c# 使用 Linq 将数组中的数组投影到新数组中？

Question

我正在使用 .NET Core 并构建 API。我有传入的 JSON，我将其映射到 C# 对象，并且在大多数情况下，JSON 非常简单，除了一个可能在数组中包含数组的部分，请参见下文:

"marketing_preferences": [
  {
    "channel": "EDM",
    "opt_in": false,
    "valid_from_date": "2020-05-30T07:07:53.723Z",
    "content_type_preferences": [
      {
        "type": "CAT",
        "opt_in": false,
        "valid_from_date": "2020-05-30T07:07:53.724Z"
      },
      {
        "type": "TAC",
        "opt_in": true,
        "valid_from_date": "2020-05-30T07:07:53.724Z"
      }
    ]
  },
  {
    "channel": "SMS",
    "opt_in": true,
    "valid_from_date": "2020-05-30T07:07:53.724Z",
    "content_type_preferences": []
  },
  {
    "channel": "SM",
    "opt_in": true,
    "valid_from_date": "2020-05-30T07:07:53.724Z",
    "content_type_preferences": []
  }
]

营销偏好可能(但可能不)包含一个或多个 content_type_preferences。因此，marketing_preferences 是一个数组，而 content_type_preferences 是该数组中的一个可选数组。在我的代码中映射或投影营销偏好非常简单:

    customer.MarketingPreferences = source.RequestCustomer.MarketingPreferences
        .Select(x => new MarketingPreferences()
        {
            ChannelId = x.Channel,
            OptIn = x.OptIn,
            ValidFromDate = x.ValidFromDate,
            UpdatedBy = Functions.DbUser,
            CreatedDate = DateTime.UtcNow,
            UpdatedDate = DateTime.UtcNow,
            UpdatingStore = null // Not passed by API
        })
        .ToList();

但是，我对将 content_type_preferences 投影到其等效对象上的语法有些困惑。以下是我试图转换到的类(class):

public partial class MarketingPreferences
{
    public MarketingPreferences()
    {
        ContentTypePreferences = new HashSet<ContentTypePreferences>();
    }

    public Guid CustomerInternalId { get; set; }
    public string ChannelId { get; set; }
    public bool? OptIn { get; set; }
    public DateTime? ValidFromDate { get; set; }
    public string UpdatedBy { get; set; }
    public DateTime? CreatedDate { get; set; }
    public DateTime? UpdatedDate { get; set; }
    public string UpdatingStore { get; set; }

    public virtual Customer CustomerInternal { get; set; }
    public virtual ICollection<ContentTypePreferences> ContentTypePreferences { get; set; }
}

和

public partial class ContentTypePreferences
{
    public Guid CustomerInternalId { get; set; }
    public string ChannelId { get; set; }
    public string TypeId { get; set; }
    public bool? OptIn { get; set; }
    public DateTime? CreatedDate { get; set; }
    public DateTime? UpdatedDate { get; set; }
    public DateTime? ValidFromDate { get; set; }
    public string UpdatedBy { get; set; }
    public string UpdatingStore { get; set; }

    public virtual MarketingPreferences C { get; set; }
    public virtual Customer CustomerInternal { get; set; }
}

我确实开始恢复到笨拙的方式来做这件事，但我真的不满意，并且更愿意尝试找到 LINQ-ish 方式来实现以下目标:

    foreach (var marketingPrefs in source.RequestCustomer.MarketingPreferences)
    {
        if (marketingPrefs.ContentTypePreferences.Length > 0)
        {
            Console.WriteLine($"marketing preference: {marketingPrefs.Channel}");
            foreach (var contentPrefs in marketingPrefs.ContentTypePreferences)
            {
                Console.WriteLine($"content preference: {contentPrefs.Type}");
                customer.ContentTypePreferences.Add(new ContentTypePreferences
                {
                    TypeId = contentPrefs.Type,
                    OptIn = contentPrefs.OptIn,
                    ValidFromDate = contentPrefs.ValidFromDate
                });
            }
        }
    }

Answer 1

简单 SelectMany 应该足以压平集合:

customer.ContentTypePreferences = source.RequestCustomer.MarketingPreferences
    .SelectMany(mp => mp.ContentTypePreferences)
    .Select(contentPrefs => new ContentTypePreferences
            {
                TypeId = contentPrefs.Type,
                OptIn = contentPrefs.OptIn,
                ValidFromDate = contentPrefs.ValidFromDate
            })
    .ToList();