如果選擇的值為null，如何使Linq選擇返回值？

Question

我有以下代碼：

    [DisplayName("Created")]
    [DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}")]
    public DateTime? Created { get; set; }

    [DisplayName("Modified By")]
    public string ModifiedBy { get; set; }

    [DisplayName("Modified")]
    [DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}")]
    public DateTime? Modified { get; set; }

        from d in data
        select new Content.Grid
        {
            PartitionKey = d.PartitionKey,
            RowKey = d.RowKey,
            Order = d.Order,
            Title = d.Title,e
            Created = d.Created,
            CreatedBy = d.CreatedBy,
            Modified = d.Modified,
            ModifiedBy = d.ModifiedBy
        };

d.Created ， d.CreatedBy ， d.Modified和d.ModifiedBy可能為空。

我怎樣才能這樣做，如果它們為null，那么select為CreatedBy和ModifiedBy返回n/a並返回Created和Modified January, 1, 2012 ？

Answer 1

您可以使用null-coalescing運算符 （ ?? ）為可空值類型或引用類型提供默認值：

from d in data
select new Content.Grid
{
    PartitionKey = d.PartitionKey,
    RowKey = d.RowKey,
    Order = d.Order,
    Title = d.Title,e
    Created = d.Created ?? new DateTime(2012,1,1),
    CreatedBy = d.CreatedBy ?? "n/a",
    Modified = d.Modified ?? new DateTime(2012,1,1),
    ModifiedBy = d.ModifiedBy ?? "n/a"
};