可为 nullable double 和 int 之间的转换失败

Question

我有一个模型 FittingProject，我正试图将其映射到另一个模型 FittingsProjectSharepointModel。

不幸的是，FittingProject 和 FittingsProjectSharepointModel 仅共享值，属性名称和类型都不同。

为了简化映射过程，我为 FittingProject 创建了一个自定义属性，我用它来查找 FittingsProjectSharepointModel 上匹配的属性。问题是大多数值在转换过程中都会失败，例如从 int 到 double?。

正如您在下面的代码片段中看到的，我尝试使用 Convert.ChangeType，但它仍然失败并出现相同的异常。

public ModelMapper MapModelToFittingsProjectSharepointModel(object model)
{
    if (model == null)
    {
        return null;
    }

    var propertiesWithCustomAttributes = model
        .GetType()
        .GetProperties()
        .Where(p => p.GetCustomAttributes(typeof(SharepointModelPropertyAttribute), true).Length > 0);

    foreach (var prop in propertiesWithCustomAttributes)
    {
        foreach (var customAttribute in prop.GetCustomAttributes(true))
        {
            SharepointModelPropertyAttribute sharePointModelPropertyAttribute = 
                customAttribute as SharepointModelPropertyAttribute;

            PropertyDescriptor sharePointModelprop = TypeDescriptor
                .GetProperties(typeof(FittingsProjectSharepointModel))
                .Find(sharePointModelPropertyAttribute.SharepointModelProperty, false);

            try
            {
                var projectValue = prop.GetValue(model);
                var projectValueConverted = Convert.ChangeType(projectValue, sharePointModelprop.PropertyType);

                sharePointModelprop.SetValue(FittingsProjectSharepointModel, projectValueConverted);
            }
            catch (Exception ex)
            {
                // 
            }
        }
    }
    return this;
}

Answer 1

ChangeType 不支持：

Convert.ChangeType(1234, typeof(double)) //works
Convert.ChangeType(1234, typeof(double?)) //fails

因此您可能需要进行自己的可空处理。只需使用 Nullable.GetUnderlyingType 从目标类型中去除可为 null 的属性。您还需要处理这种情况，即要转换的值是 null.

Answer 2

您可以使用 AutoMapper。像这样：

考虑以下示例模型：

public class FittingProject
{
    public string Name { get; set; }
    public int Size { get; set; }
}

public class FittingsProjectSharepointModel
{
    public string Display { get; set; }
    public double? Volume { get; set; }
}

现在，您可以像这样在模型之间创建映射：

AutoMapper.Mapper.CreateMap<FittingProject, FittingsProjectSharepointModel>()
    .ForMember(dest => dest.Display, opts => opts.MapFrom(src => src.Name)) //Map Name to Display
    .ForMember(dest => dest.Volume, opts => opts.MapFrom(src => src.Size)); //Map Size to Volume

转换方法如下：

FittingProject fitting_project = new FittingProject()
{
    Name ="project_name",
    Size = 16
};

FittingsProjectSharepointModel sharepoint_model =
    AutoMapper.Mapper.Map<FittingsProjectSharepointModel>(fitting_project);

可为 nullable double 和 int 之间的转换失败

Conversion fails between nullable double and int

c#

reflection

type-conversion