Icollection 的问题。我在 FlatEmployee class 中有 Dictionary，我在其中存储数据库中的键值对列表。我这样声明：

public class FlatEmployee
{
    public int EmployeeId { get; set; }
    public Dictionary<string, long> PayAndAllowances { get; set; }
}

//====================Configuration 
public void Configure(EntityTypeBuilder<FlatEmployee> builder)
{
        builder.HasKey(f => new { f.EmployeeId });
        builder.Property(sb => sb.PayAndAllowances)
            .HasConversion(
                pa => JsonConvert.SerializeObject(pa),
                pa => JsonConvert.DeserializeObject<Dictionary<string, long>>(pa));
}

这在我播种或插入时非常有效。但是我在尝试获取 FlatEmployee class 时遇到的问题。这是因为我想获取 Collection 中的字典。为此，我声明了另一个 class 这样的：

public class LastPayCertificateViewModel: IHaveCustomMapping
{
    public int EmployeeCode { get; set; }
    public EmployeeEarningDTO PayAndAllowances { get; set; }

    public void CreateMappings(Profile configuration)
    {
        configuration.CreateMap<FlatEmployee, LastPayCertificateViewModel>()
            .ForMember(dto => dto.EmployeeCode , opt => opt.MapFrom(entity => entity.EmployeeId ));
    }
}

public class EmployeeEarningDTO : IHaveCustomMapping
{
    public ICollection<BaseEmployeeDictionary> PayAndAllowances { get; set; }

    public void CreateMappings(Profile configuration)
    {
        configuration.CreateMap<FlatEmployee, EmployeeEarningDTO>()
            .ForMember(dto => dto.PayAndAllowances, opt => opt.MapFrom(entity => entity.PayAndAllowances));
    }
}

public class BaseEmployeeDictionary
{
    public string Name { get; set; }
    public long Amount { get; set; }
}

当我尝试使用上面的 classes 来获取这样的数据时：

public class LastPayCertificateQuery : IRequest<LastPayCertificateViewModel>
{
    public string EmployeeCode { get; set; }
}

public async Task<LastPayCertificateViewModel> Handle(LastPayCertificateQuery request, CancellationToken cancellationToken)
{           
    var predicate = PredicateBuilder.False<FlatEmployee>();
    predicate = predicate.Or(emp => emp.EmployeeId == request.EmployeeCode);
    var employee = await _context.FlatEmployee
                        .Where(predicate)
                        .FirstOrDefaultAsync(cancellationToken);
    if (employee == null)
        return null;
    var empVM = _mapper.Map<LastPayCertificateViewModel>(employee);
}

然后我在 PayAndAllowances in empVM 中得到 null。这就是我的问题所在。我的问题在哪里？我认为这是因为该词典具有键值对并且无法转换为 BaseEmployeeDictionary。我也尝试过这种方式将列表项添加到 PayAndAllowances in empVM

 foreach (KeyValuePair<string, long> data in employee.DeductionsByAdjustment)
 {
     BaseEmployeeDictionary listItem = new BaseEmployeeDictionary
     {
         Name = data.Key,
         Amount = data.Value
     };
     empVM.EarningDetails.PayAndAllowances.Add(listItem);
     return empVM;
  }

这当然不会起作用，因为 empVM.EarningDetails.PayAndAllowances 为 null 并抛出 NullReferenceException。我的问题是如何在 EmployeeEarningDTO 中创建映射时将字典映射到 ICollection。或者如果您提出宝贵的建议和解决方案，我们将不胜感激。

Answer 1

原来是AutoMapper映射问题

首先，LastPayCertificateViewModel 中的 EmployeeEarningDTO 与 FlatEmployee 相比创建了额外的级别：

LastPayCertificateViewModel.PayPayAndAllowances.PayAndAllowances

对

FlatEmployee.PayAndAllowances

AutoMapper 默认映射具有相同名称的属性。所以在 FlatEmployee 到 LastPayCertificateViewModel 的映射中，它会尝试将 Dictionary<string, long> PayAndAllowances 映射到 EmployeeEarningDTO PayAndAllowances。但是没有从Dictionary<string, long>到EmployeeEarningDTO的映射。相反，有一个从 FlatEmployee 到 EmployeeEarningDTO 的映射，所以你必须告诉 AM 使用它：

configuration.CreateMap<FlatEmployee, LastPayCertificateViewModel>()
    .ForMember(dto => dto.EmployeeCode, opt => opt.MapFrom(entity => entity.EmployeeId))
    .ForMember(dto => dto.PayAndAllowances, opt => opt.MapFrom(entity => entity)); // <--

其次，从FlatEmployee映射到EmployeeEarningDTO - AM会自动尝试映射PayAndAllowances属性，但是没有从KeyValuePair<string, long>映射到BaseEmployeeDictionary.你可以定义这样的映射

configuration.CreateMap<KeyValuePair<string, long>, BaseEmployeeDictionary>()
                        .ForMember(dst => dst.Name, opt => opt.MapFrom(src => src.Key))
                        .ForMember(dst => dst.Amount, opt => opt.MapFrom(src => src.Value));

这将使您可以简单地使用

configuration.CreateMap<FlatEmployee, EmployeeEarningDTO>();

但是你可能不会这样做，因为你不希望每个 KeyValuePair<string, long> 都映射到 BaseEmployeeDictionary，所以你可以这样做就地映射：

configuration.CreateMap<FlatEmployee, EmployeeEarningDTO>()
     .ForMember(dto => dto.PayAndAllowances, opt => opt.MapFrom(entity => entity.PayAndAllowances
        .Select(src => new BaseEmployeeDictionary { Name = src.Key, Amount = src.Value })));

在 Entity Framework Core 中将字典转换为 ICollection

Convert Dictionary to ICollection in Entity Framework Core

c#

ef-code-first

entity-framework-core

asp.net-core-webapi

asp.net-core-2.1