如果选择的值为null，如何使Linq选择返回值？

Question

我有以下代码：

    [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可能为空。

如何设置它以便如果它们为null，则select为n/a和CreatedBy返回ModifiedBy并返回{{1}的日期January, 1, 2012 }和Created？

Answer 1

您可以使用null-coalescing operator（??）为可为空的值类型或引用类型提供默认值：

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"
};