简短＆＃34;如果＆＃34;声明没有＆＃34;否则＆＃34;

Question

我有一个班级：

public class DriverShortInfoElement
{
    ......
    public DateTime? VistracksDateAdded { get; set; }
}

我希望用来自DbContext的数据来填充它。我想填充VistracksDateAdded只有一些条件为真，否则保留为null：

我试着这样：

var list = (from i in _db.Drivers
            select new DriverShortInfoElement()
            {
                .....
                VistracksDateAdded = (i.ProblemSyncToVistracksDriver != null) ? i.ProblemSyncToVistracksDriver.DateAdded : null
            }).ToList();

但编译错误。怎么做这个简单的事情？

Answer 1

我猜DateAdded是DateTime。如果您使用条件运算符，则必须将null强制转换为DateTime?或使用new Nullable<DateTime>()，因为null和DateTime之间不存在隐式转换：

VistracksDateAdded = i.ProblemSyncToVistracksDriver != null
    ? i.ProblemSyncToVistracksDriver.DateAdded 
    : new Nullable<DateTime>()

Answer 2

还有另一个运营商：Null conditional operator

VistracksDateAdded = i.ProblemSyncToVistracksDriver?.DateAdded

Answer 3

var query =
    from driver in _db.Drivers
    select new DriverShortInfoElement
    {
        VistracksDateAdded = driver.ProblemSyncToVistracksDriver != null
            ? driver.ProblemSyncToVistracksDriver.DateAdded
            : default(DateTime?)
    };