c#使用Linq将数组中的数组投影到新数组上？

我正在使用.NETCore并构建一个API。我有一个传入的JSON，我正在将其映射到C#对象，在大多数情况下，JSON非常简单，除了一个部分可能在数组中有一个数组，请参见下面：

"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": []
  }
]

营销首选项可能（但可能不）包含一个或多个内容类型首选项。因此，marketing_preferences是一个数组，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();

然而，我有点拘泥于将content\u type\u首选项投影到其等效对象的语法。以下是我尝试投影到的类：

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; }
}

我确实开始恢复到一种笨拙的方式，但我真的不满意，我更愿意尝试找到一种灵巧的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
                });
            }
        }
    }

简单应该足以使集合扁平化：

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

---

我确实找到了一种方法来解决这个问题，使用下面的方法

    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,
            ContentTypePreferences = (from c in x.ContentTypePreferences
                    select new ContentTypePreferences
                    {
                        TypeId = c.Type,
                        OptIn = c.OptIn,
                        ValidFromDate = c.ValidFromDate,
                        ChannelId = x.Channel // Should inherit parent marketing preference channel
                    }).ToList(),
            UpdatingStore = null // Not passed by API
        })
        .ToList();

---

我很欣赏其他答案，但我意识到仅仅平展可能还不够，因为每个ContentTypePreference的ChannelId并没有随POST JSON一起传递，而是源自该ContentTypePreference的父MarketingTypePreference（例如，电子邮件的子级将具有电子邮件的频道Id）因此，在为Entity Framework创建每个新的ContentTypePreferences时，上面的解决方案允许我注入这一点。

SelectMany有效吗？嗨，mjwills，你能用一个例子来说明你的意思吗？这是否回答了你的问题？

    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,
            ContentTypePreferences = (from c in x.ContentTypePreferences
                    select new ContentTypePreferences
                    {
                        TypeId = c.Type,
                        OptIn = c.OptIn,
                        ValidFromDate = c.ValidFromDate,
                        ChannelId = x.Channel // Should inherit parent marketing preference channel
                    }).ToList(),
            UpdatingStore = null // Not passed by API
        })
        .ToList();