在实体框架核心中将字典转换为ICollection

Posted 2021-04-11

在这里，我坚持在EF Core中将dictionary转换为Icollection。我在Dictionary类中有FlatEmployee，其中我在数据库中存储键，值对的列表。我这样宣布：

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));
}

当我播种或插入时，这非常好。但是当我试图获得FlatEmployee类时，我面临的问题。这是因为我想在Collection中获取字典。为此我已经宣布了另一个类：

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类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;
  }

这当然不会工作，因为empVM.EarningDetails.PayAndAllowances为null并抛出NullReferenceException。我的查询是如何在EmployeeEarningDTO中创建地图时在Dictionary和ICollection之间进行映射。或者请您提出宝贵的建议和解决方案。

答案

事实证明是AutoMapper映射问题。

首先，与EmployeeEarningDTO相比，LastPayCertificateViewModel内部的FlatEmployee创造了额外的水平：

LastPayCertificateViewModel.PayPayAndAllowances.PayAndAllowances

VS

FlatEmployee.PayAndAllowances

AutoMapper默认使用相同名称映射属性。因此，在FlatEmployee到LastPayCertificateViewModel地图内，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将自动尝试映射PayAndAllowances属性，但没有从KeyValuePair<string, long>到BaseEmployeeDictionary的映射。您可以定义此类映射

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));

这将允许您简单地使用

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>被映射到BaseEmployeeDictionary，所以你可以在那里进行映射：

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