隐式投射数组

Question

我有两个atm相同且定义了cast的类：

 public static implicit operator SponsoredBrandViewModel(SponsoredBrand sponsoredBrand)
        =>
            new SponsoredBrandViewModel
            {
                Id = sponsoredBrand.Id,
                BrandId = sponsoredBrand.RelatedEntityId,
                To = sponsoredBrand.To,
                From = sponsoredBrand.From,
                Importance = sponsoredBrand.Importance
            };
    public static implicit operator SponsoredBrand(SponsoredBrandViewModel sponsoredBrandViewModel)
        =>
            new SponsoredBrand
            {
                Id = sponsoredBrandViewModel.Id,
                RelatedEntityId = sponsoredBrandViewModel.BrandId,
                To = sponsoredBrandViewModel.To,
                From = sponsoredBrandViewModel.From,
                Importance = sponsoredBrandViewModel.Importance
            };

我希望在它是数组时进行转换。

ar dbSponsoredBrands = await this._sponsoredBrandRepository.GetAsync();
            var viewModels = (IEnumerable<SponsoredBrandViewModel>) dbSponsoredBrands.ToEnumerable();

但这会引发无效播放异常。

有什么想法吗？

Answer 1

您正在尝试将集合对象IEnumerable<SponsoredBrand>转换为IEnumerable<SponsoredBrandViewModel>，您已在其中为实际对象定义了隐式强制转换运算符。您需要遍历集合并创建一个新集合，例如

var dbSponsoredBrands = await this._sponsoredBrandRepository.GetAsync();
var viewModels = dbSponsoredBrands.Select(x => (SponsoredBrandViewModel)x);

Answer 2

您可以使用 LINQ -Functions

.Cast<SponsoredBrandViewModel>()

或

.OfType<SponsoredBrandViewModel>()

实现这一目标。这些也将以一种懒惰的方式迭代结果。如果您确定每个元素都属于这种类型，请使用第一个元素，如果您只想过滤匹配元素，则使用后者。